Circuit Description
The powertrain control module (PCM) provides 5 volts to the air conditioning (A/C) pressure sensor. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P1639 sets.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
| • | The PCM detects a voltage out of tolerance condition on the 5-volt reference circuit. |
| • | The above condition is present for longer than 10 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
Diagnostic Aids
If any sensor using a 5-volt bias voltage, such as the intake air temperature (IAT) sensor or fuel level sensor, is shorted to voltage, DTC P1635 may set in addition to DTC P1639.
For an intermittent condition, refer to Intermittent Conditions
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views | ||||
1 | Did you complete the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 |
Did the DTC fail this ignition? | -- | Go to Step 3 | Go to Diagnostic Aids |
3 |
Is the voltage within the specified range? | 4.8-5.2 V | Go to Step 9 | Go to Step 4 |
4 | Is the voltage measured in the previous step more than the specified value? | 5.2 V | Go to Step 5 | Go to Step 8 |
5 |
Is the voltage more than the specified value? | 0 V | Go to Step 6 | Go to Step 7 |
6 | Test the 5-volt reference circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | -- |
7 | Test the 5-volt reference circuit for a short to any other circuit within the harness to the PCM. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 |
8 |
Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 |
9 | Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement in Heating, Ventilation, and Air Conditioning. Did you complete the replacement? | -- | Go to Step 11 | -- |
10 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | -- | Go to Step 11 | -- |
11 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 12 |
12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
