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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 379 (Engine Controls Self-Diagnostics - 3.4L) >> Diagnostic Tests >> DTC P1635: 5-Volt Reference Low >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
  2. Observe the Freeze Frame/Failure Records for this DTC. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running. See CONDITIONS FOR RUNNING . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to next step. If no, problem is intermittent. Go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.
  3. Turn ignition switch to OFF position. Disconnect the EGR valve position sensor. Turn ignition switch to RUN position, engine OFF. Command the EGR solenoid to 100 percent using a scan tool. Measure the voltage from the 5-volt reference circuit to a good ground using a DMM. Is the voltage 4.8-5.2 volts? If yes, go to step  5. If no, go to next step.
  4. Is the voltage measured in the previous step more than 5.2 volts? If yes, go to step  8. If no, go to step  11.
  5. Connect the EGR valve. Disconnect the MAP sensor harness connector. Command the EGR solenoid to 100 percent using a scan tool. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground using a DMM. Is the voltage 4.8-5.2? If yes, see DIAGNOSTIC AIDS . If no, go to step  11.
  6. Monitor a DMM while disconnecting all other devices connected to the 5-volt reference circuit, one at a time. If voltage changes when one of the devices are disconnected, replace the component. Was a component replaced? If yes, go to step  13. If no, go to next step.
  7. Turn ignition switch to OFF position. Disconnect the PCM harness connectors. Check the 5-volt reference circuit for a short to ground or any sensor low reference circuit. Did you find and correct the condition? If yes, go to step  13. If no, go to step  12.
  8. Monitor the DMM while disconnecting the MAP sensor and FTP sensor, one at a time. If the voltage returns to 4.8-5.2 volts when one of the devices is disconnected, test that sensors signal circuit for a short to voltage. Did you find and correct the condition? If yes, go to step  13. If no, go to next step.
  9. Check the 5-volt reference circuits for a short to voltage. Did you find and correct the condition? If yes, go to step  13. If no, go to next step.
  10. Check for a short between the EGR 5-volt reference circuit and the EGR solenoid high control circuit. Did you find and correct the condition? If yes, go to step  13. If no, go to step  12.
  11. Replace the EGR valve. After repair, go to step  13.
  12. Replace PCM. See POWERTRAIN CONTROL MODULE in appropriate REMOVAL & INSTALLATION article. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  13. Using a scan tool, clear the DTCs. Turn ignition switch to OFF position. Start the engine. Operate the vehicle within the Conditions For Running. See CONDITIONS FOR RUNNING . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  14. Using the scan tool, observe the stored information in CAPTURE INFO. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay at this time.
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