MODEL IDENTIFICATION
| Series (1) | Model |
|---|---|
| "C" | 2WD Pickup, Sierra, Suburban, Tahoe & Yukon |
| "G" | (2) RWD Van |
| "K" | 4WD Pickup, Sierra, Suburban, Tahoe & Yukon |
| "P" | Commercial Van/Motorhome |
| (1) Vehicle series is fifth character of VIN. (2) Includes Express, Rally Van & Savana | |
| (1) | Vehicle series is fifth character of VIN. |
| (2) | Includes Express, Rally Van & Savana |
MODEL IDENTIFICATION
INTRODUCTION
Note. Models may use a Powertrain Control Module (PCM) or Vehicle Control Module (VCM). The term PCM will be used in this article to describe all control modules.
Before diagnosing symptoms or intermittent faults, perform steps in the following articles in this section
- F - BASIC TESTING
- G - TESTS W/CODES
Use this article to diagnose driveability problems if a current code is not present or if not equipped with a self-diagnostic system.
Symptom checks are intended to direct technician to malfunctioning component(s) for further diagnosis. A symptom should lead to a specific component or system test, or an adjustment specification. Use intermittent test procedures to locate driveability problems not occurring when vehicle is being tested.
Note. For specific testing procedures, see SYSTEM/COMPONENT TESTS article. To verify specifications, see ADJUSTMENTS or SPECIFICATIONS article.
Note. SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as the Malfunction Indicator Light (MIL).
ENGINE WILL NOT START
| Possible Cause | Correction |
|---|---|
| No voltage to fuel shut-off solenoid | Check electrical connections |
| Restricted air filter | Check and/or replace air filter |
| Faulty glow plugs, relay or PCM | Check and/or replace glow plugs or controls |
| Plugged fuel return system | Remove restrictions |
| No fuel to nozzles | Inspect fuel delivery system |
| No fuel to injection pump | Inspect fuel delivery system |
| Clogged fuel tank filter | Replace filter; see SYSTEM/COMPONENT TESTS article |
| Incorrect or contaminated fuel | Remove and replace fuel |
| Restriction in turbocharger inlet duct (if equipped) | Remove restrictions |
| Incorrect pump timing | See TESTS W/CODES article |
SYMPTOM - ENGINE WILL NOT START
ENGINE STALLS AT IDLE
| Possible Cause | Correction |
|---|---|
| Incorrect slow idle | See TESTS W/CODES article |
| Faulty fast idle solenoid | Replace solenoid; see SYSTEM/COMPONENT TESTS article |
| Plugged fuel return system | Remove restrictions |
| Glow plugs turn off too soon | Check glow plug system; see SYSTEM/COMPONENT TESTS article |
| Limited fuel to injection pump | Check fuel delivery system |
| Air in injection lines to nozzles | Check line fittings |
| Incorrect or contaminated fuel | Remove and replace fuel |
| Faulty injection pump | Replace pump; see REMOVE/INSTALL/OVERHAUL article |
| Fuel shut-off solenoid closes in RUN position | Check solenoid operation; see SYSTEM/COMPONENT TESTS article |
| TCC stuck on | Check brake switch and PCM control |
SYMPTOM - ENGINE STALLS AT IDLE
ENGINE STARTS, IDLES ROUGH WITHOUT UNUSUAL NOISE OR SMOKE
| Possible Cause | Correction |
|---|---|
| Leaking injection line | Check fittings and/or replace line |
| Plugged fuel return line | Remove restrictions |
| Air in lines to nozzles | Check line fittings |
| Air in injection pump | Check pump fittings and pump operation |
| Faulty nozzle | Replace nozzle; see SYSTEM/COMPONENT TESTS article |
| Improper or contaminated fuel | Remove and replace fuel |
| Uneven fuel distribution | Check fuel delivery system |
SYMPTOM - ENGINE STARTS, IDLES ROUGH WITHOUT UNUSUAL NOISE OR SMOKE
SURGE AND/OR CHUGGLE
| Possible Cause | Correction |
|---|---|
| Incorrect pump timing | See TESTS W/CODES article |
| Restricted air filter | Check and/or replace air filter |
| Air in injection lines to nozzles | Check fittings on lines |
| Faulty nozzle | Replace nozzle; see SYSTEM/COMPONENT TESTS article |
| Improperly installed high pressure lines | Remove lines, and reinstall properly |
| Misrouted or kinked vacuum lines | Check lines, and reinstall properly |
| Faulty EGR operation | Check EGR system |
| Faulty charging system | Check alternator output |
| Faulty PCM operation | See TESTS W/CODES article |
| Faulty TCC or shift points | Check transmission operation |
SYMPTOM - SURGE AND/OR CHUGGLE
FUEL LEAKS WITH NO OTHER ENGINE MALFUNCTION
| Possible Cause | Correction |
|---|---|
| Loose or broken fuel line or connection | Check all fuel line fittings, and correct as necessary |
| Internal seal leak in injection pump | Remove and replace injection pump |
SYMPTOM - FUEL LEAKS WITH NO OTHER ENGINE MALFUNCTION
LOW ENGINE POWER
| Possible Cause | Correction |
|---|---|
| Restricted air intake | Remove restrictions |
| Plugged fuel filter | Remove restriction and/or replace filter |
| Faulty PCM operation | See TESTS W/CODES article |
| Improper fuel return system | Check fuel return system |
| Restricted tank-to-pump fuel supply | Check fuel delivery system |
| Incorrect or contaminated fuel | Remove and replace fuel |
| Faulty EGR operation | Check EGR system |
| Worn camshaft or valves Repair as necessary | Check compression and valve lift |
| Nozzle or glow plug compression leaks | Check fittings, and replace as required |
| Plugged nozzle | Remove restriction and/or replace nozzle |
| Worn or damaged turbocharger turbine wheel, shaft or compressor wheel (if equipped) | Repair or replace turbocharger assembly |
| Faulty TCC or shift points | Check transmission operation |
SYMPTOM - LOW ENGINE POWER
"RAPPING" NOISE FROM CYLINDERS
| Possible Cause | Correction |
|---|---|
| Air in fuel system | Check fuel delivery system for leaks |
| Air in high pressure lines | Check fittings for leaks |
| Incorrect pump timing | See TESTS W/CODES article |
| Nozzle sticking in open position | Inspect and/or replace nozzle |
| Low nozzle opening pressure | Check nozzle operation; see SYSTEM/COMPONENT TESTS article |
| Excessive oil entering combustion chamber | Repair internal engine problem |
| Faulty ECT sensor | Check sensor operation; see SYSTEM/COMPONENT TESTS article |
SYMPTOM - "RAPPING" NOISE FROM CYLINDERS
EXCESSIVE NOISE WITH BLACK SMOKE
| Possible Cause | Correction |
|---|---|
| Incorrect pump timing | See TESTS W/CODES article |
| Incorrect pump pressure | Check pump for internal leaks |
| Defective injection pump | Replace injection pump; see SYSTEM/COMPONENT TESTS article |
| Engine coolant temperature sensor reading is 5 degrees greater or less than ambient temperature on a cold engine | Check for high resistance in sensor circuit or sensor |
SYMPTOM - EXCESSIVE NOISE WITH BLACK SMOKE
ENGINE WILL NOT SHUT OFF WITH KEY
| Possible Cause | Correction |
|---|---|
| Injection pump fuel shut-off solenoid does not return to off position | Check solenoid operation; see SYSTEM/COMPONENT TESTS article |
SYMPTOM - ENGINE WILL NOT SHUT OFF WITH KEY
TURBOCHARGER TROUBLE SHOOTING
To trouble shoot following symptoms, refer to appropriate number under PROBABLE CAUSES.
| Symptom | Possible Causes |
|---|---|
| Engine Lacks Power | Clogged air filter element |
| Engine Lacks Power | Obstructed air outlet duct from compressor to intake manifold |
| Engine Lacks Power | Obstructed intake manifold |
| Engine Lacks Power | Air leak in duct from compressor to intake manifold |
| Engine Lacks Power | Air leak at intake manifold-to-engine joint |
| Engine Lacks Power | Obstruction in exhaust manifold |
| Engine Lacks Power | Obstruction in exhaust system |
| Engine Lacks Power | Gas leak in exhaust manifold-to-engine joint |
| Engine Lacks Power | Gas leak in turbine inlet-to-exhaust manifold joint |
| Engine Lacks Power | Engine camshaft timing incorrect |
| Engine Lacks Power | Worn engine piston rings or liners (blow-by) |
| Engine Lacks Power | Internal engine problems (valves, pistons) |
| Engine Lacks Power | Dirt caked on compressor wheel and/or diffused vanes |
| Engine Lacks Power | Damaged turbocharger |
| Engine Lacks Power | Wastegate stuck open |
| Black Smoke | Obstructed air intake duct to turbo compressor |
| Black Smoke | Obstructed air outlet duct from compressor to intake manifold |
| Black Smoke | Obstructed intake manifold |
| Black Smoke | Air leak in duct from compressor to intake manifold |
| Black Smoke | Air leak at intake manifold-to-engine joint |
| Black Smoke | Obstruction in exhaust manifold |
| Black Smoke | Obstruction in exhaust system |
| Black Smoke | Gas leak in exhaust manifold-to-engine joint |
| Black Smoke | Gas leak in turbine inlet-to-exhaust manifold joint |
| Black Smoke | Engine camshaft timing incorrect |
| Black Smoke | Worn engine piston rings or liners (blow-by) |
| Black Smoke | Internal engine problems (valves, pistons) |
| Black Smoke | Dirt caked on compressor wheel and/or diffused vanes |
| Black Smoke | Damaged turbocharger |
| Blue Smoke | Obstructed air intake duct to turbo compressor |
| Blue Smoke | Air leak in duct from compressor to intake manifold |
| Blue Smoke | Air leak at intake manifold-to-engine joint |
| Blue Smoke | Obstruction in exhaust manifold |
| Blue Smoke | Obstructed turbocharger oil drain line |
| Blue Smoke | Obstructed engine crankcase ventilation |
| Blue Smoke | Turbocharger center housing sludged or coked |
| Blue Smoke | Worn engine piston rings or liners (blow-by) |
| Blue Smoke | Internal engine problems (valves, pistons) |
| Blue Smoke | Dirt caked on compressor wheel and/or diffused vanes |
| Blue Smoke | Damaged turbocharger |
| Excessive Oil Consumption | Obstructed air intake duct to turbo compressor |
| Excessive Oil Consumption | Air leak in duct from compressor to intake manifold |
| Excessive Oil Consumption | Air leak at intake manifold-to-engine joint |
| Excessive Oil Consumption | Obstruction in exhaust manifold |
| Excessive Oil Consumption | Obstructed turbocharger oil drain line |
| Excessive Oil Consumption | Obstructed engine crankcase ventilation |
| Excessive Oil Consumption | Turbocharger center housing sludged or coked |
| Excessive Oil Consumption | Worn engine piston rings or liners (blow-by) |
| Excessive Oil Consumption | Internal engine problems (valves, pistons) |
| Excessive Oil Consumption | Dirt caked on compressor wheel and/or diffused vanes |
| Excessive Oil Consumption | Damaged turbocharger |
| Noisy Operation | Clogged air filter element |
| Noisy Operation | Obstructed air intake duct to turbo compressor |
| Noisy Operation | Obstructed air outlet duct from compressor to intake manifold |
| Noisy Operation | Obstructed intake manifold |
| Noisy Operation | Air leak in duct from air cleaner to compressor |
| Noisy Operation | Air leak in duct from compressor to intake manifold |
| Noisy Operation | Air leak at intake manifold-to-engine joint |
| Noisy Operation | Obstruction in exhaust manifold |
| Noisy Operation | Gas leak in turbine inlet-to-exhaust manifold joint |
| Noisy Operation | Gas leak in ducts after turbine outlet |
| Noisy Operation | Dirt caked on compressor wheel and/or diffused vanes |
| Noisy Operation | Damaged turbocharger |
| Cyclic Sound From Turbocharger | Obstructed air intake duct to turbo compressor |
| Cyclic Sound From Turbocharger | Dirt caked on compressor wheel and/or diffused vanes |
| Cyclic Sound From Turbocharger | Damaged turbocharger |
| Oil Leak At Turbine Seal | Obstructed turbocharger oil drain line |
| Oil Leak At Turbine Seal | Obstructed engine crankcase ventilation |
| Oil Leak At Turbine Seal | Turbocharger center housing sludged or coked |
| Oil Leak At Turbine Seal | Worn engine piston rings or liners (blow-by) |
| Oil Leak At Turbine Seal | Internal engine problems (valves, pistons) |
| Oil Leak At Turbine Seal | Dirt caked on compressor wheel and/or diffused vanes |
| Oil Leak At Turbine Seal | Damaged turbocharger |
| Oil Leak At Compressor Seal | Obstructed air intake duct to turbo compressor |
| Oil Leak At Compressor Seal | Obstruction in exhaust manifold |
| Oil Leak At Compressor Seal | Obstruction in exhaust system |
| Oil Leak At Compressor Seal | Gas leak in exhaust manifold-to-engine joint |
| Oil Leak At Compressor Seal | Gas leak in turbine inlet-to-exhaust manifold joint |
| Oil Leak At Compressor Seal | Obstructed turbocharger oil drain line |
| Oil Leak At Compressor Seal | Obstructed engine crankcase ventilation |
| Oil Leak At Compressor Seal | Turbocharger center housing sludged or coked |
| Oil Leak At Compressor Seal | Worn engine piston rings or liners (blow-by) |
| Oil Leak At Compressor Seal | Internal engine problems (valves, pistons) |
| Oil Leak At Compressor Seal | Dirt caked on compressor wheel and/or diffused vanes |
| Oil Leak At Compressor Seal | Damaged turbocharger |
SYMPTOM - TURBOCHARGING TROUBLE SHOOTING
INTERMITTENT PROBLEM DIAGNOSIS
Intermittent fault testing requires duplication of circuit or component failure in order to identify fault. These procedures may lead to computer recording a fault code which may help diagnosis.
If problem vehicle does not produce fault codes, use a DVOM to monitor voltage or resistance values while attempting to reproduce conditions which will create an intermittent fault. A change in status on DVOM indicates a fault has been located.
When using a voltmeter to pinpoint faults, monitor voltage reading with ignition on or vehicle running. A change in status on voltmeter while performing test procedure indicates area of fault. See TEST PROCEDURES under INTERMITTENTS.
When using an ohmmeter to detect problems in circuit, monitor circuit resistance (ohms) with ignition switch in OFF position or with battery disconnected. A change in ohmmeter reading while performing test procedure indicates area of fault. See TEST PROCEDURES under INTERMITTENTS.
Intermittent Simulation
Use following methods to reproduce conditions causing intermittent.
- Apply light vibration to components.
- Heat component.
- Wiggle or bend wiring harness.
- Spray component with water.
- Remove/apply vacuum supply source.
Monitor circuit/component voltage or resistance while attempting to simulate intermittent. If vehicle is running, monitor for self-diagnostic codes. Use test results to identify faulty component or circuit.
Symptom Definition
Malfunction Indicator Light (MIL) comes on but does not stay on. A stored code may or may not exist.
Possible Causes & Corrections
Use following procedures to determine possible causes of intermittent Malfunction Indicator Light (MIL) operation.
- Check for poor mating of one connector to another. Terminals may not be fully seated. Check for improperly formed or damaged terminals. Check wire-to-terminal connections.
- Check for poor connection from ignition coil to ground or arcing at spark plug wires or plugs.
- Check wire from Malfunction Indicator Light (MIL) to PCM for short to ground.
- Check wire from Data Link Connector (DLC) test terminal for intermittent short to ground.
- Check for poor connections in PCM ground terminals.
- Check for electrical system interference caused by defective relay, PCM-driven solenoid or switch, which may cause sharp electrical surge. This type of problem will normally occur when faulty component is operated.
- Check for aftermarket parts which may not have been produced to manufacturers' specifications. Solenoids without original-equipment diodes for circuit protection or voltage regulator using transistors instead of silicone-chip circuitry may cause voltage surges (up to 300 volts) in PCM wiring, causing temporary PCM shutdown. PCM shutdown is a normal response to system overvoltage (over 16 volts on most models). PCM repowers when condition ceases to exist. A rapid shutdown and repower could cause a flickering Malfunction Indicator Light (MIL) with no codes set in memory.
- Check for improper installation of electrical accessories such as auxiliary lights or 2-way radios.
- Ensure EST wires are kept away from spark plug wires, distributor wires, distributor housing, ignition coil and generator. Ensure ground wire from PCM to distributor or ignition module is connected to a good ground.
- Check for intermittent short to ground on terminal "B" (diagnostic enable) of Data Link Connector (DLC) or in Malfunction Indicator Light (MIL) circuit.
- On vehicles not equipped with a driver information center, use scan tester to check for intermittent wiring problem. See SCAN TESTER USAGE in appropriate TESTS W/CODES article.
See also:
• TEST PROCEDURES