C003800 — Rear left wheel-speed sensor signal line short to ground or open; supply line open

Diagnostic algorithm

1. Read DTCs and live data with a capable scanner; note any other related codes.
2. Visually inspect the rear-left sensor, connector, wiring routing, and tone ring for obvious damage, contamination, or missing teeth.
3. Backprobe the sensor connector: with ignition ON, measure the sensor supply/reference voltage and ground presence. If supply is missing, trace supply wire and check fuses and ECU power output.
4. With connector disconnected, measure sensor resistance (for passive) or follow manufacturer procedure for active sensors. Compare to spec. An open or infinite reading indicates a failed sensor.
5. Check continuity between the sensor connector pins and the ABS module pins. Look for opens, high resistance, or short to ground. Repair any damaged wiring or connector pins.
6. If wiring checks good, reconnect and monitor live wheel-speed data while spinning the wheel (use lift or drive slowly). For passive sensors measure AC output while rotating. For active sensors check for proper digital waveform with oscilloscope or scan tool.
7. Perform a wiggle test on harness and connector while observing live-data to reveal intermittent faults.
8. If short-to-ground is present on signal line, isolate by disconnecting sections of harness or unplugging connectors until short is removed; repair insulation or replace wiring harness section as required.
9. After repairs or sensor replacement, clear DTCs and perform a test drive to verify the fault does not return and that wheel-speed readings are stable and consistent with other wheels.
10. If wiring and sensor are good but fault persists, consider testing or replacing ABS control module as a last step (follow manufacturer module replacement/calibration procedures).