Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 115 (ENGINE CONTROLS SELF-DIAGNOSTICS)DIAGNOSTIC TESTSDTC P0403: EGR VALVE CONTROL CIRCUITDIAGNOSTIC 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 2002 Pontiac Montana, 2002 Oldsmobile Silhouette, and 2002 Chevrolet Venture. However, it is still accessible from the selected car via links, so may be relevant.
- Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM.
- Install a scan tool. Turn ON the ignition, with the engine OFF. With a scan tool, command the EGR from 0 percent to 100 percent. Does the EGR position sensor remain close to the Desired EGR Position at all commanded positions? If yes, go to next step. If no, go to step 4.
- Observe the Freeze Frame/Failure Records data for this DTC. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC, or within the observed parameters of the Freeze Frame/Failure Records. Does the DTC fail this ignition cycle? If yes, go to next step. If no, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.
- Turn OFF the ignition. Disconnect the EGR. Turn ON the ignition, with the engine OFF. Probe the EGR valve high control circuit with a test lamp connected to a good ground. With a scan tool, command the EGR between 0-10 percent. Does the test lamp turn ON and OFF with each command? If yes, go to next step. If no, go to step 6.
- Connect a test lamp between the EGR valve high control circuit and the EGR valve low control circuit. With a scan tool, command the EGR between 0-10 percent. Does the test lamp turn ON and OFF with each command? If yes, go to step 10. If no, go to step 9.
- Does the test lamp remain illuminated with each command? If yes, go to step 8. If no, go to next step.
- Test the EGR valve high control circuit for a short to ground or an open. Did you find and correct the condition? If yes, go to step 14. If no, go to step 11.
- Test the EGR valve high control circuit for a short to voltage. Did you find and correct the condition? If yes, go to step 14. If no, go to step 11.
- Test the EGR valve low control circuit for an open or high resistance. Did you find and correct the condition? If yes, go to step 14. If no, go to step 11.
- Inspect for poor connections at the harness connector of the EGR valve. Did you find and correct the condition? If yes, go to step 14. If no, go to step 12.
- Inspect for poor connections at the harness connector of the PCM. Did you find and correct the condition? If yes, go to step 14. If no, go to step 13.
- Replace the EGR valve. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step 14.
- Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE under PROGRAMMING. After repairs, go to next step.
- Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to step 2.
- Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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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.