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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 COIL TESTDIAGNOSTIC PROCEDURE
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Diagnostic Procedure

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedure
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. Observe the Engine Coolant Temperature (ECT) using a scan tool. Is the ECT value 50-90°F (10-32°C)? If yes, go to next step. If no, go to step  4.
  3. Disconnect the fuel injector multi-way harness connector. Measure the resistance of each fuel injector between the ignition feed circuit and the fuel injector control circuit, at the multi-way connector using a DMM. Do any of the fuel injectors display a resistance outside 11-14 ohms? If yes, go to step  5. If no, go to DIAGNOSTIC AIDS .
  4. Disconnect the fuel injector multi-way connector. Measure the resistance of each fuel injector between the ignition feed circuit and the fuel injector control circuit, at the multi-way connector using a DMM. Record each fuel injector value. Subtract the lowest resistance value from the highest resistance value. Is the difference equal to, or less than, 3 ohms? If yes, go to FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL  or FUEL INJECTOR BALANCE TEST WITH TECH 2  . If no, go to step  8.
  5. Remove the upper intake manifold. Go to appropriate article in ENGINES. Did you complete the action? If yes, go to next step.
  6. Measure the resistance of the ignition 1 voltage circuit between the multi-way connector and the affected fuel injector connector, using a DMM. Is the resistance more than 5 ohms? If yes, go to next step. If no, go to step  9.
  7. Repair the open or high resistance in the ignition 1 voltage circuit. After repair, go to step  11.
  8. Add all of the fuel injector resistance values, to obtain a total resistance value. Divide the total resistance value by the number of fuel injectors, to obtain an average resistance value. Subtract the lowest and the highest individual fuel injector resistance values from the average resistance value. Replace the fuel injector that displays the greatest resistance difference, above or below the average. After repair, go to step  11.
  9. Test for an intermittent and for a poor connection at the affected fuel injector. Did you find and correct the condition? If yes, go to step  11. If no, go to next step.
  10. Replace any fuel injectors that measured out of specification. After repair, go to step  11.
  11. 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  2.
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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.