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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 107 (Engine Controls - Self-Diagnostics - 3.5L) >> Diagnostic Tests >> DTC P1639: 5-Volt Reference "B" Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Intrigue and 2002 Oldsmobile Aurora. 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, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Check PCM and engine grounds. Ensure grounds are clean and tight. See WIRING DIAGRAMS article. If any problems are found, repair as necessary. After repairs, go to step  11. If no problems are found, go to next step.
  3. If any other DTCs are set, repair DTCs as necessary before continuing with this test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are set, go to next step.
  4. Turn ignition off. Disconnect the A/C refrigerant pressure sensor and fuel tank pressure sensor. Turn ignition on. Using a Digital Multimeter (DMM), measure voltage on the 5-volt reference circuit at any one of the disconnected harness connectors. Is voltage within 4.5-5.5 volts? If yes, go to next step. If no, go to step  8.
  5. Reconnect one disconnected sensor at a time while measuring voltage between ground and 5-volt reference circuit at other disconnected sensor harness connector. If sensor being reconnected caused voltage to vary outside 4.5-5.5 volts, go to next step. If sensor being reconnected did not cause voltage to vary outside 4.5-5.5 volts, see DIAGNOSTIC AIDS .
  6. Check for short to power or short to ground on all other circuits connected to affected sensor. See WIRING DIAGRAMS article. If a problem is found and corrected, reconnect the component and recheck the effect on the 5-volt reference circuit as in the previous step. Was a problem found and corrected? If yes, go to step  11. If no, go to next step.
  7. Replace affected sensor. After repairs, go to step  11.
  8. Turn ignition off. Disconnect PCM harness connector. Turn ignition on. Check 5-reference circuit for short to ground and short to power. Was a problem found? If yes, go to next step. If no, go to step  11. If wiring is okay, go to next step.
  9. Repair the 5-volt reference circuit as necessary. After repairs, go to step  11.
  10. Replace PCM. Program replacement PCM. See PROGRAMMING . After repairs, go to next step.
  11. Turn ignition off. Reconnect all disconnected connectors. Turn ignition on. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within conditions for setting the DTC. See CONDITIONS FOR SETTING DTC . If DTC runs and passes, go to next step. If DTC resets, go to step  2.
  12. Using scan tool, check for any other DTCs that are set. If no other DTCs are set, system is okay. If any other DTCs are set, repair DTCs as necessary. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
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