The PCM uses the 5 Volt Reference B circuit as a sensor feed for the A/C refrigerant pressure sensor and the fuel tank 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.
The engine is running.
• | The PCM detects a voltage out of tolerance condition on the 5 volt reference B circuit. |
• | The above condition is present for longer than 10 seconds. |
• | The PCM does not illuminate the malfunction indicator lamp (MIL). |
• | The PCM stores the conditions that were present when the DTC set as Fail Records data only. This information will not be stored as Freeze Frame data. |
• | 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 or by disconnecting the PCM battery feed. |
Important: Inspect the PCM and engine grounds for being secure and clean.
Check 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 poor terminal to wire connection. Use a corresponding mating terminal to test for proper terminal tension. |
• | 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 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 occurs that caused the DTC to set. This may assist in diagnosing the condition.
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 Schematics . Was a problem found? | -- | ||
3 |
Does the scan tool display voltage more than the first specified value or less than the second specified value? | 4.8 V 0.1 V | Go to DTC P0530 Air Conditioning (A/C) Refrigerant Pressure Sensor Circuit | |
4 |
Is voltage more than the specified value? | 5.1 V | ||
5 |
Is teh voltage more than the specified value? | 5.1 V | ||
6 | Locate and repair short to voltage in the 5 volt reference B circuit. Is action complete? | -- | -- | |
7 | Is voltage less than the specified value indicated? | 4.9 V | ||
8 |
Was a problem found? | -- | ||
9 |
Was a problem found? | -- | ||
10 |
Is DTC P1635 set? | -- | ||
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/ProgrammingIs the action complete? | -- | -- | ||
12 | Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heater, Ventilation, and Air Conditioning (HVAC). Is the action complete? | -- | -- | |
13 |
Does the scan tool indicate DTC P1639 failed this ignition? | -- | System OK |