P1639

CIRCUIT DESCRIPTION
The powertrain control module (PCM) uses the 5-volt reference 2 circuit as a sensor feed for the fuel tank pressure (FTP) sensor. The PCM monitors the voltage on the 5-volt reference 2 circuit. If the voltage is out of tolerance, the PCM will set the diagnostic trouble code (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 1-5:

Steps 6-13:

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