GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2004 🢒 Monte Carlo 🢒 Engine 🢒 Engine Controls - 3.8L (L36 and L67) 🢒 DTC P0641

Circuit Description

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

    • The manifold absolute pressure (MAP) sensor
    • The exhaust gas recirculation (EGR) valve
    • The fuel tank pressure (FTP) sensor
    • The throttle position (TP) sensor

These 5-volt reference circuits are independent of each other outside the PCM, but are bussed together inside the PCM. Therefore 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.

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 more 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.

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-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

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
  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 in Wiring Systems.

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 the manifold absolute pressure (MAP) sensor.
  3. Command the EGR solenoid to 100 percent with a scan tool.
  4. Measure the voltage from the 5-volt reference circuit of the MAP sensor to a good ground with a DMM. Refer to Circuit Testing in Wiring Systems.

Is the voltage within the specified range?

4.8-5.2 V

Go to Intermittent Conditions

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. Refer to the appropriate replacement procedure below:
    3. • The MAP sensor--Refer to Manifold Absolute Pressure Sensor Replacement .
    • The fuel tank pressure (FTP) sensor--Refer to Fuel Tank Pressure Sensor Replacement .
    • The throttle position (TP) sensor. Refer to Throttle Position Sensor Replacement .

Was a component replaced?

--

Go to Step 13

Go to Step 7

7
  1. Turn OFF the ignition.
  2. Disconnect the powertrain control module (PCM).
  3. Test the 5-volt reference circuit for a short to ground or any sensor low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 13

Go to Step 12

8
  1. Monitor the DMM while disconnecting the MAP sensor and FTP sensor, one at a time. Refer to Engine Controls Component Views .
  2. If the voltage returns to within the specified value when one of the devices is disconnected, test that sensors signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

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 in Wiring Systems.

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 in Wiring Systems.

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 PCM. Refer to Powertrain Control Module Replacement .

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

System OK