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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1479 (ANTILOCK BRAKE SYSTEM, TRACTION CONTROL SYSTEM & STABILITY CONTROL SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC C1221-C1235TEST DESCRIPTION
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Test Description

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Test Description
WARNING: This page is about a different car, the 2004 Chevrolet Corvette. 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. 3:  Measure the resistance of the wheel speed sensor in order to determine if the sensor has a valid resistance value.
  2. 4:  Ensures that the wheel speed sensor is generating a valid AC voltage output.
DTC C1221-C1235

Step Action Values Yes No
Schematic Reference:  ABS Schematics  
Connector End View Reference:  ABS Connector End Views  
1 Did you perform the ABS Diagnostic System Check? - Go to Step 2  Go to Diagnostic System Check - ABS 
2
  1. Install a scan tool.
  2. Turn ON the ignition.
  3. Set up the scan tool snap shot feature to trigger for this DTC.
  4. Drive the vehicle at a speed greater than the specified value.
Does the scan tool indicate that this wheel speed DTC set?		 8 km/h (5 mph) Go to Step 3  Go to Diagnostic Aids
3 
  1. Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  2. Disconnect the wheel speed sensor connector.
  3. Measure the resistance across the wheel speed sensor.
Does the resistance measure within the specified range?		 850-1350 Ω Go to Step 4  Go to Step 8 
4 
  1. Spin the wheel.
  2. Measure the AC voltage across the wheel speed sensor.
Does the AC voltage measure greater than the specified value?		 100 mV Go to Step 5  Go to Step 8 
5 Inspect for poor connections at the harness connector of the wheel speed sensor. 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 10  Go to Step 6 
6
  1. Disconnect the EBCM harness connector.
  2. Install the J 39700 universal pinout box using the J 39700-300  cable adapter to the EBCM harness connector only. See Special Tools and Equipment .
  3. Test the wheel speed sensor circuits for the following:
    • An open
    • A short to ground
    • A short to voltage
    • Shorted together
Refer to Circuit Testing and Wiring Repairs in Wiring Systems.Did you find and correct the condition?		 - Go to Step 10  Go to Step 7 
7 Inspect for poor connections at the harness connector for 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 10  Go to Step 9 
8 Replace the wheel speed sensor. Refer to Wheel Bearing/Hub Replacement - Front in Front Suspension or Wheel Bearing/Hub Replacement - Rear in Rear Suspension.
Did you complete the replacement?		 - Go to Step 10  -
9 Replace the EBCM. Refer to Electronic Brake Control Module Replacement .
Did you complete the repair?		 - Go to Step 10  -
10
  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
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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.