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HOMESERVICE MANUALSOLDSMOBILE2004BRAVADA RWDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 52 (ENGINE CONTROL SYSTEM - SELF-DIAGNOSTICS - 4.2L)DIAGNOSTIC TESTSDTC P1639: 5-VOLT REFERENCE B CIRCUITDIAGNOSTIC PROCEDURES
2004 Oldsmobile Bravada RWD

Diagnostic Procedures

2004 Oldsmobile Bravada RWDSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. 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. NOTE: If the vehicle has a cranks but will not run condition proceed to next step.
  2. Observe the Freeze Frame/Failure Records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC or as close as possible to the Freeze Frame/Failure Records data that you observed. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  3. Turn OFF the ignition. Disconnect the throttle body electrical connector. Turn ON the ignition, with the engine OFF. Measure the voltage from the 5-volt reference B circuit of the Throttle Position (TP) sensor 2 to a good ground with a Digital Multimeter (DMM). Is the voltage near 5 V? If yes, go to step  5 . If no, go to next step.
  4. Is the voltage more than 5 V? If yes, go to step  8 . If no, go to step  6 .
  5. Connect the throttle body electrical connector. Disconnect the manifold absolute pressure (MAP) sensor. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground with a DMM. Is the voltage near 5 V? If yes, see INTERMITTENT CONDITIONS  . If no, go to step  9 .
  6. Monitor the DMM while disconnecting all other devices connected to the 5-volt reference B circuit one at a time. If voltage changes when one of the above components are disconnected, replace the component. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Was a component replaced? If yes, go to step  12 . If no, go to next step.
  7. Turn OFF the ignition. Disconnect the PCM. Test the 5-volt reference B circuit for a short to ground or for any sensor low reference circuit. If a condition is found, repair as necessary. Did you find and correct a condition? If yes, go to step  12 . If no, go to step  10 .
  8. Turn ON the ignition, with the engine OFF. Test the following circuits for a short to voltage:
    • The 5-volt reference B circuit.
    • The MAP sensor signal circuit.

    If a condition is found, repair as necessary. Did you find and correct a condition? If yes, go to step  12 . If no, go to step  10 .

  9. Replace the throttle body assembly. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  12 .
  10. Test the 5-volt reference B circuit for a short to the TAC motor control 1 or 2 circuits. Did you find and correct a condition? If yes, go to step  12 . If no, go to next step.
  11. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  12. 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 .
  13. 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.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.