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Engine Controls - System & Component Testing - 6.0L W/bifuel & Cng: Diagnosis Chevrolet Silverado 1500 HD

Testing & Diagnostics ~2119 words

Circuit Description

The PCM controls the fuel system while the vehicle is operating on CNG. A High Pressure Lock-Off (HPL) solenoid in each CNG tank and a Low Pressure Lock-Off (LPL) solenoid in fuel rail prevent fuel flow. The PCM commands ONLY the HPL's open for one second at every ignition on for a CNG prime pulse. The CNG prime pulse is performed in order to charge the fuel line and also allows the Fuel Tank Pressure (FTP) sensor to monitor the amount of fuel pressure in the tanks. The PCM commands both the HPL and LPL open when engine RPM indicates the engine is cranking or running on CNG.

The Alternative Fuel (AF) lock-off relay's coil and switch are supplied power whenever the ignition is in the Start or Run position. The PCM controls the ground path. When the AF lock-off relay is energized, power is supplied to the HPL and LPL solenoids.

Diagnostic Procedures

  1. Perform diagnostic system check. See «DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS»(ref-159156-S07074324102003111300000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L CHEVY EXPRESS & SAVANA - BI-FUEL & CNG or «DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS»(ref-159297-S00366181602003112400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L SILVERADO & SIERRA - BI-FUEL & CNG article. After performing diagnostic system check, go to next step.
  2. Is DTC P0005 or P2665 set? If yes, diagnose affected DTC(s). See «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-159156-S06111585432003111300000) in SELF-DIAGNOSTICS - 6.0L CHEVY EXPRESS & SAVANA - BI-FUEL & CNG article or «DIAGNOSTIC TROUBLE CODE DEFINITIONS»(ref-159297-S15239216512003112400000) in SELF-DIAGNOSTICS - 6.0L SIERRA & SILVERADO - BI-FUEL & CNG article. If no, go to next step.
  3. Turn ignition on, with engine off. Command the HPL on and off with a scan tool. Listen for operation of the HPLs. HPL is threaded into CNG tank. Do the HPLs respond to the scan tool commands? If yes, go to next step. If no, go to step 5.
  4. Command the LPL solenoid on and off with a scan tool. Listen for operation of the LPL. LPL is located on left engine valve cover. Does the LPL respond to the scan tool commands? If yes, go to step 18. If no, go to step 6.
  5. Command the HPL solenoids on and off with a scan tool. Listen or feel for operation of the AF lock-off relay. AF lock-off relay is located on rear center of engine compartment. Does the relay respond to the scan tool commands? If yes, go to step 14. If no, go to step 15.
  6. Command the LPL solenoid on and off with a scan tool. Listen or feel for operation of the AF lock-off relay. AF lock-off relay is attached to left side of underhood fuse/relay block. Does the relay respond to the scan tool commands? If yes, go to step 8. If no, go to next step.
  7. Disconnect AF lock-off relay harness connector. Probe AF lock-off relay switch ignition circuit terminal No. 30 (Orange wire) with a test light connected to ground. (Схема №17) Turn ignition on, with engine off. Is test light illuminated? If yes, go to step 10. If no, go to step 11.
  8. Disconnect the LPL solenoid. Probe the LPL solenoid ground circuit terminal "B" (Red wire) with a test light connected to battery voltage. (Схема №17) Is test light illuminated? If yes, go to next step. If no, go to step 13.
  9. Probe the LPL solenoid ignition voltage circuit terminal "A" (Gray wire) with a test light connected to ground. Command the LPL solenoid on and off with a scan tool. Does the test light respond to the scan tool commands? If yes, go to step 17. If no, go to step 12.
  10. Test for an intermittent and for a poor connection at the AF lock-off relay. Did you find and correct the condition? If yes, go to step 18. If no, go to step 16.
  11. Repair open in AF lock-off relay switch power circuit. (Схема №17) After repairs, go to step 18.
  12. Repair LPL solenoid power circuit between relay and solenoid for open. After repairs, go to step 18.
  13. Repair open in LPL solenoid ground circuit. After repairs, go to step 18.
  14. Repair open in HPL solenoid's ground circuit. After repairs, go to step 18.
  15. Replace AF lock-off relay. After replacing relay, go to step 18.
  16. Replace AF lock-off relay. After replacing relay, go to 18.
  17. Replace LPL solenoid. After replacing solenoid, go to next step.
  18. Clear DTC information from PCM using scan tool. Turn ignition off and wait 30 seconds. Start and operate engine at idle. Observe the MIL. Observe vehicle performance and driveability. Does the vehicle operate on CNG with normal driveability and no MIL illumination? If yes, system is okay. If no, see «DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS»(ref-159156-S07074324102003111300000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L CHEVY EXPRESS & SAVANA - BI-FUEL & CNG or «DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS»(ref-159297-S00366181602003112400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L SILVERADO & SIERRA - BI-FUEL & CNG article.

FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL

Note. For component locations, see COMPONENT LOCATIONS . For circuit reference, see WIRING DIAGRAMS .

The Fuel Injector Tester (J-39021) energizes the CNG fuel injector for a precise amount of time allowing a measured amount of fuel into the manifold. This causes a drop in system fuel pressure that can be recorded and used to compare each fuel injector.

  1. Perform Diagnostic System Check Alternative Fuels - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS»(ref-159156-S07074324102003111300000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L CHEVY EXPRESS & SAVANA - BI-FUEL & CNG or «DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS»(ref-159297-S00366181602003112400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L SILVERADO & SIERRA - BI-FUEL & CNG article. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Perform «FUEL INJECTOR COIL TEST»(ref-153237-S26473674432003032600000) . After performing Fuel Injector Coil Test, go to next step.
  3. Start and operate engine at idle. Observe the fuel rail pressure sensor parameter with a scan tool. Is the fuel pressure within 160-170 psi (1103-1172 kPa)? If yes, go to next step. If no, diagnose fuel system. Refer to «FUEL SYSTEM DIAGNOSIS»(ref-152801-S36073921212003022600000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL/CNG article.
  4. Turn ignition off. Turn ignition on, with engine off. Monitor the fuel rail pressure sensor parameter with a scan tool. Does the fuel rail pressure remain constant? If yes, go to next step. If no, diagnose fuel system. Refer to «FUEL SYSTEM DIAGNOSIS»(ref-152801-S36073921212003022600000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL/CNG article.
  5. Turn ignition off. Connect the Fuel Injector Tester (J-39021) to a fuel injector. Set the amperage supply selector switch on the fuel injector tester to the Balance Test 0.5-2.5 amp position. Turn ignition on, with engine off. Record fuel pressure indicated by the fuel rail pressure sensor after fuel pressure stabilizes. This is the first pressure reading. Record fuel pressure value immediately after the CNG fuel injector stops pulsing. The fuel pressure may rise after fuel injector stops pulsing. DO NOT record the higher fuel pressure value. Energize the CNG fuel injector by depressing the Push to Start Test button on the fuel injector tester. Record fuel pressure indicated by the fuel rail pressure sensor. This is the second fuel pressure reading. Repeat procedure for each fuel injector. Subtract the second pressure reading from the first pressure reading for one fuel injector. The result is the pressure drop value. Obtain a pressure drop value for each fuel injector. Add all of the individual pressure drop values. This is the total pressure drop. Divide the total pressure drop by the number of fuel injectors. This is the average pressure drop. Does any fuel injector have a pressure drop value that is more than the average pressure drop or less than the average pressure drop by 2.0 psi (14 kPa)? If yes, go to next step. If no, refer to «FUEL SYSTEM DIAGNOSIS»(ref-152801-S36073921212003022600000) under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL/CNG article.
  6. Replace the affected CNG fuel injector. After replacing injector(s), go to next step.
  7. Operate system in order to verify repair. Did you correct the condition? If yes, system is okay. If no, go to «SYMPTOMS»(ref-152996-S17492894172003031000000) in TROUBLE SHOOTING - NO CODES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article.

FUEL INJECTOR CIRCUIT DIAGNOSIS

A malfunction in the fuel injection circuit can set a DTC. For testing procedures and specifications, perform appropriate diagnostic test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 6.0L CHEVY EXPRESS & SAVANA - BI-FUEL & CNG article or DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-DIAGNOSTICS - 6.0L SIERRA & SILVERADO - BI-FUEL & CNG article.

FUEL INJECTOR COIL TEST

Note. For component locations, see COMPONENT LOCATIONS . For circuit reference, see WIRING DIAGRAMS .

The PCM enables the appropriate CNG fuel injector on the intake stroke for each cylinder. The PCM is not capable of operating the high current CNG fuel injectors. The PCM injector pulse width signals are received by the Fuel Injector Control Module (FICM) and duplicate pulse width signals are generated by the FICM in order to operate the CNG injectors. The FICM controls each fuel injector by grounding the control circuit via a solid state device called a driver. A fuel injector coil winding resistance that is too high or low, will affect engine driveability. A fuel injector control circuit DTC may not set, but a misfire may be apparent. The fuel injector coil windings are affected by temperature. The resistance of the fuel injector coil windings will increase as the temperature of the fuel injector increases.

Diagnostic Aids

  1. Operating vehicle over a wide temperature range may help isolate the fuel injector that is causing the condition.
  2. Perform fuel injector coil test within the conditions of the customer's concern. A fuel injector condition may only be apparent at a certain temperature or under certain conditions.
  3. If fuel injector coil test does not isolate the condition, perform fuel injector balance test. Refer to «FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL»(ref-153237-S01028591802003032600000) .
  1. Perform Diagnostic System Check Alternative Fuels - Engine Controls. See «DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS»(ref-159156-S07074324102003111300000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L CHEVY EXPRESS & SAVANA - BI-FUEL & CNG article or «DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS»(ref-159297-S00366181602003112400000) under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L SILVERADO & SIERRA - BI-FUEL & CNG article. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Observe Engine Coolant Temperature (ECT) parameter with scan tool. Is ECT value within 50-90°F (10-32°C)? If yes, go to next step. If no, go to step 4 .
  3. Disconnect CNG fuel injectors multi-way harness connector. Using a DVOM, measure resistance of each CNG fuel injector. Do any of the fuel injectors display a resistance outside the specified range of 1-2 ohms? If yes, go to step 6 . If no, see «DIAGNOSTIC AIDS»(ref-153237-S20745660582003032600000) .
  4. Measure resistance of each CNG fuel injector with a DVOM. Record each fuel injector value. Subtract the lowest resistance value from the highest resistance value. Is the difference equal to or less than 0.5 ohm? If yes, go to «DIAGNOSTIC AIDS»(ref-153237-S20745660582003032600000) . If no, go to next step.
  5. Add all of the CNG fuel injector resistance values to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors to obtain an average resistance value. Subtract the lowest and the highest individual fuel injector resistance values from the average resistance value. Replace CNG fuel injector that displays the greatest resistance difference, above or below the average. After replacing injector(s), go to step 7 .
  6. Replace fuel injector(s) that are out of the specified range. After replacing injector(s), go to next step.
  7. Operate the system in order to verify the repair. Did you correct the condition? If yes, system is okay. If no, go to step 2 .

FUEL SYSTEM PRESSURE TEST

Note. For fuel system pressure testing, see FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL/CNG article.

ELECTRONIC IGNITION SYSTEM DIAGNOSIS

See ELECTRONIC IGNITION SYSTEM under IGNITION SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL/CNG article.

EVAP Control System Diagnosis

For EVAP control system diagnosis, perform the following. On Chevy Express and Savana, see appropriate INSPECTION/MAINTENANCE PROCEDURES under DRIVE CYCLES in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L EXPRESS & SAVANA - GASOLINE article. On Sierra & Silverado, see appropriate INSPECTION/MAINTENANCE PROCEDURES under DRIVE CYCLES in SELF-DIAGNOSTICS - 4.8L, 5.3L & 6.0L "C", "K" & "N" SERIES - GASOLINE article.

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