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 DIAGNOSIS (SINGLE PAGE)BRAKESTRACTION CONTROLANTI-LOCK BRAKE SYSTEMDIAGNOSTIC TESTSDTC C0238: WHEEL SPEED SIGNAL MALFUNCTIONDIAGNOSIS
1999 GMC Forward Control 5.7 R, Automatic
DTC C0238: Wheel Speed Signal Malfunction: Diagnosis
1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnosis
- Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK. After performing diagnostic system check, go to next step.
- Inspect vehicle tires for variation in tire size. If all 4 tires are the same, go to next step.
- Clear DTCs using scan tool. Test drive vehicle. While test driving vehicle, use DATA LIST function on scan tool to monitor wheel speeds. If scan tool indicates a faulty sensor, go to affected DTC test to diagnose problem. If scan tool does not indicate a faulty sensor, problem is intermittent.
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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.