Diagnostic Aids

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Aids
WARNING: This page does not describe the selected car, but rather 9 other vehicles, including the 1996 GMC Vandura Special, 1996 GMC Vandura, 1996 GMC Savana Special, 1996 GMC Savana Camper Special, and 1996 GMC Savana. However, it is still accessible from the selected car via links, so may be relevant.

An intermittent malfunction may be caused by poor connection, rubbed through wire insulation, or a wire broken inside the insulation.

If complaint is that the ABS warning light comes on during moist environmental changes (rain, snow, car wash), all wheel speed sensor circuit should be thoroughly inspected for signs of water intrusion. If DTC is not current, check DTCs and simulate the effects of water intrusion by spraying suspected area with 5 percent salt water solution (2 tsp. salt to 12 oz. water). Test drive vehicle over various road surfaces at speed greater than 15 MPH for at least 30 seconds. If DTC resets, replace suspected harness.

Resistance of wheel speed sensor will increase as sensor temperature increases. When inspecting wheel speed sensor, inspect sensor terminals and harness connector for corrosion and/or water intrusion. If there is evidence of corrosion or water intrusion, replace wheel speed sensor.

RENDER: 1.0x

NO RELATED

Recommended Tools & Savings

Use the Manual With the Right Hardware

Pair factory procedures with proven DIY tools so the instructions are easier to execute.

Affiliate disclosure: We may earn a commission at no extra cost to you.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • β€’ You smell fuel, burning insulation, or see smoke.
  • β€’ Brakes feel soft, pull hard to one side, or make grinding noises.
  • β€’ The engine overheats, stalls repeatedly, or misfires under load.
  • β€’ You are missing required tools, torque specs, or safe lifting equipment.
  • β€’ You are not confident in the next step or safety outcome.