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Home >> Chevrolet >> 1997 >> Lumina Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 3.1L Engine >> Diagnostic Trouble Codes >> DTC P1639 - 5-Volt Reference "B" Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the BASIC TESTING - 3.1L article. Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. Go to next step.
  2. Ensure PCM and engine grounds are secure and clean. If a problem is found, go to step 11). If no problem is found, go to next step.
  3. Using scan tool, select DTC INFO, LAST TST FAIL. If DTC P0530 also set, go to DTC P0530 . If DTC is not set, go to next step.
  4. Turn ignition off. Disconnect PCM connectors. Turn ignition on. Using a DVOM, check voltage between PCM harness connector ground and 5-volt reference "B" circuits. If voltage is greater than 5.5 volts, go to next step. If voltage is not greater than 5.5 volts, go to step 8).
  5. Using DVOM, check voltage between PCM harness connector ground and 5-volt reference "B" circuits. Disconnect A/C refrigerant pressure sensor. If voltage is greater than 5.5 volts, go to next step. If voltage is not greater 5.5 volts, go to step 7).
  6. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Check 5-volt reference "B" circuit for short to voltage. If short to voltage is found, repair as necessary. After repairs, go to step 11). If no short to voltage is found, go to step 10).
  7. Locate and repair short to voltage in A/C refrigerant pressure sensor signal circuit. After repairs, go to step 11).
  8. If voltage is less than 4.5 volts, go to next step. If voltage is not less than 4.5 volts, go to step 10).
  9. Turn ignition off. Disconnect PCM harness connectors. Turn ignition on. Check 5-volt reference "B" circuit for short to ground. If short to ground is found, repair as necessary. After repairs, go to step 11). If no short to ground is found, go to next step.
  10. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  11. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P1639. If scan tool displays DTC P1639 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P1639 FAILED THIS IGN, repair is complete.
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