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 355 (ENGINE CONTROLS SELF-DIAGNOSTICS - 2.2L BI-FUEL)SELF-DIAGNOSTIC SYSTEMDIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS (ALTERNATIVE FUELS)DIAGNOSTIC 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 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
- Install a scan tool. Does the scan tool turn ON? If yes, go to next step. If no, see SCAN TOOL DOES NOT POWER UP under SYSTEM TESTS in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
- Attempt to establish communication with the listed control modules. If you are using a Tech 2, obtain the information with the Class 2 MESSAGE MONITOR feature:
- The Instrument Panel Cluster (IPC)
- The Powertrain Control Module (PCM)
- Body Control Module (BCM)
Does the scan tool communicate with all the listed control modules? If yes, go to next step. If no, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE under SYSTEM TESTS in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
- Verify the vehicle is operating on CNG. Attempt to start the engine. Does the engine start and idle? If yes, go to next step. If no, go to DTC P1204: VEHICLE DOES NOT OPERATE IN CNG MODE under DIAGNOSTIC TESTS.
- Select the DTC display function for the following control modules:
- The Body Control Module (BCM).
- The Electronic Brake Control Module (EBCM).
- The Instrument Panel Cluster (IPC).
- The Powertrain Control Module (PCM).
- The HVAC module.
Does the scan tool display any DTCs? If yes, go to next step. If no, go to step 9.
- Using a scan tool, select CAPTURED INFO to store the powertrain DTC information. Did you complete the action? If yes, go to next step.
- Does the scan tool display DTCs which begin with a "U"? If yes, go to SCAN TOOL DOES NOT COMMUNICATE WITH CLASS 2 DEVICE under SYSTEM TESTS in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If no, go to next step.
- Were any of the PCM DTCs P0601, P0602, P1209 or P1621 set? If yes, perform appropriate diagnostic procedure. Go to DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, go to next step.
- Does the scan tool display DTC P0562, P0563, P0621 or P0622? If yes, see appropriate GENERATORS & REGULATORS article in STARTING & CHARGING SYSTEMS. If no, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS .
- Start and idle the engine. Force a switch over to gasoline operation with the scan tool in the SPECIAL FUNCTIONS, OUTPUT CONTROLS menu. Does the engine continue to idle? If yes, go to next step. If no, go to next step.
- Is the customer's concern with the Transmission? If yes, see appropriate DIAGNOSIS article in AUTOMATIC TRANSMISSIONS. If no, go to next step.
- Is the customer's concern with the Inspection/Maintenance (I/M) testing? If yes, go to INSPECTION/MAINTENANCE SYSTEM CHECK under DRIVE CYCLES. If no, go to next step.
- If the customer's concern is a MIL related symptom, refer to appropriate INSTRUMENT PANELS article in ACCESSORIES & EQUIPMENT. Repair as necessary. Did you complete the action? If yes, system is okay. If no, problem is intermittent. See INTERMITTENTS in TROUBLE SHOOTING - 2.2L CAVALIER - BI-FUEL - CNG/GASOLINE article.
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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.