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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 385 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING - 3.4L)FUEL SYSTEMSFUEL INJECTOR CIRCUIT DIAGNOSISDIAGNOSTIC PROCEDURES
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Diagnostic Procedures

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS in SELF-DIAGNOSTICS - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article. After performing diagnostic system check - engine controls, go to next step.
  2. Are any fuel injector DTCs set? If yes, go to DTC P0201-P0206: INJECTOR CONTROL CIRCUIT under DIAGNOSTIC TESTS in SELF-DIAGNOSTICS - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article. If yes, go to step  4. If no, go to next step.
  3. Check the fuel injector fuse (15-amp), located in the bottom underhood junction block. See Fig 1. Is the fuel injector fuse open? If yes, go to next step. If no, go to step  6.
  4. Turn ignition switch to OFF position. Disconnect the fuel injector multi-way harness connector. Probe the fuel injector ignition 1 voltage circuit, fuse side, using a test light connected to battery voltage. Does the test light illuminate? If yes, go to step  9. If no, go to next step.
  5. Turn ignition switch to RUN position, engine OFF. Does the test light illuminate? If yes, go to step  13. If no, go to step  8.
  6. Turn ignition switch to OFF position. Disconnect the fuel injector multi-way harness connector. Turn ignition switch to RUN position, engine OFF. Probe the fuel injector ignition 1 voltage circuit, fuse side, using a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step  10.
  7. Test for continuity between the ignition voltage terminal and a fuel injector terminal, at the multi-way harness connector, fuel injector side. Does the DMM display a resistance above 5 ohms? If yes, go to step  11. If no, go to step  12.
  8. Test the fuel injector ignition 1 voltage circuit, between the multi-way harness connector and the fuel injectors for a short to ground. Did you find and correct the condition? If yes, go to step  14. If no, go to INTERMITTENTS in TROUBLE SHOOTING - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.
  9. Repair the short to ground in the fuel injector ignition voltage circuit. After repair, go to step  14.
  10. Repair the open in the ignition 1 voltage between UBEC and the multi-way connector. After repair, go to step  14.
  11. Repair the fuel injectors ignition 1 voltage circuit for an open and/or high resistance, between the multi-way connector and the splice. After repair, go to step  14.
  12. Repair the poor connection at the multi-way connector. After repair, go to step  14.
  13. Repair the short to a PCM ground in the fuel injector ignition voltage circuit. After repair, go to step  14.
  14. Operate the system to verify the repair. Did you correct the condition? If yes, system is okay at this time. If no, go to step  3.
Fig 1: Identifying Bottom Underhood Fuse Block Fuses & Relays
G00226962Courtesy of GENERAL MOTORS CORP.
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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.