DTC P1639 - 5 Volt Reference B Circuit
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, 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 19 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
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, 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 malfunction. |
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 (OBD) System Check performed? | -- | ||
2 | Visually/physically check the PCM and engine grounds. Refer to Ground Distribution in Electrical Diagnosis. Was a problem found? | -- | ||
3 |
Does the scan tool display voltage greater than the first specified value or less than the second specified value? | 4.8 0.1 V | Go to DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit | |
4 |
| 5.5 V | ||
5 |
Is voltage greater than the specified value indicated? | 5.5 V | ||
6 | Locate and repair short to voltage in the 5 volt reference B circuit. Refer to Repair Procedures in Electrical Diagnosis. Is action complete? | -- | -- | |
7 | Is voltage less than the specified value indicated? | 4.5V | ||
8 |
Was a problem found? | -- | ||
9 |
Was a problem found? | -- | ||
Replace PCM. Important:: The replacement PCM must be programmed. Go to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||
11 |
Note test result; does the scan tool indicate DTC P1639 failed this ign? | -- | System OK |
