SYS.OK|MANUAL.DB● LIVE
HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 143 (ENGINE CONTROLS - SYSTEM & COMPONENT TESTING)FUEL SYSTEM (BI-FUEL & CNG)FUEL INDICATOR LIGHT ALWAYS ON - ALTERNATIVE FUELSDIAGNOSTIC PROCEDURE
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Diagnostic Procedure

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Diagnostic Procedure
WARNING: This page does not describe the selected car, but rather 31 other vehicles, including the 2002 Saturn Vue, 2002 Pontiac Montana, 2002 Pontiac Aztek, 2002 Oldsmobile Silhouette, and 2002 Oldsmobile Bravada. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article. After performing Alternative Fuels Diagnostic System Check - Engine Controls, go to next step.
  2. Start and idle engine. Is Fuel Indicator Light (FIL) illuminated? If yes, go to next step. If no, go to INTERMITTENTS in TROUBLE SHOOTING - NO CODES - TRUCKS article.
  3. Observe operation of other Instrument Panel (IP) gauges and/or lights. Do all IP indicators, except FIL, operate correctly? If yes, go to next step. If no, perform Diagnostic System Check - Instrument Cluster. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
  4. With scan tool, communicate with AF ECM and observe AFO Signal and AFO Signal Command data parameters. Observe data parameters as you crank and start engine. Do both data parameters indicate AF ECM is in control of engine fueling? If yes, go to next step. If no, go to FUEL SYSTEM UNWANTED SWITCH TO GASOLINE (BI-FUEL ONLY) 
  5. Turn OFF the ignition. Disconnect PCM connectors. Turn ON the ignition, with the engine OFF. Is fuel indicator light illuminated? If yes, go to next step. If no, go to step  7.
  6. Test FIL Control circuit between PCM connector terminal and IP for a short to ground. Did you find and correct the condition? If yes, go to step  8. If no, perform Diagnostic System Check - Instrument Cluster. See appropriate ANALOG INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT.
    7. NOTE: When replacing PCM, Bi-fuel (LQ4/KL6) models require a switchover to gasoline with scan tool in order to perform Crankshaft Position Variation Learn Procedure. CNG only (LQ4/KL8) models DO NOT require Crankshaft Position Variation Learn Procedure.
  7. Replace PCM. Perform PCM relearn procedures. See PROGRAMMING in appropriate SELF-DIAGNOSTICS article. After repairs, go to next step.
  8. Remove all test equipment except scan tool. Connect any disconnected components, fuses, etc. With scan tool, clear DTC information from AF ECM and PCM. Turn the ignition OFF and wait 30 seconds. Observe FIL. Start engine and operate vehicle. Does FIL operate for a 2 second bulb check and then turn OFF? If yes, system is okay. If no, perform Alternative Fuels Diagnostic System Check - Engine Controls. See ALTERNATIVE FUELS DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM in appropriate SELF-DIAGNOSTICS article.
RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

Shop Manual-Ready ToolsFree Quote CheckQuote Shield Pro

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.