Refer to Engine Controls Schematics .
Circuit Description
The Powertrain Control Module (PCM) uses the 5 volt reference B circuit as a sensor feed to 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 ignition is ON.
Conditions for Setting the DTC
| • | The PCM detects a voltage out of tolerance condition on the 5 volt reference B circuit. |
| • | The above condition is present for more than 10 seconds. |
Action Taken When the DTC Sets
The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.
Conditions for Clearing the MIL/DTC
| • | The DTC becomes history when the conditions for setting the DTC are no longer present. |
| • | The history DTC clears after 40 malfunction free warm-up cycles. |
| • | The PCM receives a clear code command from the scan tool. |
Diagnostic Aids
Inspect for the following conditions:
| • | A faulty connection at the PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. |
| • | A damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the A/C pressure display on the scan tool while moving connectors and wiring harnesses related to the fuel tank pressure sensor. |
| • | Verify that the PCM and engine grounds are secure and clean. Refer to Power and Grounding Component Views in Wiring Systems. |
Refer to following procedures in Wiring Systems:
Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain OBD System Check? | -- | ||
2 | Visually and physically inspect the PCM and engine grounds. Ensure that the grounds are clean and secure. Was a problem found? | -- | ||
3 | Select DTC info, Last Test Fail and note if any other DTCs are set. Are there any EVAP codes set? | -- | Go to applicable DTC | |
4 |
Is the voltage more than the specified value? | 5.0 V | ||
5 | Monitor a DMM connected between the 5 volt reference B circuit and the PCM ground circuit while disconnecting A/C pressure sensor. Is voltage more than the specified value still indicated? | 5.0 V | ||
6 |
Did you find and correct the condition? | -- | ||
7 | Locate and repair short to voltage on the fuel tank or A/C pressure sensor signal circuit or ground circuit wiring. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
8 | Is the voltage less than the specified value? | 4.5 V | ||
9 |
Did you find and correct the condition? | -- | ||
|
Important: : The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Did you complete the replacement? | -- | -- | ||
11 |
Does the scan tool indicate DTC P1639 failed this ignition? | -- | System OK |
