P0641 Code

[GEE EX PEER]

Our 2007 GXP has a P0641 code and on the trip computer it says loss of power, with an arrow pointing down. The car will vibrate when trying to accelerate. I looked up the code, but I don`t even know where to start diagnosing.
Any one ever have this problem?

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[TD]Your Vehicle: 2007 Pontiac Grand Prix V8-5.3L[/TD]
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[TD="class: right_vspacer_left"]Vehicle » A L L Diagnostic Trouble Codes ( DTC ) » Testing and Inspection » P Code Charts » P0641[/TD]
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[TD]DTC P0641 or P0651

DTC Descriptors

DTC P0641

• 5-Volt Reference 1 Circuit

DTC P0651

• 5-Volt Reference 2 Circuit

Diagnostic Fault Information

Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection\Initial Inspection and Diagnostic Overview

Circuit/System Description

The engine control module (ECM) has 2 internal 5-volt reference busses called 5-volt reference 1 and 5-volt reference 2. Each reference bus provides 5-volt reference circuits for more than one sensor. Therefore, a fault condition on one 5-volt reference circuit will affect the other 5-volt reference circuits connected to that reference bus. The ECM monitors the voltage on the 5-volt reference busses.

The 5-volt reference 1 bus provides 5 volts to the following sensors:

• The manifold absolute pressure (MAP) sensor
• The fuel tank pressure (FTP) sensor
• The air conditioning (A/C) refrigerant pressure sensor
• The accelerator pedal position (APP) sensor 2
• The engine oil pressure (EOP) sensor
• The camshaft position (CMP) sensor

The 5-volt reference 2 bus provides 5 volts to the following sensors:

• The APP sensor 1
• The throttle position (TP) sensor 1 and 2
• The crankshaft position (CKP) sensor
• The brake booster vacuum sensor

Conditions for Running the DTC

• The ignition is in Unlock, Accessory, Run, or Crank.
• The ignition voltage is more than 5.23 volts .
• DTCs P0641 and P0651 run continuously when the above conditions are met.

Conditions for Setting the DTC

The ECM detects a voltage out of tolerance condition on the 5-volt reference 1 or 2 bus for more than 0.5 second .

Action Taken When the DTC Sets

DTCs P0641 and P0651 are Type A DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0641 and P0651 are Type A DTCs.

Circuit/System Verification

Ignition ON, observe the scan tool 5-volt reference 1 and 2 parameters. The reading should display Circuit OK for a normally operating system.

Circuit/System Testing

Important: Additional DTCs may set when disconnecting components.

1. Ignition OFF, disconnect the harness connector of all the sensors connected to the 5-volt reference bus for the applicable DTC. Refer to Circuit/System Description.

Important: A short to voltage on the signal circuit of certain components may cause this DTC to set.

1. Ignition ON, test for 4.8-5.2 volts between one of the 5-volt reference circuits and ground.

• • If less than the specified range, test all of the 5-volt reference circuits for a short to ground. If all circuits test normal, replace the ECM.
  • If greater than the specified range, test for a short to voltage on all of the 5-volt reference circuits, or the signal circuit for each component associated with the appropriate 5-volt reference bus for a short to voltage. If all circuits test normal, replace the ECM.

1. Connect each component associated with the appropriate 5-volt reference bus, one at a time, while monitoring the voltage. The voltage should not change more than 1 volt .

• • If the voltage display changes more than the specified range when a component is connected, replace the component.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure. See: Verification Tests

• Accelerator Pedal Position Sensor Replacement
• Air Conditioning (A/C) Refrigerant Pressure Sensor Replacement
• Control Module References for ECM replacement, setup, and programming See: Testing and Inspection\Programming and Relearning
• Fuel Tank Pressure Sensor Replacement
• Manifold Absolute Pressure Sensor Replacement
• Throttle Body Assembly Replacement
• Engine Oil Pressure Sensor and/or Switch Replacement
• Camshaft Position Sensor Replacement
• Power Brake Booster Vacuum Sensor Replacement
• Crankshaft Position Sensor Replacement

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[Explicit_Spade]

- Faulty Engine Control Module (ECM)
- ECM harness is open or shorted
- ECM circuit poor electrical connection
- Shorted sensor on 5 volt circuit

 

[GEE EX PEER]

I found the problem. The ECT (engine coolant temperature) sensor is broken. This is why there is a loss of engine power. If this sensor gets damaged it affects the fuel control system, and the 5 volt bus to the ECM.
I found it when I was inspecting sensors around the engine, and I saw the ECT sensor has black tape wrapped around it. The sensor was very loose when I touched it. I removed the tape and found the sensor body for the wire connection is broken.
I now remember how this got like that. The idiot body shop did this when the front grill and radiator was replaced. They never bothered to tell us that they broke it and tried to do a quick fix by taping it. Morons.