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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 244 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING - 6.0L W/BiFuel & CNG) >> Modules, Motors, Relays & Solenoids >> Alternative Fuel Lock-Off Relay >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 GMC Sierra, 2003 GMC Savana, 2003 Chevrolet Silverado, and 2003 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L CHEVY EXPRESS & SAVANA - BI-FUEL & CNG or DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS 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 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. 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. See Figure . 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. See Figure . 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. See Figure . 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 under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L CHEVY EXPRESS & SAVANA - BI-FUEL & CNG or DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS - 6.0L SILVERADO & SIERRA - BI-FUEL & CNG article.
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