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Home >> Oldsmobile >> 1996 >> LSS 3.8 1 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control Systems Tests W/Codes >> Diagnostic Trouble Codes >> DTC P1639 - 5 Volt-Reference "B" Circuit >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. 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. Ensure A/C is off. Observe A/C high side pressure on scan tool. If pressure displays a voltage of greater than 4.8 volts or less than 0.1 volt, go to DTC P0530 for diagnosis of pressure sensor circuit. If voltage displayed is not greater than 4.8 volts or less than 0.1 volt, go to next step.
  4. Unplug A/C pressure sensor connector. Using DVOM, check voltage between sensor ground circuit and sensor 5-volt reference circuit. If voltage is greater than 5.5 volts, go to next step. If not, go to step 7).
  5. 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 more than 5.5 volts, go to next step. If voltage is 5.5 volts or less, go to step 10).
  6. Locate and repair short to voltage in A/C refrigerant pressure sensor signal circuit. Go to step 11).
  7. If voltage is less than 4.5 volts, go to next step. If voltage is 4.5 volts or more, go to step 9).
  8. Check for short to voltage in A/C pressure sensor signal circuit. Repair as necessary and go to step 11). If no repairs are required, go to step 10).
  9. Ignition off. Disconnect PCM connectors. Turn ignition on. Check 5-volt reference "B" circuit for short to ground. If short to ground is found, repair as necessary and go to step 11). If no short to ground is found, go to next step.
  10. Replace PCM. Program replacement PCM using required equipment. 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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