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 89 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 4.0L)INSPECTION/MAINTENANCE PROCEDURESINSPECTION/MAINTENANCE SYSTEM CHECKDIAGNOSTIC 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 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Many DTC related repairs will instruct the technician to clear the DTC information. This procedure will reset all of the I/M System Status indicators to NO, and require performing the I/M Complete System Set Procedure.
- Perform DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS under SELF-DIAGNOSTIC SYSTEM. Repair any DTCs or driveability concerns that would prevent the I/M System Status tests from completing. Did you find and repair a DTC or driveability concern? If yes, go to step 3. If no, go to next step.
- Check for applicable Technical Service Bulletins (TSB) for software updates that may prevent Inspection/Maintenance (I/M) readiness. Perform any reprogramming or repairs indicated by TSBs. Was a reprogramming or repair service required? If yes, go to INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE . If no, go to next step.
- Using scan tool, observe I/M system status display. Is more than one test indicating a NO status? If yes, go to INSPECTION/MAINTENANCE COMPLETE SYSTEM SET PROCEDURE . If no, perform appropriate I/M system set procedure for indicated system.
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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.