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Engine Controls - Basic Diagnostic Procedures Chevrolet Chevy Express H2500

Testing & Diagnostics 2 illustrations ~4316 words

INTRODUCTION

Before proceeding with basic diagnostic procedures, ensure testing procedure is followed, as some systems which may result in a no-start condition may cause a Diagnostic Trouble Codes (DTC) to be stored in the Powertrain Control Module (PCM). See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.

If no-start condition still exists after checking and repairing all DTCs, perform a careful and complete visual inspection. Many problems result from mechanical breakdowns, poor electrical connections or damaged/misrouted vacuum hoses. See VISUAL INSPECTION under PRELIMINARY INSPECTION & ADJUSTMENTS. Before condemning the computerized system, perform each test listed in this article.

Note. Perform all voltage tests with a Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance, unless stated otherwise in test procedure.

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 - EXPRESS & SAVANA article to verify routing and connections. Inspect air induction system for possible vacuum leaks.

Cylinder Compression Pressure

Check engine mechanical condition with compression gauge, vacuum gauge, or engine analyzer. See engine analyzer manual for specific instructions. For compression specifications, see ENGINE COMPRESSION SPECIFICATIONS table. Install and tighten spark plugs to 11 ft. lbs. (15 N.m).

ApplicationSpecification - psi (kPa)
Normal Compression Pressure(1)
Minimum Compression Pressure(1)
Compression Variance(2)
(1) Lowest compression reading should not be less than 70 percent of highest compression reading. No cylinder compression reading should be less than 100 psi (689.5 kPa). (2) Information is not available from manufacturer.
(1)Lowest compression reading should not be less than 70 percent of highest compression reading. No cylinder compression reading should be less than 100 psi (689.5 kPa).
(2)Information is not available from manufacturer.

ENGINE COMPRESSION SPECIFICATIONS

Cylinder Combustion Pressure Leakage

  1. Disconnect negative battery cable. Remove spark plugs. Install Cylinder Head Leakdown Tester (J-35667 A). Measure each cylinder on compression stroke, with both valves closed.
  2. Apply air pressure to cylinder leakdown tester. Record cylinder leakage readings for each cylinder. Any cylinder with 25 percent leakage or more requires service.
  3. Inspect following primary areas in order to properly diagnose a leaking cylinder. If air is heard from intake or exhaust system, remove valve rocker arm cover of suspect cylinder head. Ensure that both valves are closed. Inspect cylinder head for a broken valve spring or remove and inspect suspect cylinder head. If air is heard from crankcase system at crankcase oil filler tube, remove piston from suspect cylinder. Inspect piston and connecting rod assembly. Inspect engine block. If bubbles are observed in radiator, remove and inspect both cylinder heads. Inspect engine block.
  4. After performing test, remove leakdown tester. Install spark plugs and reconnect negative battery cable.

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 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.

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 .

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

Preliminary Checks

Before performing following tests, check battery condition, engine cranking speed and for adequate fuel in tank. Perform diagnostic system check following any repairs. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.

  1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. After performing diagnostic system check, go to next step.
  2. Using scan tool, check for DTCs. If DTCs P0230, P0335, P0336, P0601, P0602, P0604, P1626, P1631 or P1683 are set, diagnose affected DTCs. See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. If DTCs are not set, go to next step.
  3. Does scan tool display any Body Control Module (BCM) or Vehicle Theft Deterrent (VTD) DTCs? If yes, diagnose affected DTCs. See appropriate BODY CONTROL MODULES or ANTI-THEFT SYSTEMS article in ACCESSORIES & EQUIPMENT. If no, go to next step.
  4. Attempt to start engine. Observe Engine Speed parameter with a scan tool, while engine is cranking. Does engine speed increment? If yes, go to next step. If no, go to «DISTRIBUTOR IGNITION SYSTEM»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) under IGNITION SYSTEMS.
  5. Monitor ignition 1 signal voltage parameter with a scan tool. (Scheme 2) Is ignition 1 signal voltage parameter at battery voltage? If yes, go to next step. If no, go to step 10.
  6. Command fuel pump on with a scan tool. Does fuel pump turn on? If yes, go to next step. If no, go to «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  7. Turn ignition off. Disconnect a spark plug wire. Install Spark Tester (J-26792) to spark plug wire. Attempt to start engine. Does spark tester spark? If yes, go to next step. If no, go to «DISTRIBUTOR IGNITION SYSTEM»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) under IGNITION SYSTEMS.
  8. Turn ignition off. Install Fuel Pressure Gauge (J-34730-1A). Turn ignition on, with engine off. Command fuel pump on with a scan tool. Is fuel pressure within 55-62 psi (379-427 kPa ) while fuel pump is operating? If yes, go to next step. If no, go to «FUEL SYSTEM DIAGNOSIS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures) under FUEL SYSTEMS.
  9. Inspect for collapsed air intake duct, restricted air filter element, fouled spark plugs, engine mechanical problem or restricted exhaust system. Check if ECT sensor is NOT close to actual engine temperature. Compare MAP/BARO parameters to another vehicle. The parameters should be close in value. Check if TP sensor is stuck in range. Repair as necessary. After repairs, go to step 13.
  10. Test ignition 1 signal voltage circuit for an open or for a short to ground. (Scheme 2) Replace fuse, if necessary. Did you find and correct condition? If yes, go to step 13. If no, go to next step.
  11. Inspect for poor connections at harness connector of PCM. Did you find and correct condition? If yes, go to step 13. If no, go to next step.
  12. Replace PCM. See «REMOVAL & INSTALLATION - CHEVY EXPRESS & SAVANA»(/chevrolet/chevy-express-h2500/2003-2003/remont/removal-installation/#engine-controls-removal-installation-gasoline) article. After replacing PCM, go to next step.
  13. Clear DTCs with a scan tool. Turn ignition off for 30 seconds. Attempt to start engine. Does engine start and continue to run? If yes, go to next step. If no, go to step 2.
  14. Observe Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. If no DTCs are set, system okay.

FUEL SYSTEM PRESSURE RELEASE

WARNINGRemove fuel tank cap and release fuel system pressure before servicing any fuel injection related components. After releasing fuel system pressure, a small amount of fuel may be released when servicing fuel lines, fuel pump or fuel connections. Cover fuel system components with a shop towel before disconnection. DO NOT allow fuel to contact engine or electrical components.
CAUTIONFuel system is under pressure. Pressure must be released prior to servicing fuel system.

Disconnect negative battery terminal. Loosen fuel filler cap to relieve fuel tank vapor pressure. Connect Fuel Pressure Gauge (J-34730-1A) to fuel pressure test port. Wrap a shop towel around fitting while connecting gauge to avoid spillage. Install gauge bleed hose into an approved gasoline container. Open valve on gauge to bleed system pressure. Fuel connections are now safe for servicing. Drain any fuel remaining in gauge into an approved gasoline container.

System Description

The control module enables fuel pump relay when ignition switch is turned on. The control module will disable fuel pump relay within 2 seconds unless control module detects ignition reference pulses. The control module continues to enable fuel pump relay as long as ignition reference pulses are detected. The control module disables fuel pump relay within 2 seconds if ignition reference pulses cease to be detected and ignition remains on.

The fuel tank stores fuel supply. The fuel pump supplies fuel through an in line fuel filter to fuel injection system. The pump provides fuel at a higher rate of flow than is needed by fuel injection system. The fuel pressure regulator maintains correct fuel pressure to fuel injection system. A separate pipe returns unused fuel to fuel tank.

  1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. After performing diagnostic system check, go to next step.
  2. Turn ignition on, with engine off. Command fuel pump relay on with a scan tool. Does fuel pump operate? If yes, go to next step. If no, go to «FUEL PUMP ELECTRICAL CIRCUIT DIAGNOSIS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-control-system-component-tests-43l) under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.
  3. Verify that adequate fuel is in fuel tank before proceeding with this diagnostic. Turn ignition off. Turn off all accessories. Install fuel pressure gauge. Turn ignition on, with engine off. Fuel pump relay may need to be commanded on a few times in order to obtain highest possible fuel pressure. Do not start engine. Command fuel pump relay on with a scan tool. Observe fuel pressure gauge with fuel pump commanded on. Is fuel pressure within 55-62 psi (379-427 kPa)? If yes, go to next step. If no, go to step 10 .
  4. Monitor fuel pressure gauge for one minute. Does fuel pressure decrease by more than 5 psi (34 kPa)? If yes, go to step 8 . If no, 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 22 . If no, go to next step.
  6. Turn ignition on, with engine off. Monitor fuel pressure gauge. Start engine. Does fuel pressure decrease by 3-10 psi (21-69 kPa) when engine is started? If yes, go to next step. If no, go to step 21 .
  7. Operate vehicle within conditions to reproduce original symptoms. Monitor O2 and fuel trim parameters with a scan tool. Do any of scan tool parameters indicate a lean condition? If yes, go to step 15 . If no, problem is intermittent. See «INTERMITTENTS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-trouble-shooting-no-codes-43l__intermittents) in TROUBLE SHOOTING - NO CODES - 4.3L CHEVY EXPRESS & SAVANA article.
  8. Turn ignition off. Relieve fuel pressure. Raise and support vehicle. Disconnect fuel feed pipe from fuel filter outlet. Disconnect rear fuel return pipe from chassis fuel pipe. Drain any remaining fuel into an approved gasoline container. Install Fuel Line Shut-Off Adapters (J-37287) between rear fuel pipes and chassis fuel pipes. Open valves on fuel pipe shut-off adapters. Turn ignition on, with engine off. Command fuel pump relay ON with a scan tool. Bleed air from fuel pressure gauge. Command fuel pump relay ON and OFF with a scan tool. Close fuel feed pipe shut-off valve. Monitor fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step 17 . If no, go to next step.
  9. Turn ignition off. Open fuel feed pipe shut-off valve. Turn ignition on, with engine off. Command fuel pump relay on and off with a scan tool. Close fuel return pipe shut-off valve. Monitor fuel pressure gauge for one minute. Does fuel pressure remain constant? If yes, go to step 21 . If no, go to step 18 .
  10. Is fuel pressure more than 62 psi (427 kPa)? If yes, go to step 12 . If no, go to next step.
  11. Is fuel pressure more than zero psi? If yes, go to step 14 . If no, go to step 15 .
  12. Turn ignition off. Relieve fuel pressure. Disconnect fuel return hose from fuel rail return pipe. Attach a length of flexible hose to fuel rail return pipe. Place open end of flexible fuel hose into an approved gasoline container. Turn ignition on, with engine off. Monitor fuel pressure gauge while fuel pump is operating. Is fuel pressure within 55-62 psi (379-427 kPa)? If yes, go to step 20 . If no, go to next step.
  13. Inspect fuel rail outlet passage and fuel rail return pipe for a restriction. Did you find and correct condition? If yes, go to step 23 . If no, go to step 21 .
  14. Turn ignition off. Relieve fuel pressure. Disconnect fuel return hose from fuel rail return pipe. Install Fuel Line Shut-Off Adapter (J-37287) between fuel return pipe and fuel rail. Open valve in fuel pipe shut-off adapter. Turn ignition on, with engine off. Bleed air from 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 relay on with a scan tool. Slowly close valve in fuel return pipe shut-off adapter, while fuel pump is operating. Does fuel pressure increase to more than 62 psi (427 kPa)? If yes, go to step 21 . If no, go to next step.
  15. Inspect for restricted fuel filter or fuel feed pipe. Did you find and correct condition? If yes, go to step 23 . If no, go to next step.
  16. Inspect harness connectors and ground circuits of fuel pump for poor connections. Did you find and correct condition? If yes, go to step 23 . If no, go to next step.
  17. 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 and fuel tank for contaminants. Did you find and correct condition? If yes, go to step 23 . If no, go to step 22 .
  18. Open fuel return pipe shut-off valve. Remove upper intake manifold. Install engine compartment fuel feed and fuel return pipes to fuel meter body. Turn ignition on, with engine off. Inspect for a fuel leak from fuel pressure regulator. Is fuel pressure regulator leaking fuel? If yes, go to step 21 . If no, go to next step.
  19. Remove fuel injectors from intake manifold in order to isolate leaking fuel injector. After replacing injector(s), go to step 23 .
  20. Repair restricted fuel return pipe. After repairs, go to step 23 .
  21. Replace fuel pressure regulator. After replacing fuel pressure regulator, go to step 23 .
  22. Replace fuel sender. After replacing fuel sender, go to next step.
  23. Operate system in order to verify repair. Did you correct condition? If yes, system is okay. If no, go to step 3 .

IGNITION SYSTEMS

Note. For additional ignition system and component diagnosis, see IGNITION SYSTEMS in SYSTEM & COMPONENT TESTING - 4.3L CHEVY EXPRESS & SAVANA article.

CAMSHAFT POSITION SENSOR

For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.

CRANKSHAFT POSITION SENSOR

For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article.

Scheme 1

Scheme 1: DISTRIBUTOR IGNITION SYSTEM
Scheme 1: DISTRIBUTOR IGNITION SYSTEM

Scheme 2

Scheme 2
Scheme 2

Circuit Description

This system includes Crankshaft Position (CKP) sensor, Camshaft Position (CMP) sensor, ignition coil with Ignition Control (IC) module, secondary wires, spark plugs, and circuit conductors and connectors.

PCM controls ignition system and PCM monitors input signals from various engine sensors. The PCM controls dwell of ignition primary coil, computes desired spark timing and firing of ignition system via an IC timing control circuit to ignition control module.

Diagnostic Aids

Engine mechanical conditions may prevent distributor from rotating. Inspect following if distributor rotor does not rotate: A broken distributor drive shaft, worn or broken distributor drive gear, or worn/broken camshaft timing chain and gears. An intermittent may be caused by a poor connection, rubbed-through wire insulation or a wire broken inside insulation.

Test Description

The number below refers to step number on diagnostic procedure.

  1. 3 - This step is testing for a CKP sensor signal to PCM.
  2. 4 - This step is testing for an internally shorted camshaft position sensor.
  3. 9 - This step is testing for spark output at more than one spark plug wire. The Spark Tester (J-26792) requires a minimum of 25,000 volts to operate.
  4. 10 - This step determines if spark is being delivered to distributor cap.
  5. 20 - This test is testing if PCM is providing a timing control signal to ignition control module.
  6. 21 - This test checks for a basic engine mechanical problem.
  1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. After performing diagnostic system check, go to next step.
  2. Test fuse which supplies ignition 1 voltage to ignition coil assembly and Ignition Control Module (ICM). (Scheme 2) Is fuse open? If yes, go to step 32. If no, go to next step.
  3. Observe engine speed parameter with a scan tool. Crank engine. Is engine speed parameter more than 125 RPM? If yes, go to step 9. If no, go to next step.
  4. Turn ignition off. Disconnect CMP sensor electrical connector. CMP sensor is located inside distributor. Attempt to start engine. Does engine start and continue to run? If yes, go to step 26. If no, go to next step.
  5. Turn ignition on, with engine off. Measure voltage of 12-volt reference circuit of CMP sensor to a good ground with a DVOM. (Scheme 2) Is battery voltage present? If yes, go to next step. If no, go to step 8.
  6. Turn ignition off. Disconnect CKP sensor electrical connector. CKP sensor is located behind harmonic balancer. Turn ignition on, with engine off. Measure voltage from 12-volt reference circuit of CKP sensor to a good ground with a DVOM. (Scheme 2) Is battery voltage present? If yes, go to step 27. If no, go to next step.
  7. Turn ignition off. Test CKP 12-volt reference circuit for an open or short to ground. Did you find and correct condition? If yes, go to step 50. If no, go to next step.
  8. Turn ignition off. Test CMP 12-volt reference circuit for an open or a short to ground. Did you find and correct condition? If yes, go to step 50. If no, go to step 30.
  9. Turn ignition off. Disconnect a spark plug wire from a spark plug. Install Spark Tester (J-26792) into spark plug wire end. A few sparks then nothing is considered no spark. Observe spark tester. Crank engine. If there is no spark on one wire, test a second wire. Does multiple spark events occur on both spark plug wires? If yes, go to step 31. If no, go to next step.
  10. Disconnect ignition coil wire from distributor cap. Install spark tester into ignition coil wire end. Observe spark tester. Crank engine. Does multiple spark events occur? If yes, go to step 21. If no, go to next step.
  11. Disconnect ignition coil wire from ignition coil. Measure ignition coil wire resistance. Is resistance less than 1000 ohms per foot? If yes, go to next step. If no, go to step 44.
  12. Turn ignition off. Disconnect ignition coil electrical connector. Probe ignition coil control circuit of ignition coil with a test light that is connected to battery voltage. Crank engine. Does test light flash while cranking engine? If yes, go to step 15. If no, go to next step.
  13. Turn ignition off. Probe ignition coil control circuit of ignition coil with a test light connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step 16.
  14. Turn ignition off. Disconnect ignition control module electrical connector. Probe ignition coil control circuit of ignition coil with a test light connected to battery voltage. Does test light illuminate? If yes, go to step 40. If no, go to step 47.
  15. Turn ignition on, with engine off. Measure voltage from ignition 1 voltage circuit of ignition coil to a good ground with a DVOM. Is voltage more than 10 volts? If yes, go to step 29. If no, go to step 33.
  16. Turn ignition off. Disconnect ignition control module electrical connector. Turn ignition on, with engine off. Probe ignition coil control circuit of ignition control module with a test light that is connected to a good ground. Does test light illuminate? If yes, go to step 39. If no, go to next step.
  17. Turn ignition off. Test ignition coil control circuit between ignition coil and ignition module for an open or a high resistance. Did you find and correct condition? If yes, go to step 50. If no, go to next step.
  18. Turn ignition on, with engine off. Measure voltage from ignition 1 voltage circuit of ignition control module to a good ground with a DVOM. Is voltage more 10 volts? If yes, go to next step. If no, go to step 34.
  19. Probe ground circuit of ignition control module with a test light that is connected to battery voltage. Does test light illuminate? If yes, go to next step. If no, go to step 35.
  20. Measure voltage from IC timing control circuit of ignition control module to a good ground with a DVOM. Observe voltage on DVOM. Crank engine. Is voltage within 1-4 volts? If yes, go to step 28. If no, go to step 23.
  21. Remove distributor cap. Inspect inside distributor cap for damage or contamination. Did you find a condition? If yes, go to step 46. If no, go to next step.
  22. Observe distributor rotor. Crank engine. Does distributor rotor rotate when engine cranks? If yes, go to step 45. If no, see «DIAGNOSTIC AIDS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-basic-diagnostic-procedures__diagnostic-aids).
  23. Turn ignition off. Disconnect PCM electrical connectors. PCM is located on left front of engine compartment. Test IC timing control circuit for an open or a high resistance. Did you find and correct condition? If yes, go to step 50. If no, go to next step.
  24. Probe IC timing control circuit of PCM with a test light connected to battery voltage. Does test light illuminate? If yes, go to step 37. If no, go to next step.
  25. Turn ignition on, with engine off. Probe IC timing control circuit of PCM with a test light connected to a good ground. Does test light illuminate? If yes, go to step 38. If no, go to step 30.
  26. Test for an intermittent and for a poor connection at CMP sensor. Did you find and correct condition? If yes, go to step 50. If no, go to step 41.
  27. Test for an intermittent and for a poor connection at CKP sensor. Did you find and correct condition? If yes, go to step 50. If no, go to step 42.
  28. Test for an intermittent and for a poor connection at ignition control module. Did you find and correct condition? If yes, go to step 50. If no, go to step 47.
  29. Test for an intermittent and for a poor connection at ignition coil. Did you find and correct condition? If yes, go to step 50. If no, go to step 43.
  30. Test for an intermittent and for a poor connection at PCM. Did you find and correct condition? If yes, go to step 50. If no, go to step 48.
  31. Inspect spark plugs for damage or contamination. Did you find and correct condition? If yes, go to step 50. If no, problem is intermittent.
  32. Repair short to ground in ignition 1 voltage circuit. After repairs, go to step 49.
  33. Repair open or high resistance in ignition 1 voltage circuit between underhood fuse/relay block and ignition coil. After repairs, go to step 50.
  34. Repair open or high resistance in ignition 1 voltage circuit between underhood fuse/relay block and ignition control module. After repairs, go to step 50.
  35. Repair open or high resistance in ground circuit of ignition control module. After repairs, go to step 50.
  36. Repair open or high resistance in IC timing control circuit. After repairs, go to step 50.
  37. Repair short to ground in IC timing control circuit. After repairs, go to step 50.
  38. Repair short to voltage in IC timing control circuit. After repairs, go to step 50.
  39. voltage in ignition coil control circuit. After repairs, go to step 50.
  40. Repair short to ground in ignition coil control circuit. After repairs, go to step 50.
  41. Replace CMP sensor. After replacing sensor, go to step 50.
  42. Replace CKP sensor. After replacing sensor, go to step 50.
  43. Replace ignition coil. After replacing ignition coil, go to step 50.
  44. Replace ignition coil wire. After replacing coil wire, go to step 50.
  45. Replace distributor rotor. After replacing rotor, go to step 50.
  46. Replace distributor cap. After replacing distributor cap, go to step 50.
  47. Replace ignition control module. After replacing ignition control module, go to step 50.
  48. Replace PCM. See appropriate «REMOVAL & INSTALLATION - CHEVY EXPRESS & SAVANA - GASOLINE»(/chevrolet/chevy-express-h2500/2003-2003/remont/removal-installation/#engine-controls-removal-installation-gasoline) article. After replacing PCM, go to step 50.
  49. Replace fuse. After replacing fuse, go to next step.
  50. Clear DTCs with a scan tool. Turn ignition off for 30 seconds. Start engine. Let engine reach operating temperature. Are re any DTCs that have not been diagnosed? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(/chevrolet/chevy-express-h2500/2003-2003/remont/testing-diagnostics/#engine-controls-self-diagnostics-43l__diagnostic-trouble-code-definitions) in SELF-DIAGNOSTICS - 4.3L CHEVY EXPRESS & SAVANA article. If no DTC(s) are set, system is okay.

IDLE SPEED & IGNITION TIMING

Idle speed and ignition timing are controlled by PCM. Incorrect idle speed are normally caused by dirty throttle plate or vacuum leaks. Ensure all vacuum components are functioning properly.

CHEVY EXPRESS - G1500

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

CHEVY EXPRESS - G2500

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

SAVANA - G1500

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

SAVANA - G2500

See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

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