Refer to
ECT, MAP, TP, IAT, and A/C Systems
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 will not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data. |
Conditions for Clearing the MIL/DTC
| • | A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool Clear Info function. |
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? | -- | Go to the Powertrain On-Board Diagnostic System Check | |
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 | |
4 |
Is voltage greater than the specified value indicated? | 5.5V | ||
5 | Monitor DVM 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? | 5.5V | ||
6 |
Was a problem found? | -- | ||
7 | Locate and repair short to voltage in A/C refrigerant pressure sensor signal circuit wiring (refer to Engine Electrical). Is action complete? | -- | -- | |
8 | Is voltage less than the specified value indicated? | 4.5V | ||
9 |
Was a problem found? | -- | ||
Replace PCM. Important: Replacement PCM must be programmed Refer to PCM Replacement/Programming. Is action complete? | -- | -- | ||
11 |
Note test result does scan tool indicate DTC P1639 failed this ign? | -- | Repair complete |
