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HOMESERVICE MANUALSCHEVROLET2008CHEVY EXPRESS G2500, VAN CARGO, 6.6 6REPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 708 (ANTILOCK BRAKE SYSTEM WITH TRACTION CONTROL SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC C0298 OR P0856TEST DESCRIPTION
2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6

Test Description

2008 Chevrolet Chevy Express G2500, Van Cargo, 6.6 6SECTION Test Description
WARNING: This page is about a different car, the 2006 GMC Sierra, 2006 GMC Cab & Chassis Sierra, 2006 Chevrolet Silverado, and 2006 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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

Step Action Values Yes No
Schematic Reference: ABS Schematics 
Connector End-View Reference: ABS Connector End Views 
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
2 If DTCs set for the Parallel Hybrid Truck (PHT), C0035 or U0415, C0055 or C003D, C0245 or C0078, and C0550 or C0570, diagnose these DTC first.
Is only 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 . 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 .
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 .
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 .
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 .
Did you find and correct the condition?		 - Go to Step 14  Go to Step 13 
12 Replace the PCM. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 - Go to Step 14  -
13 Replace the EBCM. Refer to Control Module References for replacement, setup, and programming.
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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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.