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 MANUALSFORD1999MUSTANG GT, 2D CONVERTIBLE, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)BODY & FRAMEWINDOWSPOWER WINDOW SYSTEMSYSTEM TESTSTEST A: NO COMMUNICATION WITH GENERIC ELECTRONIC MODULE
1999 Ford Mustang GT, 2D Convertible, Standard
Test A: No Communication With Generic Electronic Module
1999 Ford Mustang GT, 2D Convertible, StandardSECTION Test A: No Communication With Generic Electronic Module
NOTE:
Before proceeding with this test ensure voltage exists at input side of fuse No. 39 (5-amp) in central junction box. Repair as necessary. See appropriate wiring diagram in POWER DISTRIBUTION article in WIRING DIAGRAMS.
- Turn ignition switch to LOCK position. Disconnect Generic Electronic Module (GEM) harness connector C291. Measure voltage at terminal No. 2 (White/Yellow wire) at GEM harness connector C291. See Fig 1 . If battery voltage exists, go to next step. If battery voltage does not exist, go to step 3 .
- Measure resistance between ground and terminal No. 4 (Black/White wire) at GEM harness connector C291. If resistance is 5 ohms or less, go to step 4 . If resistance is greater than 5 ohms, repair open in Black/White wire. See GROUND DISTRIBUTION article in WIRING DIAGRAMS.
- Remove fuse No. 39 (5-amp) from central junction box. Measure resistance in White/Yellow wire between terminal No. 2 at GEM harness connector C291 and output side of fuse No. 39. If resistance is 5 ohms or less, repair power distribution circuit as necessary. See appropriate wiring diagram in POWER DISTRIBUTION article in WIRING DIAGRAMS. If resistance is greater than 5 ohms, repair open in White/Yellow wire.
- Measure voltage at terminal No. 4 (Black/White wire) at GEM harness connector C291. If voltage exists, repair short to voltage in Black/White wire. If voltage does not exist, repair module communication concern. See MODULE COMMUNICATIONS NETWORK - MUSTANG 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.