P1639

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) uses the 5-volt reference B circuit as a sensor feed for the A/C refrigerant pressure sensor. The PCM monitors the voltage on the 5-volt reference B circuit. If the voltage is out of tolerance, the PCM will set DTC P1639.

CONDITIONS FOR RUNNING THE DTC
The engine must be running.

CONDITIONS FOR SETTING THE DTC
^ The PCM detects a voltage out of tolerance condition on the 5-volt reference B circuit.
^ Above condition is present for longer than 10 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ First failure:
- The MIL is not turned ON.
- A DTC is stored in memory under Failed Last Test.
- The Failure Records are stored.
^ Second consecutive drive cycle with a failure:
- The MIL is turned ON.
- A DTC is stored in memory under history.
- The Freeze Frame data is stored.
- The Failure Records are stored.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The control module turns OFF the Malfunction Indicator Lamp (MIL) after the third consecutive trip the diagnostic has run and passed.
^ The history DTC will clear if the fault conditions have not been detected for 40 warm-up cycles.
^ A scan tool can be used to clear DTC information.

TEST DESCRIPTION

Steps 1-6:

Steps 7-13:

The numbers below refer to the step numbers on the diagnostic table.
7. The ignition must be turned OFF and the PCM powered down or the test may become inaccurate.