P1639

CIRCUIT DESCRIPTION
The PCM uses the 5-volt reference 2 circuit as a sensor feed for the following sensors:
^ The AC pressure sensor
^ The fuel tank pressure (FTP) sensor

The PCM monitors the voltage on the 5-volt reference 2 circuit. If the voltage is outside an acceptable range 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 2 circuit.
^ Above condition is present for longer than 10 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed.
^ The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed.
^ The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
^ The DTC can be cleared by using a scan tool.

TEST DESCRIPTION

Steps 1-6:

Steps 7-18:

The number below refers to the step number on the diagnostic table.
9. The ignition must be turned OFF and the PCM powered down or the test may become inaccurate.