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HOMESERVICE MANUALSPONTIAC2008GRAND PRIX BASEREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 40 (ANTILOCK BRAKE SYSTEM WITH TCS)DIAGNOSTIC INFORMATION AND PROCEDURESDTC C0121TEST DESCRIPTION
2008 Pontiac Grand Prix Base

Test Description

2008 Pontiac Grand Prix BaseSECTION Test Description
WARNING: This page is about a different car, the 2007 Hummer H2. However, it is still accessible from the selected car via links, so may be relevant.

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

  1. 2:  This step determines if the DTC is current.
DTC C0121

Step Action Yes No
Schematic Reference: Antilock Brake System Schematics 
Connector End View Reference: Antilock Brake System Connector End Views 
1 Did you perform the Diagnostic System Check - Vehicle? Go to Step 2  Go to Diagnostic System Check - Vehicle
2 
  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Use the scan tool in order to clear the DTCs.
Does the DTC reset?		 Go to Step 3  Go to Diagnostic Aids
3
  1. Connect the J 39700  Universal Pinout Box using the J 39700-530  cable adapter to the electronic brake control module (EBCM) harness connector only. See Special Tools .
  2. Test the battery positive voltage circuit for an open, high resistance, or a short to ground. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 Go to Step 5  Go to Step 4 
4 Replace the EBCM. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 Go to Step 5  -
5
  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 the DTC reset?		 Go to Step 2  System OK
RENDER: 1.0x

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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.