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 30 (HVAC SYSTEMS - AUTOMATIC)SYMPTOM TESTSTEST D: BLOWER MOTOR ALWAYS ON
1999 GMC Forward Control 5.7 R, Automatic
Test D: Blower Motor Always On
1999 GMC Forward Control 5.7 R, AutomaticSECTION Test D: Blower Motor Always On
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.
- Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM. After performing system check, go to next step.
- Turn ignition on, engine off. Turn off all HVAC controls. If Blower Motor operates, go to next step. If Blower Motor does not operate, inspect for intermittent loose wires or poor connectors to blower. See INTERMITTENTS under TROUBLE SHOOTING. Repair any damage or loose connections found.
- Connect scan tool. Observe COMMAND BLOWER parameter in INSTRUMENT PANEL MODULE data list. If scan tool indicates COMMAND BLOWER parameter is near zero percent, go to step 5. If scan tool indicates COMMAND BLOWER parameter is not near zero percent, go to next step.
- Use scan tool to perform, COMMAND BLOWER MOTOR OFF. Observe COMMANDED BLOWER parameter. If scan tool indicates COMMAND BLOWER parameter is near zero percent, go to step 7. If scan tool indicates COMMAND BLOWER parameter is not near zero percent, go to step 8.
- Disconnect IPM. If Blower Motor continues to operate, go to next step. If Blower Motor does not continue to operate, go to step 8.
- Inspect Blower Motor Control Processor harness connectors for loose wires and/or poor connections. If poor connection is found, repair as necessary. Go to step 12. If poor connection is not found, go to step 9.
- Inspect HVAC Control Module harness connectors for loose wires and/or poor connections. If poor connection is found, repair as necessary. Go to step 12. If poor connection is found, go to step 10.
- Check for loose wires and/or poor connections to Instrument Panel Module (IPM) harness connector. If poor connection is found, repair as necessary. Go to step 12. If poor connection is not found, go to step 11.
- Replace Blower Motor Control Processor. See BLOWER MOTOR CONTROL PROCESSOR under REMOVAL & INSTALLATION. Go to step 12.
- Replace HVAC Control Module. See HVAC CONTROL MODULE under REMOVAL & INSTALLATION. Go to step 12.
- Replace IPM. See INSTRUMENT PANEL MODULE (IPM) under REMOVAL & INSTALLATION. Go to step 12.
- Operate system to verify repair. If condition is corrected, system is okay. If condition is not corrected, go to step 2.
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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.