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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1022 (Engine Controls Diagnosis - 6.6L (Lb7) (DTCS P0612 To P2141)) >> Diagnosis >> DTC P0641 >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The number below refers to the step number on the diagnostic table.

  1. 8:  A short to the transmission control module (TCM) MIL request may not show up on the scan tool as skewed sensor readings. The TCM momentarily grounds the circuit as a test, and the test is just long enough to set this DTC.
DTC P0641

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference:  Engine Control Module (ECM) Connector End Views  or  Engine Controls Connector End Views 
1 Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic Trouble Code (DTC) List
2
  1. Observe the Freeze Frame/Failure Records data 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.
Does the DTC fail this ignition?		 - Go to Step 3  Go to Intermittent Conditions
3
  1. Turn OFF the ignition.
  2. Disconnect the accelerator pedal position (APP) sensor.
  3. Turn ON the ignition, with the engine OFF.
  4. Using a DMM, measure the voltage between the 5-volt reference circuit of the APP sensor 1 and the APP sensor 3 and a good ground.
Is the voltage within the specified range?		 4.8 - 5.2 V Go to Step 5  Go to Step 4 
4 Does the voltage measure more than the specified value? 5.2 V Go to Step 8  Go to Step 6 
5
  1. Reconnect the APP sensor.
  2. Disconnect the fuel rail pressure (FRP) sensor.
  3. Using a DMM, measure the voltage between the FRP sensor 5-volt reference circuit and a good ground.
Is the voltage within the specified range?		 4.8 - 5.2 V Go to Intermittent Conditions Go to Step 9 
6
  1. Monitor DMM while disconnecting the FRP sensor.
  2. If voltage changes when the sensors is disconnected, replace FRP sensor. Refer to Fuel Rail Pressure (FRP) Sensor Replacement .
Did you find and correct the condition?		 - Go to Step 11  Go to Step 7 
7
  1. Turn OFF the ignition.
  2. Disconnect the ECM.
  3. Test the 5-volt reference circuit for the following conditions. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
    • A short to ground
    • A short to any low reference circuit
    • A short to the fuel pressure regulator control circuit
    • A short to the TCM MIL request circuit
    • A short to the ignition 1 relay control circuit
Did you find and correct the condition?		 - Go to Step 11  Go to Step 10 
8  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 11  Go to Step 10 
9 Replace the APP sensor. Refer to Accelerator Pedal Position (APP) Sensor Replacement .
Did you complete the replacement?		 - Go to Step 11  -
10 Replace the ECM. Refer to Engine Control Module (ECM) Replacement .
Did you complete the replacement?		 - Go to Step 11  -
11
  1. Use a scan tool to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?		 - Go to Step 12  Go to Step 2 
12 With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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