Refer to Engine Controls Schematics .
Circuit Description
The PCM uses the 5 Volt Reference B circuit as a sensor feed to the A/C 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. |
| • | Above condition for longer than 30 seconds. |
Diagnostic Aids
Inspect for the following conditions:
Many situations may lead to an intermittent condition. Perform each inspection or test as directed.
Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.
| • | Loose terminal connection |
| - | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| - | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair. |
| • | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
| • | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair. |
If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.
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 On Board (OBD) System Check? | -- | ||
2 |
Does the voltage measure more than the specified value? | 5.0V | ||
3 |
Does the voltage measure more than the specified value? | 0.0V | ||
4 | Is voltage less than the specified value? | 4.9 V | ||
5 | Repair short to voltage in the 5 Volt Reference circuit. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | -- | |
6 | Repair short to ground in the 5 Volt Reference circuit. Refer to in Wiring Systems. Did you find and correct the condition? | -- | ||
|
Important:: The PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | ||
8 | Replace the A/C pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation, and Air Conditioning. Did you complete the replacement? | -- | -- | |
9 |
Does the DTC reset? | -- | System OK |
