For 1990-2009 cars

### Circuit Description

The powertrain control module (PCM) uses the 5-volt reference circuit as a sensor feed to the following sensors:

• | The A/C pressure sensor

• | The throttle position (TP) sensor 1

• | The accelerator pedal position (APP) sensor 2

• | The fuel tank pressure (FTP) sensor

• | The supercharge inlet pressure (SCIP) sensor

• | The barometric pressure (BARO) sensor

• | The camshaft position (CMP) sensor

The PCM monitors the voltage on the 5-volt reference circuit. If the voltage is out of tolerance, the PCM will set DTC P0641.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0641 5-Volt Reference 1 Circuit

### Conditions for Running the DTC

• | DTCs P0601, P0602, P0604, P0606, P1621, and P2610 are not set.

• | The ignition is in unlock, accessory, run, or crank mode.

• | The ignition voltage is greater than 5.2 volts.

• | DTC P0641 runs continuously when the above conditions are met.

### 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 1 second.

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/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.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 3

Go to Intermittent Conditions

3 | Visually and physically inspect the powertrain control module (PCM) and engine grounds. Ensure that the grounds are clean and secure. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 4
4 |

1. Turn OFF the ignition.
2. Disconnect the supercharge inlet pressure (SCIP) sensor.
3. Turn ON the ignition, with the engine OFF.
4. Measure the voltage from the 5-volt reference circuit of the A/C refrigerant pressure sensor harness connector to a good ground with a DMM. Refer to Circuit Testing and Wiring Repairs .

Is the voltage within the specified range?

4.8-5.2 V

Go to Step 6

Go to Step 5

5 | Is the voltage more than the specified value? | 5.2 V | Go to Step 9 | Go to Step 7
6 |

1. Connect the SCIP sensor.
2. Disconnect the accelerator pedal position sensor.
3. Measure the voltage from the 5-volt reference circuit of the accelerator pedal position sensor 2 harness connector to a good ground with a DMM. Refer to Circuit Testing and Wiring Repairs .

Is the voltage within the specified range?

4.8-5.2 V

Go to Intermittent Conditions

Go to Step 11

7 |

1. Observe the DMM while disconnecting all other devices that are connected to the 5-volt reference 1 circuit, one at a time.
2. If the voltage changes when one of the components are disconnected, replace the component. Refer to the appropriate replacement procedure below:

• | Manifold Absolute Pressure Sensor Replacement for SCIP sensor replacement

• | Camshaft Position Sensor Replacement

• | Barometric Pressure Sensor Replacement

• | Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement

• | Fuel Tank Pressure Sensor Replacement

• | Throttle Body Assembly Replacement

Was a component replaced?

--

Go to Step 12

Go to Step 8

8 | Test the 5-volt reference 1 circuits for a short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 12 | Go to Step 10
9 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Turn ON the ignition, with the engine OFF.
4. Test the following circuits for a short to voltage:

• | The 5-volt reference 1 circuits

• | The barometric pressure (BARO) sensor signal circuit

• | The fuel tank pressure (FTP) sensor signal circuit

• | The A/C refrigerant pressure sensor signal circuit

• | The SCIP sensor signal circuit--Refer to Circuit Testing and Wiring Repairs

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

10 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 12 | --
11 | Replace the A/C refrigerant pressure sensor. Refer to Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 12 | --
12 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 60 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 3

Go to Step 13

13 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK