Engine Controls - Basic Diagnostic Procedures: Diagnosis Chevrolet Silverado 2500

VISUAL INSPECTION

Visually inspect all electrical wiring. Look for chafed, stretched, cut or pinched wiring. Ensure electrical connectors fit tightly and are not corroded. Ensure vacuum hoses are properly routed and not pinched or cut. If necessary, see appropriate VACUUM DIAGRAMS article to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Diagnosis

1. Start engine and allow it to reach normal operating temperature. Increase engine speed to 2000-2500 RPM and note gauge. If reading exceeds 1.25 psi (.09 kg/cm 2 ), exhaust system is restricted.
2. Check exhaust system for collapsed pipe, heat distress and possible internal muffler failure. If none of these conditions exist, check for restricted catalytic converter. Replace as necessary.

NO-START DIAGNOSIS

Note. For terminal and circuit identification, see WIRING DIAGRAMS article.

1. Definition No-start is defined as engine cranks properly, but does not start. Engine may fire a few times.

Diagnostic Aids

Check for proper Idle Air Control (IAC) operation. See SYSTEM & COMPONENT TESTING - TRUCKS article. Check for intermittent concerns.

DTCs that may cause a no-start should be diagnosed first

1. "U" type communications DTCs.
2. BCM or ECM PassLock® security system (DTCs P1630, P1631, P1632 or B1372).
3. ECM internal fault DTCs.

With ignition, and engine off, ensure ECT, MAP and TP sensor readings on scan tool are normal. MAP sensor reading should be 14-15 psi (.98-1.1 kg/cm 2 ). The ECT and IAT sensor should be within 10°F (4°C) of each other with vehicle sitting overnight. A skewed sensor may cause a hard or no-start condition.

If no RPM from the CKP sensor is detected, spark and fuel will not be turned on. The signal from the CKP sensor is sent to the ECM. When engine is cranking, the scan tool CKP ACTIVE COUNTER should continuously count up to 255 then reset to zero. Check for flooded engine.

Check the following fuses in the underhood fuse/relay block. These fuses will cause a no-start, if open

1. POWERTRAIN (10A)
2. FUEL PUMP (10A)
3. IGN 1/2 (30A)
4. IGN/INJ (15A)
5. ECM/TCM (10A)
6. ETC (15A)
7. BCM (10A)
8. BCM/Cluster (10A)

DTCs that may cause a no-start should be diagnosed first

1. "U" type communications DTCs (U1000, U1016, U1064, U2105 or U2107).
2. BCM or ECM PassLock® security system DTCs (P1629, P1630, P1631, P1672, B1382, B2947, B2948, B2957, B2958 or B2960).
3. ECM internal fault DTCs.
4. Fuel pump coil circuit DTCs (P0628 or P0629).
5. Crankshaft Position (CKP) sensor circuit DTCs (P0335, P0337 or P0338).

If no CKP sensor signal is detected during engine crank when a valid camshaft sensor signal is received, DTC P0335 will set after a certain period of time. Fuel and spark will not be enabled.

If a MAF circuit fault occurs, the ECM will use engine speed and TP angle to calculate engine airflow. The engine will start if this condition occurs.

Turn ignition on, with engine off. Using scan tool, ensure ECT and MAF sensor voltage readings are normal. MAF sensor voltage should be 0.8-1.2 volts and ECT should be 4°F (2°C) of each other if vehicle has been sitting overnight. A skewed sensor reading may cause a hard or no-start condition.

Check for a flooded engine. To clear a flooded engine, depress accelerator pedal 100% while cranking engine. This engine is not equipped with a clear flood mode that cuts fuel off during engine crank, when flooded.

Ensure main relay is operating correctly. Listen for clicking sound when ignition is turned on. Relay is located in underhood fuse/relay block. Monitor main relay voltage on scan tool. Check the following fuses in the underhood fuse/relay block. These fuses will cause a no-start, if open

1. ECM/TCM (10A)
2. PWR TRAIN (10A)
3. FUEL PUMP (10A)
4. IGN/MAN (10A)
5. ECM/CAM (15A)
6. ENG/IGN (15A)
7. IGNITION (30A)
8. BATT (40A)

Check the following fuses in the instrument panel fuse/relay block. These fuses will cause a no-start, if open

1. BCM/IGN (10A)
2. BCM/CLUSTER (10A)

Inspect for the following conditions

1. Mass Air Flow (MAF) is compared to a calculated mass air flow based upon the manifold absolute pressure (MAP), the throttle position (TP), and the engine RPM readings. A skewed or unresponsive MAP sensor at KEY ON will cause the predicted air flow value to be inaccurate. Compare the MAP and the TP sensor value to that of a known good vehicle.
2. Faulty engine coolant temperature (ECT) sensor. Using a scan tool, compare engine coolant temperature with intake air temperature (IAT) on a completely cool engine. The engine coolant temperature should be within 5°F (3°C) of the intake air temperature. If not, diagnose DTC P0128. See «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) or «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) article.
3. For intermittent condition testing, see «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLESHOOTING - NO CODES - TRUCKS article.

Inspect for the following conditions

1. The Mass Airflow (MAF) is compared to a calculated MAF based upon the Manifold Absolute Pressure (MAP), the Throttle Position (TP), and the engine RPM. A skewed or unresponsive MAP sensor at key ON will cause the predicted airflow value to be inaccurate. Compare the MAP and TP readings to that of a known good vehicle.
2. Inspect for a faulty Engine Coolant Temperature (ECT) sensor. Use a scan tool in order to compare the ECT with the Intake Air Temperature (IAT) on a completely cooled engine. The ECT should be within 5°F (3°C) of the IAT.
3. For an intermittent condition, diagnose by symptom. See «SYMPTOMS (GASOLINE)»(ref-149956-S34497139172002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

If no trouble is found in the fuel pump circuit or the ignition system and the cause of an Engine Cranks But Will Not Run has not been found, check the following conditions

1. Perform the Fuel Injector Coil Test. See FUEL INJECTOR COIL TEST under FUEL SYSTEMS (GASOLINE) in SYSTEM & COMPONENT TESTING - TRUCKS article.
2. An after-market vehicle theft deterrent system could cause a start then stall or a no-start condition.
3. Fouled spark plugs.
4. An Exhaust Gas Recirculation (EGR) valve stuck open.
5. Water or foreign material in the fuel system.
6. A grounded or intermittently grounded Ignition Control (IC) signal circuit.
7. Restricted exhaust system.
8. Check the following ignition components: A grounded tach circuit. Worn distributor cap. Worn distributor rotor. Check ignition wires by lightly spraying them with water in order to identify intermittent no-starts.
9. Check the following mechanical components: Cylinder valve timing. Loose or broken timing chain. Low compression. Worn camshaft lobes. Bent or burned intake or exhaust valves.

The PCM has integrated circuits that are fault protected, therefore, if a circuit has failed, the integrated circuit may not be damaged. If that is the case, then the system will keep the circuit open until the condition has been corrected. Afterwards, reinstall the PCM and check the circuit. Replace the PCM only if the circuit is still inoperative. An intermittent may be caused by any of the following conditions: A poor connection. Rubbed through wire insulation. A broken wire inside the insulation. Thoroughly inspect any circuitry that is suspected of causing the intermittent complaint. Repair as necessary.

If no fault is found and cause of NO-START - ENGINE CRANKS OKAY condition has not been found, check for the following conditions

1. Proper cranking speed, 100 RPMs (cold) or 180 RPMs (hot). Scan tool can be used to check cranking speed by pulling FUEL SOL fuse and monitoring engine speed on scan tool while cranking.
2. Water or foreign material in fuel system.
3. Base engine mechanical fault.
4. If Crankshaft Position (CKP) sensor and optical/fuel temperature sensor are disconnected or malfunctioning at same time, a NO-START - ENGINE CRANKS OKAY condition will exist.

If cause of NO-START - ENGINE CRANKS OKAY symptom has not been found, inspect for following conditions

1. Hard starting only in cold ambient temperatures.
2. Correct cranking speed is 100 RPM cold and 180 RPM hot. A scan tool can be used to inspect cranking speed by pulling Ignition 1 relay and monitoring engine speed on scan tool while cranking.
3. Water or foreign material in fuel system.
4. A base engine mechanical fault.
5. If Crankshaft Position (CKP) sensor and Camshaft Position (CMP) sensor are disconnected or malfunctioning at the same time, a NO-START - ENGINE CRANKS OKAY condition will exist.

Inspect for the following conditions

1. Mass airflow (MAF) is compared to a calculated MAF based upon Manifold Absolute Pressure (MAP), Throttle Position (TP), and engine RPM readings. A skewed or unresponsive MAP sensor at KEY ON will cause predicted airflow value to be inaccurate. Compare MAP and TP sensor values to that of a known good vehicle.
2. Faulty ECT sensor. Using a scan tool, compare engine coolant temperature with Intake Air Temperature (IAT) on a completely cool engine. ECT should be within 5°F (3°C) of intake air temperature. For an intermittent condition, go to «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article.

FUEL SYSTEM PRESSURE TEST (2.2L & 3.0L VUE)

Install a Fuel Pressure Gauge (SA9127E) to fuel service test port. Turn ignition on, with engine off. Using a scan tool, command fuel pump on. Fuel pressure should be 50-60 psi (3.5-4.2 kg/cm 2 ). If fuel pressure is not as specified, diagnose fuel system.

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. Turn ignition on, with engine off. Using scan tool, command fuel pump on. Does fuel pump operate? If yes, go to next step. If no, diagnose fuel pump electrical circuit.
3. Turn ignition off. Turn off all accessories Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S30080408262002110100000) . Install Fuel Pressure Gauge (J-34730-FF). Turn ignition on, with engine off. Command fuel pump ON with scan tool. It may be necessary to command the fuel pump on a few times in order to obtain the highest possible fuel pressure. Observe fuel pressure gauge with fuel pump commanded ON. Is fuel pressure 56-62 psi (386-427 kPa)? If yes, go to next step. If no, go to step 9 .
4. Monitor the fuel pressure gauge for one minute. If fuel pressure decreases more than 5 psi (34 kPa) in one minute, go to step 7 . If fuel pressure does not decrease more than 5 psi (34 kPa) in one minute, go to next step.
5. Relieve fuel pressure to 10 psi (69 kPa). Monitor fuel pressure gauge for 5 minutes. Does fuel pressure decrease by more than 2 psi (14 kPa)? If yes, go to step 17 . If no, go to next step.
6. Operate the vehicle within the conditions to reproduce the original symptoms. Monitor O2 and fuel trim parameters with a scan tool. Do the scan tool parameters indicate a lean condition? If yes, go to step 12 . If no, see «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - 2.2L SONOMA & S10 PICKUP article.
7. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S30080408262002110100000) . Disconnect fuel feed hose from fuel rail. Install Fuel Line Shut-Off Adapter (J-37287) between fuel hose and fuel rail. Open valve on fuel pipe shut-off adapter. Turn ignition on, with engine off. Command fuel pump ON with scan tool. Bleed air from fuel pressure gauge. Command fuel pump ON and then OFF with scan tool. Close fuel feed pipe shut-off valve. Monitor fuel pressure gauge for one minute. Does the fuel pressure remain constant? If yes, go to next step. If no, go to step 15 .
8. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S30080408262002110100000) . Open fuel feed pipe shut-off valve. Raise and support vehicle. Disconnect fuel return pipe from fuel filter. Install Fuel Line Shut-Off Adapter (J-37287) between fuel return pipe and fuel filter. Open fuel return pipe shut-off valve. Turn ignition on, with engine off. Command fuel pump ON with scan tool. Bleed air from fuel pressure gauge. Command fuel pump ON and then OFF with a scan tool. Close the fuel return pipe shut-off valve. Monitor the fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step 16 . If no, go to step 17 .
9. Is the fuel pressure greater than 62 psi (427 kPa)? If no, go to step 11 . If yes, go to next step.
10. Inspect the fuel return pipe and for a restriction. Repair as necessary, then go to step 18 . If repair is not necessary, go to step 16 .
11. Turn ignition off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S30080408262002110100000) . Raise and support vehicle. Disconnect fuel return pipe from fuel filter. Install Fuel Line Shut-Off Adapter (J-37287) between fuel return pipe and fuel filter. Open the valve in the fuel pipe shut-off adapter. Turn ignition on, with engine off. Bleed air from the fuel pressure gauge. Monitor fuel pressure gauge. DO NOT allow fuel pressure to exceed 75 psi (517 kPa). Excessive pressure may damage fuel system. Command fuel pump ON with a scan tool. Slowly close the valve in the fuel return pipe shut-off adapter, while the fuel pump is operating. Does the fuel pressure increase to greater than 62 psi (427 kPa)? If yes, go to step 15 . If no, go to next step.
12. Inspect for a restricted fuel filter or fuel feed pipe. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
13. Inspect the harness connectors and the ground circuits of the fuel pump for poor connections. Did you find and correct the condition? If yes, go to step 18 . If no, go to next step.
14. Remove fuel sender assembly. Inspect fuel pump flex hose for damage, in-tank fuel pump harness connectors for poor connections, fuel strainer for a restriction or fuel tank for contaminants. Did you find and correct the condition? If yes, go to step 18 . If no, go to step 17 .
15. Turn ignition off. Raise fuel rail assembly with fuel pipe connected. Turn ignition on, with engine off. Command fuel pump ON with scan tool. Locate and replace leaking fuel injector. After repairs, go to step 18 .
16. Replace fuel filter. After replacing fuel filter, go to step 18 .
17. Replace fuel sender. After replacing fuel sender, go to next step.
18. Operate the system in order to verify the repair. Did you correct the condition? If yes, system is okay. If no, go to step 3 .

1. Perform OBD system check. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in «SELF-DIAGNOSTICS - 3.4L MONTANA, SILHOUETTE & VENTURE»(ref-140805) or «SELF-DIAGNOSTICS - 3.4L AZTEK & RENDEZVOUS»(ref-140049) . After performing OBD system check, go to next step.
2. Turn ignition off. Turn A/C system off. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S30080408262002110100000) . Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure fitting on fuel rail. Place fuel pressure gauge bleed hose into container. Connect negative battery cable. Turn ignition on. Bleed air from fuel pressure gauge. Using scan tool, command fuel pump on. Observe fuel pressure with fuel pump running. Fuel pressure should be 52-59 psi (3.7-4.1 kg/cm 2 ). If fuel pressure is within specification, go to step 6 . If fuel pressure is not within specification, go to next step.
3. If indicated fuel pressure is greater than 59 psi (4.1 kg/cm 2 ), go to step 14 . If indicated fuel pressure is not greater than 59 psi (4.1 kg/cm 2 ), go to next step.
4. Check fuel system for leaks. Repair as necessary. After repairs, go to step 21 . If no leaks are present, go to next step.
5. If indicated fuel pressure is greater than zero psi, go to step 7 . If indicated fuel pressure is not greater than zero psi, go to step 16 .
6. Monitor fuel pressure. If fuel pressure decreases more than 5 psi (.4 kg/cm 2 ) in 10 minutes, go to next step. If pressure does not decrease more than 5 psi (.4 kg/cm 2 ) in 10 minutes, go to step 9 .
7. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S30080408262002110100000) . Connect Fuel Pipe Shutoff Adapters (J-37287) between fuel feed pipe and fuel return pipe at fuel rail. Open fuel feed and close fuel return valves. Turn ignition on. Bleed air from fuel system. Using scan tool, command fuel pump on and wait for pressure to build. If fuel pressure is constant at 52-59 psi (3.7-4.1 kg/cm 2 ), go to step 19 . If fuel pressure is not as specified, go to next step.
8. Using scan tool, command fuel pump on. With fuel pump running, close fuel feed valve. If fuel pressure is constant, go to step 17 . If fuel pressure is not constant, diagnose fuel injectors. See FUEL INJECTOR BALANCE TEST under FUEL SYSTEMS (GASOLINE) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER article.
9. If fuel pressure is suspected of dropping off during acceleration, cruise or hard cornering, go to next step. If fuel pressure is not suspected of dropping off during acceleration, cruise or hard cornering, go to step 12 .
10. Check in-line fuel filter and fuel feed pipe for restriction. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to next step.
11. Remove fuel sending unit assembly. Check pump strainer for restriction or incorrect installation. Check for leaking fuel pump flex pipe. Ensure fuel pump is correct for vehicle application. Repair as necessary. After repairs, go to step 21 . If no problem is found, go to step 17 .
12. Start engine and allow it to reach normal operating temperature. Observe fuel pressure gauge. If fuel pressure decreases 3-10 psi (.2-.7 kg/cm 2 ), check for intermittent problem. See «INTERMITTENTS»(ref-149956-S33326837422002110400000) in TROUBLE SHOOTING - NO CODES - TRUCKS article. If fuel pressure does not decrease 3-10 psi (.2-.7 kg/cm 2 ), go to next step.
13. With engine idling, disconnect vacuum hose from fuel pressure regulator. Apply vacuum (12 in. Hg) to fuel pressure regulator. If fuel pressure decreases 3-10 psi (.2-.7 kg/cm 2 ), go to step 18 . If fuel pressure does not decrease 3-10 psi (.2-.7 kg/cm 2 ), go to step 19 .
14. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S30080408262002110100000) . Disconnect fuel return pipe. Connect flexible fuel hose to fuel rail return outlet. Place open end of hose into container. Using scan tool, command fuel pump on. Observe fuel pressure gauge. If fuel pressure is 52-59 psi (3.7-4.1 kg/cm 2 ), go to step 20 . If fuel pressure is not as specified, go to next step.
15. Check fuel rail outlet for restriction. Repair as necessary. After repairs, go to step 21 . If no restriction is found, go to step 19 .
16. Check for clogged in-line fuel filter or fuel pump strainer, restricted fuel feed pipe or leaks in fuel pump flex pipe. Repair as necessary. After repairs, go to step 21 . If no problem is found, diagnose fuel pump electrical circuit. See appropriate diagnostic procedure under «NO-START DIAGNOSIS»(ref-149936-S04622626692002110100000) .
17. Replace fuel sending unit assembly. After repairs, go to step 21 .
18. Locate and repair loss of vacuum to fuel pressure regulator. After repairs, go to step 21 .
19. Replace fuel pressure regulator. After repairs, go to step 21 .
20. Repair restriction in fuel return pipe. After repairs, go to next step.
21. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELEASE»(ref-149936-S30080408262002110100000) . Reconnect all fuel system components, leaving fuel pressure gauge installed. Turn ignition on. Using scan tool, command fuel pump on. Monitor fuel pressure with fuel pump running. If fuel pressure is constant at 52-59 psi (3.7-4.1 kg/cm 2 ), system is okay. If fuel pressure is not as specified, go to step 2 .