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Home >> GMC >> 2002 >> Jimmy 2D Utility, Part Time, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 1415 (Antilock Brake System And Traction Control System) >> Diagnostic Information and Procedures >> DTC C0298 or P0856: Requested Torque Signal Circuit >> Test Description

Test Description

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The numbers below refer to the step numbers on the diagnostic table.

  1. 4:  This step tests for voltage supplied to the EBCM from the PCM.
  2. 5:  This step tests for a shorted resistor in the PCM or a short to voltage within the requested torque circuit by verifying that a large voltage drop occurs when a test lamp is connected in parallel with the DMM.
DTC C0298 or P0856 Diagnostic Test

Step Action Values Yes No
Schematic Reference:  ABS Schematics  
Connector End View Reference:  ABS Connector End Views  
1 Did you perform the antilock brake system (ABS) Diagnostic System Check? - Go to Step 2  Go to Diagnostic System Check - ABS 
2 Is DTC P0856 set? - Go to Step 3  Go to Diagnostic Aids
3
  1. Use a scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
  3. Does DTC P0856 set?
 - Go to Step 4  Go to Diagnostic Aids
4 
  1. Turn OFF the ignition.
  2. Disconnect from the electronic brake control module (EBCM), the harness connector containing the requested torque signal circuit.
  3. Turn ON the ignition.
  4. Use a DMM in order to measure the voltage between the requested torque signal circuit and a good ground.
Does the voltage measure greater than the specified value?		 4.75 V Go to Step 5  Go to Step 8 
5 
  1. With the DMM still connected to monitor the requested torque signal circuit, connect one end of a test lamp to a good ground.
  2. Connect the other end of the test lamp to the positive lead of the DMM.
Does the voltage measure less than the specified value?		 0.15 V Go to Step 6  Go to Step 9 
6
  1. Turn OFF the ignition.
  2. Install a J 39700  Universal Breakout Box and a J 39700-325  Adapter Cable. See Special Tools and Equipment . Install the equipment between the EBCM and the EBCM harness connector.
  3. Start the engine.
  4. Use the DMM in order to measure the Hz frequency of the requested torque signal.
Does the Hz frequency of the requested torque signal measure within the specified range?		 121-134 Hz Go to Step 7  Go to Step 11 
7 Use the DMM in order to measure the duty cycle of the requested torque signal circuit.
Does the duty cycle of the requested torque signal measure within the specified range?		 40-95% Go to Step 12  Go to Step 13 
8 Test the requested torque signal circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 14  Go to Step 10 
9 Test the requested torque signal circuit 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 14  Go to Step 12 
10 Inspect for poor connections at the harness connector of the powertrain control module (PCM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 14  Go to Step 12 
11 Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 14  Go to Step 13 
12
IMPORTANT: Perform the setup procedure for the PCM.
Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls - 4.8L, 5.3L and 6.0L.Did you complete the replacement?		 - Go to Step 14  -
13
IMPORTANT: Following EBCM replacement, use the scan tool to perform Tire Size Calibration procedure.
Replace the EBCM. Refer to Electronic Brake Control Module Replacement .Did you complete the replacement?		 - Go to Step 14  -
14
  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does DTC P0856 reset?		 - Go to Step 4  System OK
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