LEMON Manuals: Even more car manuals for everyone
Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 81 (Engine Controls - Self-Diagnostics - 8.1L) >> Diagnostic Tests >> DTC P1639: 5-Volt Reference 2 Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page does not describe the selected car, but rather 13 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 GMC Savana Special, 2002 GMC Savana Camper Special, and 2002 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Install a scan tool. Start the engine. Idle the engine for 2 minutes. Monitor the DTCs using a scan tool. Did both DTCs P1635 and P1639 fail this ignition cycle? If yes, see DTC P1635: 5-VOLT REFERENCE 1 CIRCUIT . If no, go to next step.
  3. Did DTC P1639 fail this ignition cycle? If yes, go to step  5. If no, go to next step.
  4. Turn ON the ignition, with the engine OFF. Review the Freeze Frame/Failure Records data for this DTC and observe the parameters. Turn OFF the ignition for 15 seconds. Start the engine. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame/Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in the Conditions for Running DTC. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number using the scan tool. Does the scan tool indicate the DTC set this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  5. Turn OFF the ignition. Disconnect the PCM connector C1. Connect the test lamp to battery voltage. Probe the PCM connector 5-volt reference circuits for the following components:
    • The TP sensor.
    • The FTP sensor.

    Does the test lamp illuminate for any of the circuits? If yes, go to step  7. If no, go to next step.

  6. Test resistance from each 5-volt reference circuit to all other PCM circuits at the PCM harness connector using the Digital Multimeter (DMM). Example: probe one lead to the TP sensor 5-volt reference at the PCM harness connector circuit and probe the other lead to each terminal at the PCM harness connector. This must be performed for each 5-volt reference circuit. Do any of the circuits indicate a resistance of 0-2 ohms? If yes, go to step  8. If no, go to step  9.
  7. Repair the short to ground on the appropriate 5-volt reference circuit. After repairs, go to step  10.
  8. Repair the short between the appropriate 5-volt reference circuit and the PCM circuit that had continuity. After repairs, go to step  10.
  9. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  10. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  11. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
scientia non olet · About LEMON Manuals