GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2005 🢒 Grand Prix 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 DTC P0641

Circuit Description

The powertrain control module (PCM) may provide 5 volts to the following sensors:

    • The manifold absolute pressure (MAP) sensor
    •  The air conditioning (A/C) refrigerant pressure sensor
    •  The exhaust gas recirculation (EGR) valve
    •  The fuel tank pressure (FTP) sensor
    •  The secondary AIR pressure sensor (L26, NU3 only)

A circuit condition on one sensor 5-volt reference circuit may affect the other sensor 5-volt reference circuits. The PCM monitors the voltage on the 5-volt reference circuit. If the PCM detects that the voltage is out of tolerance, DTC P0641 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0641 5-Volt Reference 1 Circuit

Conditions for Running the DTC

The Ignition is ON.

Conditions for Setting the DTC

The 5-volt reference 1 voltage is more than 4.7 volts or less than 4.4 volts for longer than 10 seconds.

This diagnostic runs continuously.

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 sensor, is shorted to voltage, DTC P0651 may set in addition to DTC P0641.
    • For an intermittent condition, refer to Testing for Intermittent Conditions and Poor Connections .

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 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 Diagnostic Aids

3
  1. Turn OFF the ignition.
  2. Disconnect the exhaust gas recirculation (EGR) valve.
  3. Turn ON the ignition, with the engine OFF.
  4. Command the EGR solenoid to 100 percent with a scan tool.
  5. Measure the voltage from the 5-volt reference circuit to a good ground with a DMM. Refer to Circuit Testing .

Is the voltage within the specified range?

4.8-5.2 V

Go to Step 5

Go to Step 4

4

Is the voltage measured in the previous step more than the specified value?

5.2 V

Go to Step 8

Go to Step 6

5
  1. Connect the EGR valve.
  2. Disconnect a sensor associated with the same 5 volt reference
  3. Command the EGR solenoid to 100 percent with a scan tool.
  4. Measure the voltage from the 5-volt reference circuit to a good ground with a DMM. Refer to Circuit Testing .

Is the voltage within the specified range?

4.8-5.2 V

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 11

6
  1. Monitor a DMM while disconnecting all other devices connected to the 5-volt reference circuit, one at a time. Refer to Engine Controls Component Views .
  2. If voltage changes when one of the devices are disconnected, replace the component.

Was a component replaced?

--

Go to Step 13

Go to Step 7

7

Test this 5-volt reference circuit for a short to ground or any sensor low reference circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

8
  1. Monitor the DMM while disconnecting the sensor associated with the 5 volt reference one at a time. Refer to Engine Controls Connector End Views .
  2. If the voltage returns to within the specified value when one of the devices is disconnected, test that sensor signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

4.8-5.2 V

Go to Step 13

Go to Step 9

9

Test the 5-volt reference circuits for a short to voltage. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 10

10

Test for a short between the EGR 5-volt reference circuit and the EGR solenoid high control circuit. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

11

Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .

Did you complete the replacement?

--

Go to Step 13

--

12

Replace the powertrain control module (PCM). Refer to Control Module References for replacement, setup, and programming.

Did you complete the replacement?

--

Go to Step 13

--

13
  1. Clear the DTCs with a scan tool.
  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 2

Go to Step 14

14

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