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 4.3 W, STANDARDREPAIR AND DIAGNOSIS (SINGLE PAGE)BRAKESTRACTION CONTROLANTI-LOCK BRAKE SYSTEMDIAGNOSTIC TESTSDTC C0237: REAR SPEED SENSOR SIGNAL ERRATIC (GASOLINE ENGINES)DIAGNOSIS
1999 GMC Forward Control 4.3 W, Standard
DTC C0237: Rear Speed Sensor Signal Erratic (Gasoline Engines): Diagnosis
1999 GMC Forward Control 4.3 W, StandardSECTION Diagnosis
- Perform diagnostic system check. See DIAGNOSTIC SYSTEM CHECK. After performing diagnostic system check, go to next step.
- Turn ignition off. Disconnect 10-pin EBCM harness connector. Turn ignition switch to RUN position. Check voltage between 10-pin EBCM harness connector terminal "E" and ground. If voltage is greater than 10 volts, go to step 4) . If not, go to next step.
- Turn ignition off. Disconnect VCM harness connector C1. Check resistance between 10-pin EBCM harness connector terminal "E" and VCM harness connector terminal No. 15 (VSS signal output circuit). If resistance is 0-2 ohms, go to step 5) . If not, go to step 8) .
- Turn ignition off. Reconnect VCM harness connector. Turn ignition switch to RUN position. Using scan tool, clear DTCs. Test drive vehicle at speed greater than 15 MPH. Check for DTCs. If DTC C0237 resets, go to step 6) . If DTC does not reset, go to step 7) .
- Check resistance between 10-pin EBCM harness connector terminal "E" and ground. If resistance is infinite, check VSS. If resistance is not infinite, go to step 9) .
- Replace EBCM.
- Malfunction is intermittent. Inspect all connectors and harnesses for damage which may result in high resistance when all components are connected. See DIAGNOSTIC AIDS .
- Repair open in VSS signal circuit between EBCM and VCM.
- Repair short to ground in VSS signal circuit.
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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.