Circuit Description
The 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 Setting the DTC
| • | The PCM detects a voltage out of tolerance condition on the 5 Volt Reference B circuit. |
| • | Above condition for longer 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
Check for the following conditions:
| • | Poor connection at PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | 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 A/C refrigerant pressure sensor. A change in the A/C pressure display will indicate the location of the fault. |
| • | Inspect PCM and engine grounds for being secure and clean. |
Reviewing the Fail 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
Number(s) below refer to the step number(s) on the Diagnostic Table:
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain ON Board Diagnostic System Check performed? | -- | ||
2 | Visually/physically check 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 any other DTCs set. Is DTC P0530 also set? | -- | Go to DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit | |
4 |
Is voltage greater than the specified value indicated? | 5.0V | ||
5 | Monitor DMM connected between the 5 volt reference B circuit and the PCM ground circuit while disconnecting the A/C refrigerant pressure sensor. Is voltage greater than the specified value still indicated with the A/C refrigerant pressure sensor disconnected? | 5.0V | ||
6 |
Was a problem found? | -- | ||
7 | Locate and repair short to voltage in A/C refrigerant pressure sensor signal circuit wiring. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
8 | Is voltage less than the specified value indicated? | 4.5V | ||
9 |
Was a problem found? | -- | ||
|
Important: The replacement PCM must be programmed Refer to Powertrain Control Module Replacement/Programming . Replace PCM. Is the action complete? | -- | -- | ||
11 |
Note test result does scan tool indicate DTC P1639 failed this ignition? | -- | System OK |
