Engine Controls - Basic Diagnostic Procedures: Other Chevrolet Silverado 2500

Compression

Check engine mechanical condition with compression gauge, vacuum gauge, or engine analyzer. See engine analyzer manual for specific instructions. For compression specifications, see SERVICE & ADJUSTMENT SPECIFICATIONS - TRUCKS article.

Exhaust System Backpressure

Before replacing any components, check exhaust system for restrictions. Use vacuum gauge or low-pressure (0-5 psi) gauge to check exhaust system.

If vacuum gauge is used, connect vacuum gauge hose to intake manifold vacuum port and start engine. Observe vacuum gauge. Partially open throttle and hold steady. If vacuum gauge reading slowly drops after stabilizing, exhaust system should be checked for restriction. If using low pressure gauge, connect gauge in the following manner

1. Check At Oxygen Sensor Remove oxygen sensor. Install backpressure tester in place of oxygen sensor. After test is completed, coat oxygen sensor threads with anti-seize compound before installation.

Preliminary Checks

Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

1. Perform OBD system check. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(ref-138342-S08198199552002040800000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. After performing OBD system check, go to next step.
2. Using scan tool, check for DTCs. If DTCs P0336, P0601, P0602, P1621, P1626, P1631, or P1632 are set, diagnose DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-138342-S05225931112002040800000) in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. If DTCs are not set, go to next step.
3. Using scan tool, monitor CKP activity counter while cranking engine. If counter increments, go to next step. If counter does not increment, diagnose ignition system. See ELECTRONIC IGNITION SYSTEM DIAGNOSIS in SYSTEM & COMPONENT TESTING - TRUCKS article.
4. Turn ignition ON with engine OFF. Probe both sides of the following fuses: ECM B, ECM 1, CLSTR Fuse 11, TBC. Does the test light illuminate on both sides of all the fuses listed? If yes, go to next step. If no, diagnose fused circuit(s). See TESTING FOR SHORT TO GROUND in SYSTEM & COMPONENT TESTING - TRUCKS article.
5. Using scan tool, command fuel pump on. If fuel pump runs, go to next step. If fuel pump does not run, diagnose fuel pump circuit. See FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS in SYSTEM & COMPONENT TESTING - TRUCKS article.
6. Turn ignition OFF. Connect fuel pressure gauge. See «BASIC FUEL SYSTEM CHECKS (GASOLINE)»(ref-149936-S33296934882002110100000) . Using scan tool, command fuel pump on. If fuel pressure is 41-47 psi (248-325 kPa), go to next step. If fuel pressure is not as specified, diagnose fuel system. See «BASIC FUEL SYSTEM CHECKS (GASOLINE)»(ref-149936-S33296934882002110100000) .
7. Connect Spark Tester (J-26792) to No. 1 spark plug wire. Leave other wires connected. Crank engine and check for spark. Repeat for each cylinder. If spark was present at all cylinders, go to next step. If spark was not present at all cylinders, diagnose ignition system. See ELECTRONIC IGNITION SYSTEM DIAGNOSIS in SYSTEM & COMPONENT TESTING - TRUCKS article.
8. Turn ignition OFF. Disconnect an injector connector. Install the Injector Test Lamp (J 34730-405) to the injector connector. Attempt to start the engine. Does the test light flash while the engine is cranking? If yes, go next step. If no, diagnose injector circuit. See FUEL INJECTOR CIRCUIT DIAGNOSIS in SYSTEM & COMPONENT TESTING - TRUCKS article.
9. Inspect for the following conditions; A collapsed air intake duct or restricted air filter element. Spark plugs that are gas fouled or coolant fouled. If the spark plugs are fouled, determine what caused the condition. Engine mechanical conditions, e.g. worn timing chain and gears, low compression, etc. Restricted exhaust system. The engine coolant temperature (ECT) sensor is NOT close to the actual engine temperature. See «DTC P0117: ECT SENSOR CIRCUIT - LOW VOLTAGE»(ref-138342-S05000045932002040800000) or «DTC P0118: ECT SENSOR CIRCUIT - HIGH VOLTAGE»(ref-138342-S40629955002002040800000) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. Compare the Manifold Absolute Pressure (MAP) sensor and throttle position (TP) sensor parameters to another vehicle. The parameters should be close in value. See «DTC P0105: MAP/TP SENSOR CIRCUIT - INSUFFICIENT ACTIVITY»(ref-138342-S24171818082002040800000) under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. Did you find and correct the condition? If yes, go to next step. If no, go to «DIAGNOSTIC AIDS»(ref-149936-S26870785552002110100000) .
10. With a scan tool, clear any DTCs that are set. Attempt to start the engine. Does the engine start and continue to operate? If yes, go to next step. If engine does not start, go to step 2 .
11. Idle the engine. Allow the engine to reach operating temperature. With a scan tool, observe the DTC information. Are any DTCs displayed? If yes, diagnose DTC. See «SELF-DIAGNOSTIC SYSTEM»(ref-138342-S41177419482002040800000) in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. If no, go to next step.
12. With a scan tool, review the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, diagnose DTC. See «SELF-DIAGNOSTIC SYSTEM»(ref-138342-S41177419482002040800000) in SELF-DIAGNOSTICS - 2.2L SONOMA & S10 PICKUP article. If no, system is OK.

NO-START - ENGINE CRANKS OKAY (2.2L VUE)

Note. Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

In order to correctly diagnose a no-start, battery voltage must be greater than 11 volts and engine must be cranking at normal cranking speed (greater than 200 RPM). Fuel level and fuel quality in fuel tank should be checked (do not rely on fuel gauge). When engine is cranked, BCM will check the password from the PassLock® sensor. If password is not received within a certain amount of time or does not match the BCM password, BCM will send a "fuel disable password" to ECM over the CAN bus. The SECURITY indicator light will flash and engine will not start. If the passwords match, BCM will send the password over the CAN bus to ECM. If ECM password does not match the BCM password, or if ECM does not receive a password from BCM, it will allow engine to start and stall within 4 seconds. The SECURITY indicator light will flash for 10 minutes if ECM receives no password, an incorrect password or a disable fuel command. If password to ECM is correct, engine will operate normally.

The password is sent continuously by the BCM to the ECM during run mode. If password becomes lost or incorrect during the drive cycle, vehicle will be allowed to start on succeeding ignition cycles without the aid of PassLock® and the SECURITY indicator light will be on steady. This mode is called fail enable mode.

1. Ensure engine is cranking at normal cranking speed and there is sufficient fuel in fuel tank. Turn ignition on, with engine off. Using scan tool, verify that communications can be established with the BCM and ECM. If scan tool can communicate with BCM and ECM, go to next step. If scan tool does not communicate with BCM and ECM, perform Serial Data Check in Data Link Communication section in the BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
2. Are any BCM and ECM PassLock® security system or communication DTCs set (P1630, P1632 or "U" type DTCs)? If yes, diagnose affected DTC(s). See SELF-DIAGNOSTICS - 2.2L SATURN VUE article. If no, go to next step.
3. Using scan tool, monitor IGNITION 1 voltage in the ECM General Info - Input table. If scan tool reads less than 2 volts, go to step 6 . If scan tool reads more than 2 volts, go to next step.
4. Turn ignition off. Check IGN 1/2 fuse located in underhood fuse/relay block. Replace and retest if fuse is open. Check POWERTRAIN fuse in underhood fuse/relay block. Replace and retest if fuse is open. If affected fuse continues to open, check for short to ground in circuit. See «WIRING DIAGRAMS»(ref-142952) article. If fuses are okay, disconnect ECM harness connector J1. Turn ignition on. Using a DVOM, check voltage between ground and ECM harness connector terminal No. 19 (Pink wire). If ignition voltage is present, go to next step. If ignition voltage is not present, circuit is open. Repair as necessary.
5. Check ground splice for tightness. Check ECM harness connectors for terminal tightness. Repair as necessary. If ground splice and ECM harness connector terminals are okay, replace ECM.
6. Check if any internal ECM DTCs are set. If DTCs are set, diagnose affected DTC(s). See SELF-DIAGNOSTICS - 2.2L SATURN VUE article. If no DTCs are set, go to next step.
7. Using scan tool, monitor CKP ACTIVE COUNTER while cranking engine. If counter increments while cranking engine, go to next step. If counter does not increment while cranking engine, diagnose RPM signal loss. See Crankshaft Position (CKP) sensor diagnosis in SYSTEM & COMPONENT TESTING - TRUCKS article.
8. Using scan tool, monitor CALC COMPRESSION OUTPUT while cranking engine. Is pattern 00000100 or 00001001 displayed on scan tool? If yes, go to next step. If no, diagnose fuel delivery system. See «FUEL SYSTEMS (GASOLINE)»(ref-150429-S03634470992002111300000) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER article.
9. Turn ignition off. Check ING/INJ fuse in underhood fuse/relay block. Replace and retest as necessary. If fuse continues to open when engine is cranked, check for short to ground in circuit. See «WIRING DIAGRAMS»(ref-142952) article. If fuse is okay, disconnect cylinder No. 4 fuel injector harness connector. Connect a Noid Light (J-34730-405) to fuel injector harness connector. Crank engine. If noid light pulses, diagnose fuel delivery system. See «BASIC FUEL SYSTEM CHECKS (GASOLINE)»(ref-149936-S33296934882002110100000) . If noid light does not pulse, repair open in injector circuit.

NO-START - ENGINE CRANKS OKAY (3.0L VUE)

Note. Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

In order to correctly diagnose a no-start, battery voltage must be greater than 11 volts and engine must be cranking at normal cranking speed (greater than 200 RPM). Fuel level and fuel quality in fuel tank should be checked (do not rely on fuel gauge). When engine is cranked, BCM will check the password from the PassLock® sensor. If password is not received within a certain amount of time or does not match the BCM password, BCM will send a "fuel disable password" to ECM over the CAN bus. The SECURITY indicator light will flash and engine will not start. If the passwords match, BCM will send the password over the CAN bus to ECM. If ECM password does not match the BCM password, or if ECM does not receive a password from BCM, it will allow engine to start and stall within 4 seconds. The SECURITY indicator light will flash for 10 minutes if ECM receives no password, an incorrect password or a disable fuel command. If password to ECM is correct, engine will operate normally.

The password is sent continuously by the BCM to the ECM during run mode. If password becomes lost or incorrect during the drive cycle, vehicle will be allowed to start on succeeding ignition cycles without the aid of PassLock® and the SECURITY indicator light will be on steady. This mode is called fail enable mode.

1. Ensure vehicle has adequate fuel and cranking speed is normal. Turn ignition off for 10 seconds. Turn ignition on, with engine off. Using scan tool, verify if communications can be established with the BCM and ECM. Check for DTCs. If scan tool communicates with BCM and ECM, go to next step. If scan tool does not communicate with BCM and ECM, diagnose network communications problem. See appropriate BODY CONTROL MODULES article.
2. Check if there are any BCM/ECM PassLock® security system or communication DTCs present. If BCM DTCs are not present, go to next step. If BCM DTCs are present, see appropriate BODY CONTROL MODULES article.
3. If ECM DTC P0601, P0602, P0603, P0604, P0606 or P0610 is set, diagnose affected DTC(s). See SELF-DIAGNOSTICS - 3.0L SATURN VUE article. If ECM DTC P0601, P0602, P0603, P0604, P0606 or P0610 is not set, go to next step.
4. Check if fuel injector DTCs P0201-P0206 are set. If DTCs P0201-P0206 are not set, go to next step. If DTCs P0201-P0206 are set, check INJ/MAN fuse, located in underhood fuse block. Replace as necessary and retest. If fuse continues to open, check for short on injector circuits. If fuse is okay, repair open in ignition voltage circuit between fuel injectors and underhood fuse block. See «WIRING DIAGRAMS»(ref-142952) article.
5. Check if DTCs P0628 or P0629 is set. If any of the DTC is set, diagnose affected DTC(s). See SELF-DIAGNOSTICS - 3.0L SATURN VUE article. If no DTC is set, go to next step.
6. Using scan tool, monitor ENGINE SPEED while cranking engine. If RPM is not detected, diagnose using DTC P0335 diagnostic procedures. See SELF-DIAGNOSTICS - 3.0L SATURN VUE article. If RPM is detected, go to next step.
7. Turn ignition on, with engine off. Check ENG/IGN fuse in underhood fuse block. Replace as necessary and retest. If fuse continues to open, check for short to ground in ignition circuit. If fuse is okay, go to next step.
8. Using scan tool, perform IGNITION COIL CYL 1-6 test for each individual cylinder while listening closely for spark at appropriate ignition coil. Is spark audible on each cylinder? If yes, go to next step. If no, diagnose ignition system. See «IGNITION SYSTEMS»(ref-150429-S04028583702002111300000) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER article.
9. Connect Fuel Pressure Gauge (SA9127E) to fuel line test port. Using scan tool, command fuel pump relay on for at least 5 seconds. If fuel pressure is 50-60 psi (3.5-4.2 kg/cm 2 ), go to next step. If fuel pressure is not 50-60 psi (3.5-4.2 kg/cm 2 ), diagnose fuel system.
10. Turn ignition on, with engine off. Check for a normal MAF sensor voltage reading (0.8-1.2 volts) and a normal ECT sensor voltage (based on actual engine temperature). Are sensor readings within range? If yes, check for fouled spark plugs, restricted air induction, restricted exhaust, cam timing or engine mechanical failure. If no, diagnose affected sensor using appropriate DTC test procedures (P0101 - MAF or P0116 - ECT). See SELF-DIAGNOSTICS - 3.0L SATURN VUE article.

Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank. Perform OBD system check following any repairs. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE or SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS article.

The Engine Cranks but Does Not Run diagnostic test is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic test directs the service technician to the appropriate system diagnosis. The Engine Cranks but Does Not Run diagnostic test assumes the following: The battery is completely charged, the cranking speed is within specification and there is adequate fuel in the fuel tank.

The Engine Cranks but Does Not Run diagnostic test is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic test directs the service technician to the appropriate system diagnosis. The Engine Cranks but Does Not Run diagnostic test assumes the following: The battery is completely charged, the cranking speed is within specification and there is adequate fuel in the fuel tank.

The Engine Cranks but Does Not Run diagnostic test is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic test directs the service technician to the appropriate system diagnosis. The Engine Cranks but Does Not Run diagnostic test assumes the following: The battery is completely charged, the cranking speed is within specification and there is adequate fuel in the fuel tank.

Ensure the battery is completely charged and the engine cranking speed is within specification. Ensure there is adequate fuel in the fuel tank.

The Engine Cranks but Does Not Run diagnostic test is an organized approach to identifying a condition that causes an engine not to start. The Engine Cranks but Does Not Run diagnostic test directs the service technician to the appropriate system diagnosis. The Engine Cranks but Does Not Run diagnostic test assumes the following: The battery is completely charged, the cranking speed is within specification and there is adequate fuel in the fuel tank.

Ensure that battery condition and engine cranking speed is okay. Ensure that quantity and quality of fuel is okay and glow plug system is operating properly. If diesel fuel system is contaminated with gasoline, purge fuel system. See FUEL SYSTEM CLEANING under FUEL SYSTEMS in appropriate REMOVAL, OVERHAUL & INSTALLATION article.

Ensure batteries are completely charged, cranking speed is within specifications and that there is adequate fuel in fuel tanks.

NO-START - ENGINE CRANKS OKAY (8.1L)

Note. Before performing the following tests, check battery condition, engine cranking speed and for adequate fuel in tank.

Ensure battery is completely charged and that cranking speed is within specifications. Ensure there is adequate fuel in fuel tank

FUEL SYSTEM PRESSURE RELEASE

1. Using scan tool, attempt to communicate with Alternative Fuel Electronic Control Unit (AF ECU). If communication is possible, go to next step. If communication is not possible and system check has been performed, go to step 7 .
2. Read and record any AF ECU DTCs. Go to next step.
3. Clear all AF ECU DTCs. Turn ignition off. Go to next step.
4. Start engine. Ensure vehicle is operating on CNG by noting if fuel indicator light (located on fuel gauge select switch) is off and Natural Gas Operation (NGO) in scan tool data is enabled. If vehicle is operating on CNG, go to next step. If vehicle does not start or is not operating on CNG, go to step 7 .
5. Using scan tool, select High Pressure Lock-Off (HPL) output control. Go to next step.
6. Monitor Fuel Pressure Sensor (FPS) data. While vehicle is operating on CNG, use scan tool to close HPL. If FPS data does not change, go to next step. When engine stalls or changes to gasoline operation, turn ignition off. Remove CNG fuse (20-amp) located in underhood fuse block. Slowly open fuel system fittings to vent remaining pressure.
7. Remove fuel tank cover. Close manual lock down screw on HPL by rotating Allen screw clockwise until fully seated. Go to next step.
8. Turn ignition off. Disconnect negative battery cable. Ensure vehicle is in a well ventilated area, away from sparks and flame. Go to next step.
9. Slowly open fuel line fitting at Low Pressure Lock-Off (LPL) inlet port. Do not remove fitting. Go to next step.
10. If fuel is not venting, relieve fuel line tension by pulling line away from LPL. Go to next step.
11. After fuel has stopped venting, slowly loosen fuel line fitting at High Pressure Regulator (HPR) inlet. Do not remove fitting. Fuel pressure relief is complete when fuel line at HPR inlet stops venting. After repair, replace "O" rings at all fittings that were loosened. Tighten all loosened fittings to specification. Open manual lock down screw counterclockwise to fully seated position.

BASIC FUEL SYSTEM CHECKS (DIESEL)

Note. For diesel fuel system and component diagnosis, see FUEL SYSTEM (DIESEL) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER article.

Loosen retaining bolt on intake manifold sight shield at top of engine. Remove intake manifold sight shield from top of engine. Disconnect negative battery cable. Loosen fuel filler cap. Install Fuel Pressure Gauge (J-34730-1A) on fuel pressure connector of fuel rail. Wrap a shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage. Place gauge bleed hose in container. Open bleed valve to release fuel pressure.

When you turn ON the ignition switch, the Powertrain Control Module (PCM) energizes the fuel pump relay which powers the fuel pump ON. The pump remains ON as long as the engine is cranking or running and the PCM receives reference pulses. If there are no reference pulses, the PCM shuts the fuel pump OFF within 2 seconds after the ignition was switched to the ON position or if the engine stops. An electric fuel pump pumps the fuel through an in-line filter to the fuel meter body assembly. The pump attaches to the fuel sender assembly inside of the fuel tank. The fuel pump provides fuel pressure above what is needed by the fuel injectors. The pressure regulator keeps the fuel available to the injectors at a regulated pressure. Unused fuel returns to the fuel tank by the fuel return pipe.

BASIC IGNITION SYSTEM CHECKS

Note. For additional ignition system and component diagnosis, see IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER article.

IDLE SPEED & IGNITION TIMING (GASOLINE)

Ensure idle speed and ignition timing are set to specifications. For specifications and adjustment procedures, see ON-VEHICLE ADJUSTMENTS - TRUCKS - EXCEPT TRACKER article.

IDLE SPEED & INJECTION PUMP TIMING (DIESEL)

Ensure idle speed and injection pump timing/TDC offset are set to specifications. For specifications and adjustment procedures, see ON-VEHICLE ADJUSTMENTS - TRUCKS - EXCEPT TRACKER article.

SUMMARY

If no faults were found while performing basic diagnostic procedures, or no trouble codes (or only intermittent ones) were found while performing OBD system check, and driveability problems still exist, proceed to TROUBLE SHOOTING - NO CODES - TRUCKS article for diagnosis by symptom (i.e., ROUGH IDLE, NO-START, etc.) or intermittent diagnostic procedures.