P1639

Schematic:

CIRCUIT DESCRIPTION
The PCM uses a common 5.0 volt reference circuit as a sensor feed to the Fuel Tank Pressure sensor and the A/C Refrigerant Pressure sensor.

The PCM monitors the voltage on the 5.0 volt reference circuit. This DTC sets if the voltage is out of range.

CONDITIONS FOR RUNNING THE DTC
The engine operating.

CONDITIONS FOR SETTING THE DTC
^ The 5.0 volt reference circuit is out of range.
^ The above condition is present for more than 2 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
^ The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The PCM turns the Malfunction Indicator Lamp (MIL) OFF after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
^ A last test failed (current DTC) clears when the diagnostic runs and does not fail.
^ A History DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.

DIAGNOSTIC AIDS

IMPORTANT:
^ Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.
^ For any test that requires probing the PCM or component harness connectors, use the J 35616-A connector test adapter kit. Using this kit prevents damage to the harness connector terminals. Refer to Using Connector Test Adapters in Diagrams.

A fuel level sensor signal circuit that is shorted to B+ may set this DTC.

If no circuit conditions can be found, test the affected component.

For an intermittent condition, refer to Symptoms. Symptom Related Diagnostic Procedures

TEST DESCRIPTION

Steps 1 - 4:

Steps 5 - 11:

Steps 12 - 15:

The numbers below refer to the step numbers on the diagnostic table.
2. The 5 volt reference circuits for the sensors are connected together inside the PCM. Both DTCs P1635 and P1639 set at the same time, indicates a 5 volt reference circuit is shorted to a voltage.
5. This step determines if a 5 volt reference circuit is shorted to ground.
6. This step tests for a signal circuit shorted to voltage.
7. The 5 volt reference circuits may be shorted to another PCM circuit. The shorted circuit may not be apparent when the PCM harness connector is disconnected. Testing continuity from each 5 volt reference circuit isolates the shorted circuit.
11. This step is testing for a component failure. Disconnecting each component individually isolates which component might be causing this DTC to set.