Circuit Description
The PCM uses this 5 volt reference circuit as a sensor feed for the A/C refrigerant pressure sensor and the fuel tank pressure sensor. The PCM monitors the voltage on this 5 Volt Reference circuit. If the voltage is out of tolerance, the PCM will set DTC P1639.
Conditions for Running the DTC
The engine is running.
Conditions for Setting the DTC
| • | The PCM detects a voltage out of tolerance condition on this 5 Volt Reference circuit. |
| • | Above condition for more than 10 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC set as Freeze Frame/Failure Records data. |
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the malfunction indicator lamp (MIL) during the third consecutive trip in which the diagnostic has run and passed. |
| • | The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
Inspect for the following:
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.
Step | Action | Values | Yes | No | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||||||
2 | Visually/physically inspect the PCM and engine grounds. Ensure the grounds are clean and secure. Did you find and correct the condition? | -- | ||||||||||
3 |
Does the voltage measure at or near the specified value? | 5V | ||||||||||
4 |
Does the measured voltage remain at or near the specified value when each component is connected? | 5V | ||||||||||
5 |
Does the voltage measure at or near the specified value? | 5V | Go to Diagnostic Aids | |||||||||
6 | Is the voltage below the specified value? | 4.8V | ||||||||||
7 | Test the signal circuit of the effected component for a short to B+. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||||
8 | Test the signal circuit of the A/C pressure sensor for a short to B+. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||||
9 | Test the 5 volt reference circuit for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | ||||||||||
10 | 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? | -- | ||||||||||
11 | Replace the effected component. Did you complete the repair? | -- | -- | |||||||||
12 | Replace the A/C pressure sensor. Did you complete the repair? | -- | -- | |||||||||
13 |
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | |||||||||
14 |
Does the DTC reset? | -- | ||||||||||
15 | Does the scan tool indicate any DTCs set that you have not diagnosed? | -- | Go to applicable DTC | System OK |
