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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 557 (STARTING SYSTEM)ON-VEHICLE TESTINGENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Engine Electrical Diagnostic System Check

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Engine Electrical Diagnostic System Check
WARNING: This page does not describe the selected car, but rather 12 other vehicles, including the 2003 GMC Yukon XL, 2003 GMC Yukon, 2003 GMC Sierra, 2003 GMC Cab & Chassis Sierra, and 2003 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Battery Inspection/Test? If so, go to next step. If not, go to BATTERY TESTING & INSPECTION (NON-HP2) .
  2. Install a scan tool. Does the scan tool power up? If so, go to step  4. If not, go to SCAN TOOL DOES NOT POWER UP .
    NOTE: The engine may start during the following step. Turn off the engine as soon as you have observed the Crank power mode.
  3. Access the Class 2 Power Mode in the Diagnostic Circuit Check on the scan tool. Rotate the ignition switch through OFF, RUN, and CRANK positions while observing the Class 2 Power Mode on the scan tool. Does the Class 2 Power Mode reading match the ignition switch positions for OFF, RUN and CRANK positions? If so, go to next step. If not, go to POWER MODE MISMATCH .
  4. Lack of communication may be due to a partial malfunction of the class 2 serial data circuit or due to a total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition. Turn ON the ignition, with the engine OFF. Attempt to communicate with each module on the Class 2 serial data circuit. If using a Tech 2, obtain this information using the Class 2 Message Monitor feature. Does the scan tool communicate with any module on the Class 2 serial data circuit? If so, go to next step. If not, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE
  5. The symptom list in Symptoms will determine the correct diagnostic procedure to use. Select the Display DTCs function for each module. If using a Tech 2, use the Class 2 DTC Check feature in order to determine which modules have DTCs set. Record all of the displayed DTCs the DTC status and the module which set the DTC. Does the scan tool display any DTCs? If so, go to next step. If not, go to ENGINE ELECTRICAL SYMPTOMS .
  6. The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed. Does the scan tool display any DTC beginning with "U"? If so, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If not, go to next step.
  7. Does the scan tool display any DTC beginning with "P"? If so, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If not, go to next step.
  8. Does the scan tool display any DTC beginning with "B"? If so, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in appropriate SELF-DIAGNOSTICS article. If not, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in in appropriate SELF-DIAGNOSTICS article .
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.