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 MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 79 (ENGINE CONTROL SYSTEM SELF-DIAGNOSTICS - 3.4L)DIAGNOSTIC TESTSDTC P0443: EVAP PURGE SOLENOID CONTROL CIRCUITDIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic
Diagnostic Procedures
1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page is about a different car, the 2002 Pontiac Grand Am, 2002 Oldsmobile Alero, 2002 Chevrolet Monte Carlo, and 2002 Chevrolet Impala. However, it is still accessible from the selected car via links, so may be relevant.
- Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
- Turn ignition on, with engine off. With a scan tool, command the EVAP purge valve to 50 percent and then to 0 percent. Do you hear or feel a clicking from the EVAP purge valve when the valve is commanded to 50 percent? If yes, go to next step. If no, go to step 4.
- Review the Freeze Frame/Failure Records data for this DTC. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC or as close to the Freeze Frame/Failure Records data that you observed. See CONDITIONS FOR RUNNING DTC . Does the DTC fail this ignition? If yes, go to next step. If no, see INTERMITTENT CONDITIONS under SELF-DIAGNOSTIC SYSTEM.
- Turn ignition off. Disconnect the EVAP purge valve harness connector. Turn ignition on, with engine off. Probe the ignition voltage circuit at the EVAP purge valve harness connector with a test light connected to a good ground. Does the test light illuminate? If yes, go to next step. If no, go to step 11.
- Connect a test light between the control circuit and the ignition voltage circuit of the EVAP purge valve harness connector. With a scan tool, command the EVAP purge valve to 0 percent. Does the test light illuminate? If yes, go to step 8. If no, go to next step.
- With a scan tool, command the EVAP purge to 50 percent. Does the test light illuminate or pulse when the EVAP purge valve is commanded to 50 percent? If yes, go to step 9. If no, go to next step.
- Test the control circuit of the EVAP purge valve for an open or short to voltage. Did you find and correct the condition? If yes, go to step 14. If no, go to step 10.
- Test the control circuit of the EVAP purge valve for a short to ground. Did you find and correct the condition? If yes, go to step 14. If no, go to step 13.
- Inspect for poor connections at the harness connector of the EVAP purge 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 control module. Did you find and correct the condition? If yes, go to step 14. If no, go to step 13.
- Repair the ignition voltage circuit of the EVAP purge valve. After repairs, go to step 14
- Replace the EVAP purge valve. After repairs, go to step 14
- Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE under PROGRAMMING. After replacing PCM, go to next step.
- Use the scan tool in order to clear the DTCs. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step 2.
- Using scan tool, observe stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are displayed, 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.