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 86 (ENGINE CONTROLS - SELF-DIAGNOSTICS - 3.0L)SELF-DIAGNOSTIC SYSTEMVEHICLE ON-BOARD DIAGNOSTIC SYSTEM CHECK
1999 GMC Forward Control 5.7 R, Automatic
Vehicle On-Board Diagnostic System Check
1999 GMC Forward Control 5.7 R, AutomaticSECTION Vehicle On-Board Diagnostic System Check
WARNING: This page is about a different car, the 2002 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Tech 2 scan tool is required to perform powertrain diagnostic system check.
Powertrain diagnostic system check determines:
- If Malfunction Indicator Light (MIL) operates.
- If ECM is operating and can recognize a fault.
- If any DTCs are stored.
- Connect scan tool to 16-pin DLC located under left side of instrument panel. See Figure . If scan tool does not power up, see SCAN TOOL DOES NOT POWER UP in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If scan tool powers up, go to next step.
- Establish communication with BCM, SDM, IPC, auto climate control and OnStar modules (if equipped). If scan tool communicates with any module, go to next step. If scan tool does not communicate with any module, see SCAN TOOL DOES NOT COMMUNICATE WITH CLASS-2 DEVICES in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. go to next step.
- Establish communication with ECM, TCM and EBTCM (if equipped). If scan tool communicates with any module, go to next step. If scan tool does not communicate with any module, see SCAN TOOL DOES NOT COMMUNICATE WITH KEYWORD DATA LINE in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT.
- Check all modules for DTCs. If any DTCs are set in BCM, see appropriate test under DIAGNOSTIC TESTS in appropriate BODY CONTROL MODULES article in ACCESSORIES & EQUIPMENT. If no DTCs are set in BCM, go to next step.
- If DTCs are set in ECM or TCM, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are set in ECM, go to next step.
- If DTCs are present in EBTCM, see DIAGNOSTIC TESTS in appropriate ANTI-LOCK/TCS article. If no DTCs are present in EBTCM, go to next step.
- If DTCs are present in auto climate control module, see appropriate AUTOMATIC A/C-HEATER SYSTEMS article in AIR CONDITIONING & HEATING. If no DTCs are present in auto climate control module, go to next step.
- If engine starts and runs, diagnostic system check is complete. If problem exists, observe scan tool data and/or refer to symptom in appropriate TROUBLE SHOOTING - NO CODES article. If engine does not start and run, see appropriate BASIC DIAGNOSTIC PROCEDURES 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.