DIAGNOSIS
SYSTEM DIAGNOSIS
diagnostic system check
test description
The numbers below refer to the step numbers on the diagnostic table.
- This step insures that the battery, and the vehicle primary power and ground systems are functioning correctly.
- Lack of communication may be due to a particular malfunction of a serial data circuit.
- This step insures that all data link communication DTCs are diagnosed before system level DTCs.
- This step insures that all electronic control unit (ECU) internal DTCs are diagnosed before other system level DTCs.
- This step insures that all device voltage DTCs are diagnosed before other system level DTCs.
diagnostic system check
| step | action | value(s) | yes | no |
| 1 | perform the following preliminary inspections: - ensure that the battery is fully charged.
- ensure that the battery cables are clean and tight.
- inspect for any open fuses.
- inspect the easily accessible systems or the visible system components for obvious damage or conditions that could cause the symptom.
- ensure that the grounds are clean, tight, and in the correct location.
- inspect for aftermarket devices that could affect the operation of the system.
- search for applicable service bulletins.
did you find and correct the condition? | - | system ok | go to step 2 |
| 2 | install a scan tool. does the scan tool power up? | - | go to step 3 | go to scan tool does not power up |
| 3 | attempt to start the engine. does the engine crank? | - | go to step 4 | |
| 4 | attempt to start the engine. does the engine start and idle? | - | go to step 5 | |
| 5 | Important : Do not clear any DTCs unless instructed by a diagnostic procedure. use the appropriate scan tool selections to obtain dtcs for each of the control modules. does the scan tool display any dtcs? | - | go to step 6 | |
| 6 | does the scan tool display any dtcs that begin with a "U"? | - | go to applicable dtc table | - |
| 7 | Important : If any of these DTCs are displayed, diagnose them before diagnosing any other DTCs or symptoms. does the scan tool display dtcs related to control module internal fault? | - | go to applicable dtc table | go to step 8 |
| 8 | Important : If any of these DTCs are displayed, diagnose them before diagnosing any other DTCs or symptoms. does the scan tool display dtcs related to the fault in the battery/ignition voltage supply to control module? | - | go to applicable dtc table | go to step 9 |
| 9 | if multiple dtcs are stored, diagnose the dtcs in the following order: - component level dtcs, such as sensor dtcs, solenoid dtcs, and relay dtcs.
- system level dtcs, such as misfire dtcs, evaporative emission (evap) system dtcs, and fuel trim dtcs.
- diagnose the remaining dtcs.
is the customer concerned with the other symptoms? | - | | system ok |
symptoms – engine controls
important preliminary inspections before starting
Before using this section, perform the Diagnostic System Check in this section and verify all of the following conditions :
- the engine control module (ecm) and the malfunction indicator lamp (mil) are operating correctly.
- diagnostic trouble codes (dtcs) are not stored.
- the scan tool data is within the normal operating range.
- verify the customer concern and locate the correct symptom. Inspect the items indicated under that symptom.
- several of the symptom procedures ask for a careful visual/physical inspection. This step is extremely important, and can lead to correcting a condition without further inspections and can save valuable time.
- verify the proper installation of any of the following non-original equipment accessories:
- Lights
- Cellular phone
- Remote starter system
- Non-factory installed alarm
visual and physical inspection
Inspect the following items :
- the control module grounds for being clean, tight, and in their proper location.
- the vacuum hoses for splits, kinks, and proper connections.
- the wiring for the following items:
- Proper connections.
- Pinches
- Cuts
- the following symptom tables contain groups of possible causes for each symptom. The order of these procedures is not important. If the scan tool readings do not indicate the problems, then proceed in a logical order, easiest to inspect or most likely to cause first.
verify customer's concern
Locate the correct symptom table. Inspect the items indicated under that symptom from the following symptom tables:
- intermittent conditions
- hard start
- surges/chuggles
- lack of power, sluggishness, or sponginess
- fuel knock/combustion noise
- hesitation, sag, stumble
- cuts out, misses
- poor fuel economy
- rough, unstable, or incorrect idle and stalling
- excessive smoke
intermittent conditions
inspections | action |
definition : the condition is not currently present but is indicated in dtc history. definition : or definition : there is a customer concern, but the symptom cannot currently be duplicated, if the condition is not dtc related. |
preliminary | - refer to "Important Preliminary Inspection Before Starting" in Symptoms - Engine Controls.
- the fault must be present to locate a problem using the dtc table. If a fault is intermittent, the use of DTC tables may result in the replacement of good parts.
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visual/physical | this step is an important aid for locating a condition without extensive testing. Perform a thorough visual and physical inspection of the following components: - wiring harness for damage or cuts
- a misrouted harness that is too close to high voltage or high current devices such as the following:
- vacuum hoses for the following conditions:
- Proper routing
- Proper connections
- Splits in the hose or the connections
- Kinks
- the control module and body grounds are clean and tight.
- battery connections are clean and tight
- charging system for proper operation.
|
harness/connector test | many intermittent open or shorted circuits come and go with harness and connector movement caused by vibration, engine torque, bumps and rough pavement, etc. Test for this type of condition by performing the applicable procedure from the following list: - move the related connectors and wiring while monitoring the appropriate scan tool data.
- move the related connectors and wiring with the component commanded on and off, with the scan tool. Observe the components operation.
- with the engine running, move the related connectors and wiring while monitoring engine operation.
if harness or connector movement affects the data displayed, the component and system operation, or the engine operation, inspect and repair the harness or connections as necessary. |
electrical connections or wiring | poor electrical connections and terminal tension or wiring faults cause most intermittents. Perform a careful inspection of the suspected circuit for the following: - inspect for incorrect mating of the connector halves, or terminals not fully seated in the connector body, backed-out.
- inspect for improperly formed or damaged terminals. Test for incorrect terminal tension.
- inspect for poor terminal to wire connections including terminals crimped over insulation. This requires removing the terminal from the connector body.
- inspect for corrosion or water intrusion. Pierced or damaged insulation can allow moisture to enter the wiring. The conductor can corrode inside the insulation with little visible evidence. Look for swollen and stiff sections of wire in the suspect circuits.
- inspect for wires that are broken inside the insulation.
- inspect the harness for pinched, cut, or rubbed through wiring.
- make sure the wiring does not come in contact with hot exhaust components.
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control module power and grounds | poor power or ground connections can cause widely varying symptoms. - test all control module power circuits. Many vehicles have multiple circuits supplying power to the control module. Inspect connections at the control module connectors, fuses, and any intermediate connections between the power source and the control module or component. A test lamp or a DMM may indicate that voltage is present, but neither tests a circuits ability to carry sufficient current. Ensure that the circuit can carry the current necessary to operate the component.
- test all control module ground and system ground circuits. The control module may have multiple ground circuits. Other components in the system may have separate grounds that may also need to be tested. Make sure the ground connections are clean and tight at the grounding point. Inspect the connections at the component and in splice packs, where applicable. Ensure that the circuit can carry the current necessary to operate the component.
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temperature sensitivity | - an intermittent condition may occur only when the component is cold, or only when the component is hot. The heat that affects the circuit can be engine generated or due to a poor connection in the circuit or a high electrical load.
- information from the customer may help to determine if the trouble follows a pattern that is temperature related. The Freeze Frame/Failure Records or Snapshot data may help with this type of intermittent condition, where applicable.
- if the intermittent is related to heat, review the data for a relationship with the following:
- High ambient temperatures
- Underhood/engine generated heat
- Circuit generated heat due to a poor connection, or high electrical load
- Higher than normal load conditions (towing, etc.)
- if the intermittent is related to cold, review the data for the following:
- Low ambient temperatures
- In extremely low temperatures, ice may form in a connection or component. Inspect for water intrusion.
- The condition only occurs on a cold start.
- The condition goes away when the vehicle warms up.
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electromagnetic interference (emi) and electrical noise | some electrical components and circuits are sensitive to electromagnetic interference (emi) or other types of electrical noise. Inspect for the following conditions: - a misrouted harness that is too close to high voltage and high current devices such as, motors, generator, etc. These components may induce electrical noise on a circuit that could interfere with normal circuit operation.
- electrical system interference caused by a malfunctioning relay, control module driven solenoid, or switch. They can cause a sharp electrical surge. Normally, the problem will occur when the malfunctioning component is operating.
- incorrect installation of non-factory, aftermarket, add-on accessories such as lights, 2-way radios, amplifiers, electric motors, remote starters, alarm systems, cell phones, etc.
- test for an open diode across the a/c compressor clutch and for other open diodes. Some relays may contain a clamping diode or resistor.
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incorrect control module programming | - there are only a few situations where reprogramming a control module is appropriate:
- A new control module is installed.
- Revised software/calibration files have been released for this vehicle.
Important : DO NOT reprogram the control module with the SAME software/calibration files that are already present in the control module. This is not an effective repair for any type of driveability problem. - verify that the control module contains the correct software/calibration. If incorrect programming is found, reprogram the control module with the most current software/calibration.
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duplicating failure conditions | if the previous tests were not successful, attempt to duplicate and/or capture the failure conditions.Freeze Frame/Failure Records data, where applicable, contains the conditions that were present when the DTC set. - review and record the freeze frame/failure records data.
- clear any dtcs with a scan tool.
- turn off the key and wait 15 seconds.
- operate the vehicle under the same conditions that were noted in freeze frame/failure records. The vehicle must also be operating within the Conditions for Running the DTC. Refer to Conditions for Running the DTC in the supporting text of the DTC being diagnosed.
- monitor dtc status for the dtc being tested. The scan tool will indicate Ran when the enabling conditions have been satisfied long enough for the DTC to run. The scan tool will also indicate whether the DTC passed or failed.
an alternate method is to drive the vehicle with a dmm connected to a suspected circuit. An abnormal reading on the DMM when the problem occurs may help you locate the problem. |
scan tool snapshot | the scan tool can be set up to take a snapshot of the parameters available via serial data. The Snapshot function records live data over a period of time. The recorded data can be played back and analyzed. The scan tool can also graph parameters singly or in combinations of parameters for comparison. The snapshot can be triggered manually at the time the symptom is noticed or set up in advance to trigger when a DTC sets. an abnormal value captured in the recorded data may point to a system or component that needs to be investigated further.Refer to the scan tool user instructions for more information on the Snapshot function. |
hard start
inspections | action |
definition : the engine cranks ok, but does not start for a long time. The engine does eventually run, or may start but immediately stops. |
preliminary inspection | |
sensor inspection | - inspect the engine coolant temperature (ect) sensor. Use the scan tool to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the ECT sensor circuit or the sensor itself.
- turn on the ignition with the engine off. Observe the actual fuel rail pressure with a scan tool. The actual fuel rail pressure (FRP) signal voltage should be about 0.5V. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor.
- inspect the camshaft position (cmp) sensor and crankshaft position (ckp) sensor for proper mounting and/or a bad connection.
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fuel system inspection | - inspect the fuel pressure regulator circuits for an intermittent short to ground.
- inspect the fuel supply to the fuel injection pump.
- inspect for a restricted fuel filter.
- inspect for air in the fuel system.
- inspect for external fuel leaks.
- inspect for high engine oil level.
- inspect for low fuel pressure.
- inspect the fuel tank cap vent for proper operation.
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electrical system inspection | inspect for a slow cranking speed. |
air intake system inspection | - inspect the air cleaner and air intake ducts for a restrictions or leaks.
- inspect for a restriction in turbocharger inlet duct.
- inspect for a restriction or a leak in the intake manifolds.
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exhaust system inspection | inspect the exhaust system for a possible restriction. |
engine mechanical inspection | inspect the engine for the following conditions: - improper valve timing
- bent pushrods
- worn rocker arms
- low engine compression
- broken or weak valve springs
- worn camshaft lobes
|
additional inspection | - inspect for an intermittent ckp signal. Refer to Intermittent Conditions.
- inspect the service bulletins for control module software updates.
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surges/chuggles
inspections | action |
definition : the engine has a power variation under a steady throttle or cruise. The vehicle seems to speed up and slow down with no change in the accelerator pedal. |
preliminary inspection | - refer to Symptoms - Engine Controls.
- ensure the driver understands the torque converter clutch (tcc) operation.
- ensure the driver understands the a/c compressor operation.
- use the scan tool to ensure the vehicle speed sensor (vss) reading matches the speedometer. This excludes vehicles with electronic transmissions where some variation between VSS and the speedometer is normal.
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sensor inspection | - turn on the ignition with the engine off. Observe the actual fuel rail pressure with a scan tool. The actual fuel rail pressure signal voltage should be about 0.5V. If it is not, inspect for high resistance in the fuel rail pressure (FRP) sensor circuits or the FRP sensor.
- test for an intermittent frp sensor signal by wiggling the harness between the sensor and the engine control module (ecm) with the ignition on and the engine off, while monitoring the parameter with a scan tool.
- inspect the camshaft position (cmp) sensor and crankshaft position (ckp) sensor for a proper mounting and/or a bad connection.
|
fuel system inspection | - inspect the fuel supply system vacuum while the problem exists.
- inspect for a sticking fuel pressure regulator. The symptom for this condition will be an idle surge of at least 100 RPM. This surge will be from 50 RPM above Desired Idle Speed to 50 RPM below Desired Idle Speed.
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additional inspection | - inspect the control module grounds for being clean, tight, and in their proper locations.
- inspect the generator output voltage. Repair if less than 9 volts or more than 16 volts.
- inspect the tcc operation.
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lack of power, sluggishness, or sponginess
inspections | action |
definition : the engine delivers less than expected power. There is little or no increase in speed when partially applying the accelerator pedal. |
preliminary inspection | - refer to Symptoms - Engine Controls.
- inspect for fuel filters. Aftermarket fuel filters may restrict fuel flow.
- compare the vehicle with a similar unit. Ensure the vehicle has an actual problem.
- remove the air filter and check for dirt, or for air ducts being plugged or leaking. Repair or replace as necessary.
- inspect for a proper transmission operation.
- inspect the engine oil level and quality.
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sensor inspection | - inspect the camshaft position (cmp) sensor and crankshaft position (ckp) sensor for proper mounting and/or a bad connection.
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fuel system inspection | - inspect the fuel supply to the fuel injection pump
- observe the actual vs desired fuel rail pressure with a scan tool, with the engine idling.
- inspect the engine speed signal circuit for high resistance.
- inspect for restricted or plugged fuel injectors.
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exhaust system checks | - inspect the exhaust system for a possible restriction.
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air intake system checks | - inspect for an air leak or restriction in the air inlet ducts or the intake manifold.
- inspect for an air leak or restriction in the charge air cooler.
- inspect for a worn or damaged turbo charger turbine wheel, shaft or compressor wheel.
- inspect for a skewed mass air flow (maf) sensor.
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engine mechanical check | inspect the engine for the following: - low compression
- improper valve timing
- improper or worn camshaft
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additional checks | - inspect the control module grounds for being clean, tight, and in their proper location.
- inspect the torque converter clutch (tcc) operation.
- inspect the air conditioning system for proper operation.
- inspect the generator output voltage.
|
fuel knock/combustion noise
inspections | action |
definition : a mild to severe ping, usually worse under acceleration. The engine makes sharp metallic knocks that change with the accelerator pedal depressed. |
preliminary checks | - refer to Symptoms - Engine Controls.
- ensure the vehicle has an actual problem
- inspect for smoke associated with the combustion noise. Refer to Fuel System Checks below.
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cooling system checks | - inspect for obvious overheating problems.
- inspect for a low engine coolant level.
- inspect for any restricted air flow through the radiator.
- inspect for a malfunctioning or incorrect thermostat.
- inspect for a correct coolant solution. The solution should be a 50/50 mix of anti-freeze and water.
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sensor inspection | - inspect the engine coolant temperature (ect) sensor by using the scan tool in order to compare the ect with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, check for a high resistance in the coolant sensor circuit or the sensor itself.
- turn on the ignition with the engine off. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP signal voltage should be about 0.5V. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor.
- inspect for an intermittent crankshaft position (ckp) sensor signal. Refer to Intermittent Conditions.
- inspect the camshaft position (cmp) sensor and crankshaft position (ckp) sensor for proper mounting and/or a bad connection.
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fuel system checks | - if excessive smoke is present, check for a stuck open fuel injector.
- inspect for plugged fuel injectors.
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engine mechanical checks | - inspect for incorrect basic engine parts such as cam, heads, pistons, etc.
- inspect for any excessive oil entering combustion chamber.
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additional checks | - review the service bulletins for control module software updates.
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hesitation, sag, stumble
inspections | action |
definition : the vehicle has a momentary lack of response when pushing down on the accelerator. The condition can occur at any vehicle speed. The condition is usually most severe when trying to make the vehicle move from a stop. If severe enough, the condition may cause the engine to stall. |
preliminary inspection | |
fuel system inspection | - inspect the fuel supply system vacuum.
- inspect for water contamination in the fuel.
- perform the fuel injector balance test.
- inspect for high pressure fuel supply system vacuum after a cold start or during moderate or full throttle acceleration.
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sensor inspection | - turn on the ignition with the engine off. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP signal voltage should be about 0.5V. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor.
- test for an intermittent frp sensor signal by wiggling the harness between the sensor and the engine control module (ecm) with the ignition on and the engine off, while monitoring the parameter with a scan tool.
- inspect for an intermittent crankshaft position (ckp) sensor signal. Refer to Intermittent Conditions.
- inspect the camshaft position (cmp) sensor and crankshaft position (ckp) sensor for proper mounting and/or a bad connection.
|
additional inspection | - review the service bulletins for control module software updates.
- inspect the generator output voltage.
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cuts out, misses
inspections | action |
definition : a constant jerking that follows the engine speed, usually more pronounced as the engine load increases which is not normally felt above 1500 rpm or 48 km/h (30 mph). The exhaust has a steady spitting sound at idle, low speed, or hard acceleration for the fuel starvation that can cause the engine to cut-out. |
preliminary inspection | |
sensor inspection | - inspect for an intermittent crankshaft position (ckp) sensor signal.
- inspect the camshaft position (cmp) sensor and crankshaft position (ckp) sensor for proper mounting and/or a bad connection.
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engine mechanical inspection | - perform the engine compression test.
- inspect the engine for the following conditions:
- Improper valve timing
- Bent pushrods
- Worn rocker arms
- Worn camshaft lobes
- Broken or weak valve springs
- inspect the intake and exhaust manifold passages for casting flash.
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fuel system inspection | - inspect the fuel system for a plugged fuel filter, high vacuum, air in the fuel system, etc
- inspect for water contamination in the fuel.
- inspect the fuel injectors for proper operation.
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poor fuel economy
inspections | action |
definition : fuel economy, as measured by actual road tests and several tanks of fuel, is noticeably lower than expected. Also, the economy is noticeably lower than it was on this vehicle at one time, as previously shown by actual road tests. |
preliminary inspection | - refer to Symptoms - Engine Controls.
- inspect the air filter for dirt or being plugged.
- inspect for an air leak in the charge air cooler.
- inspect the air conditioning system for proper operation.
- inspect the tires for correct air pressure.
- inspect the driving habits of the owner.
- are heavy loads being carried?
- suggest to the owner to fill the fuel tank and inspect the fuel economy.
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sensor inspection | - inspect for an intermittent crankshaft position (ckp) sensor signal.
- inspect the camshaft position (cmp) sensor and crankshaft position (ckp) sensor for proper mounting and/or a bad connection.
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fuel system inspection | - inspect the fuel type and quality.
- inspect the fuel system vacuum.
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cooling system inspection | - inspect the engine coolant level.
- inspect the engine thermostats for always being open or for the wrong heat range.
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additional inspection | - inspect the transmission for proper operation.
- inspect the torque converter clutch (tcc) operation. When the TCC is commanded ON, a scan tool should indicate an RPM drop.
- inspect the service bulletins for control module software updates.
- inspect the brake for proper operation.
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rough, unstable, or incorrect idle and stalling
inspections | action |
definition : engine runs unevenly at idle. If severe, the engine or vehicle may shake. Engine idle speed may vary in RPM. Either condition may be severe enough to stall the engine. |
preliminary inspection | - refer to important preliminary inspection before starting in Symptoms - Engine Controls.
- search for bulletins.
- inspect the vehicle for factory or aftermarket accessories that may contact the body and chassis. A grounding out condition may simulate a misfire or rough run concern.
- inspect the engine control module (ecm) grounds for being clean, tight, and in the proper locations.
- remove and inspect the air filter element for dirt or for being restricted. Replace as necessary.
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sensor inspection | - turn on the ignition with the engine off. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP signal voltage should be about 0.5V. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor.
- test for an intermittent frp sensor signal by wiggling the harness between the sensor and the ecm with the ignition on and the engine off, while monitoring the parameter with a scan tool.
- inspect for an intermittent crankshaft position (ckp) sensor signal.
- inspect the camshaft position (cmp) sensor and the crankshaft position (ckp) sensor for a proper mounting and/or a bad connection.
- inspect for proper crankcase ventilation.
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fuel system inspection | - perform the fuel injector balance test.
- inspect for a restricted fuel filter.
- inspect for a contaminated fuel condition.
- inspect for a sticking fuel pressure regulator. The symptom for this condition will be an idle surge of at least 100 RPM. This surge will be from 50 RPM above Desired Idle Speed to 50 RPM below Desired Idle Speed.
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engine mechanical inspection | - inspect engine mechanical for the following:
- Inspect the cylinder compression
- Sticking or leaking valves
- Worn camshaft lobes
- Valve timing
- Bent push rods
- Worn rocker arms
- Broken valve springs
- Excessive oil in the combustion chamber
- inspect the following components for incorrect basic engine parts:
- Camshaft
- Cylinder heads
- Pistons, connecting rods, or bearings
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additional inspection | - inspect the following components of the exhaust system for possible restrictions:
- The exhaust system for damaged or collapsed pipes
- The exhaust manifold for a collapsed inner wall
- The mufflers for heat distress or possible internal failure
- electromagnetic interference (emi) on the reference circuit can cause an engine miss condition. A scan tool can usually detect EMI by monitoring the engine RPM. A sudden increase in RPM, with little change in actual engine RPM change, indicates that EMI is present. If a problem exists, inspect routing of high voltage components, such as fuel injector wiring, near the sensor circuits.
- inspect the park neutral position (pnp) switch circuit.
- inspect for faulty engine mounts.
- inspect the intake manifold and the exhaust manifold passages for casting flash.
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excessive smoke (gray or blue)
inspections | action |
definition : gray or blue smoke under load, idle or start up hot or cold. |
preliminary inspection | |
fuel system inspection | - observe the actual vs. desired fuel rail pressure with a scan tool, with the engine running.
- inspect the fuel injectors.
|
sensor inspection | - inspect the engine coolant temperature (ect) sensor. Use the scan tool in order to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the coolant sensor circuit or the sensor itself.
- turn on the ignition with the engine off. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP signal voltage should be about 0.5V. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor.
|
air intake system inspection | - inspect the air cleaner and the air intake ducts for restriction.
- inspect for contamination of the mass air flow (maf) sensor.
- inspect for a restriction in the turbocharger charge air cooler.
- inspect for a restriction in the intake manifold.
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engine mechanical inspection | - perform a cylinder leakage test.
- perform the engine compression test.
- inspect for incorrect basic engine parts such as the cam, the heads, the pistons, piston rings, and valves.
- inspect for excessive oil entering the combustion chamber.
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turbocharger inspection | inspect for leaking seals in the turbocharger. |
excessive smoke (white)
inspections | action |
definition : white smoke under load, idle or start up hot or cold. |
preliminary inspection | |
fuel system inspection | - if excessive smoke is present, inspect for a stuck open fuel injector.
- inspect for the plugged fuel injectors.
|
sensor inspection | - inspect the engine coolant temperature (ect) sensor. Use the scan tool in order to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the coolant sensor circuit or the sensor itself.
- turn on the ignition with the engine off. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP signal voltage should be about 0.5V. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor.
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air intake system inspection | - inspect the air cleaner and the air intake ducts for restriction.
- inspect for a restriction in the turbocharger charge air cooler.
- inspect for a restriction in the intake manifold.
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engine mechanical inspection | - inspect for incorrect basic engine parts such as the cam, the heads, the pistons, etc.
- inspect for coolant entering the combustion chamber.
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excessive smoke (black)
inspections | action |
definition : black smoke under load, idle or start up hot or cold. |
preliminary inspection | |
fuel system inspection | - observe the actual vs. desired fuel rail pressure with a scan tool, with the engine running.
- inspect the fuel injectors.
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sensor inspection | - inspect the engine coolant temperature (ect) sensor. Use the scan tool in order to compare the ECT with the ambient air temperature on a cold engine. If the coolant temperature reading is more than 5 degrees more or less than the ambient air temperature on a cold engine, inspect for a high resistance in the coolant sensor circuit or the sensor itself.
- turn on the ignition with the engine off. Observe the actual fuel rail pressure (FRP) with a scan tool. The actual FRP signal voltage should be about 0.5V. If it is not, inspect for high resistance in the FRP sensor circuits or the FRP sensor.
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air intake system inspection | - inspect for a restriction in the air cleaner or the air intake ducts.
- inspect for a restriction in the turbocharger charge air cooler.
- inspect for a restriction in the intake manifold.
- inspect for an air leak in the charge air cooler.
- inspect for an air leak in the air ducts between the turbocharger and the intake manifold.
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engine mechanical inspection | - inspect for incorrect basic engine parts such as the cam, the heads, the pistons, etc.
- inspect for excessive oil entering the combustion chamber.
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malfunction indicator lamp (mil) inoperative
circuit description
Ignition voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.
test description
The numbers below refer to the step numbers on the diagnostic table.
- This step determines if the condition is with the MIL control circuit or the ECM.
- This step determines if a voltage is constantly being applied to the control circuit.
malfunction indicator lamp (mil) inoperative
| step | action | value(s) | yes | no |
| 1 | did you perform the diagnostic system check? | - | go to step 2 | |
| 2 | - start the engine.
- command the malfunction indicator lamp (mil) on and off with a scan tool.
does the mil turn on and off when commanded with a scan tool? | - | | go to step 3 |
| 3 | - turn off the ignition.
- disconnect the engine control module (ecm).
- turn on the ignition, with the engine off.
- connect a 3-amp fused jumper wire between the mil control circuit and a good ground.
- observe the mil.
is the mil illuminated? | - | go to step 7 | go to step 4 |
| 4 | did the fuse in the jumper wire open? | - | go to step 8 | go to step 5 |
| 5 | - remove the i/p.
- test the mil control circuit for an open between the ecm and the i/p.
did you find and correct the condition? | - | | |
| 6 | test for an intermittent and for a poor connection at the i/p. did you find and correct the condition? | - | | |
| 7 | test for an intermittent and for a poor connection at the ecm. did you find and correct the condition? | - | | |
| 8 | repair the short to voltage in the mil control circuit. did you complete the repair? | - | | - |
| 9 | inspect the mil for an open. If the lamp is open, replace the lamp. did you find and correct the condition? | - | | |
| 10 | replace the instrument panel cluster. did you complete the replacement? | - | | - |
| 11 | replace the ecm. did you complete the replacement? | - | | - |
| 12 | operate the system in order to verify the repair. did you correct the condition? | - | system ok | go to step 2 |
malfunction indicator lamp (mil) always on
circuit description
Ignition voltage is supplied directly to the malfunction indicator lamp (MIL). The engine control module (ECM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.
test description
The numbers below refers to the step number on the diagnostic table.
- This step determines if the condition is with the MIL control circuit or the ECM.
malfunction indicator lamp (mil) always on
| step | action | value(s) | yes | no |
| 1 | did you perform the diagnostic system check? | - | go to step 2 | |
| 2 | Important : Do not perform this diagnostic if there is a DTC set. - turn off the ignition.
- disconnect the engine control module (ecm).
- turn on the ignition, with the engine off.
- observe the malfunction indicator lamp (mil).
is the mil illuminated? | - | go to step 3 | go to step 5 |
| 3 | - remove the instrument panel (i/p).
- test the mil control circuit for a short to ground between the ecm and the i/p.
did you find and correct the condition? | - | go to step 6 | go to step 4 |
| 4 | replace the i/p. did you complete the replacement? | - | | - |
| 5 | replace the ecm. did you complete the replacement? | - | | - |
| 6 | operate the system in order to verify the repair. did you correct the condition? | - | system ok | go to step 2 |
