P1639

Diagnostic Chart:

Schematic:

CIRCUIT DESCRIPTION
The 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, DTC P1639 will set.

CONDITIONS FOR SETTING THE DTC
^ The PCM detects voltage out of tolerance on the 5 volt reference B circuit.
^ Above condition is present for more 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 and Failure Records data.
^ If the misfire is determined to be catalyst damaging, the PCM will flash the MIL.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM will turn OFF the MIL during the third consecutive trip in which the diagnostic has been 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.

DIAGNOSTIC AIDS

IMPORTANT: Inspect the PCM and engine grounds for being secure and clean.

Check for the following conditions:
^ Poor connection at the PCM - Inspect harness connectors for
- Backed out terminals
- Improper mating
- Broken locks
- Improperly formed or damaged terminals
- Poor terminal to wire connection
^ Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, turn ON the ignition, with the engine OFF and observe the A/C pressure display on the scan tool while moving connectors and wiring harnesses related to the A/C refrigerant pressure sensor. A change in the A/C pressure display will indicate the location of the malfunction.

If the DTC cannot be duplicated and is determined to be intermittent, reviewing the Failure Records can be useful in determining when the DTC was last set. Also refer to Testing for Intermittent and Poor Connections in Diagrams.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
11. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.