C0378

Code

Generic C — Chassis

ABS wheel speed sensor circuit fault

Brand: Generic

Type: C — Chassis

Views: UK: 13 EN: 23 RU: 12

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Page language: EN

Causes

Open or short in wheel speed sensor wiring
Corroded or loose sensor connector
Faulty wheel speed sensor (Hall-effect or variable reluctor)
Damaged or missing tone ring/reluctor teeth
Metal debris or excessive air gap between sensor and tone ring
Intermittent contact caused by broken shielded cable or chafing

Symptoms

ABS warning lamp illuminated
Traction Control or ESC warning lights may also illuminate
Possible ABS inoperative or unavailable message
Cruise control or speed-dependent functions may be disabled
Pulsation or unusual braking feel during ABS activation (may be intermittent)
Stored freeze frame or live data showing no wheel speed or erratic wheel speed readings

What to check

Read and record ABS and related codes with a scan tool; note freeze frame and live wheel speed values
Visual inspection of sensor, connector, wiring harness routing, and tone ring/reluctor for damage or contamination
Wiggle test harness/connectors while watching live data for intermittent changes
Measure sensor resistance (if applicable) and compare to manufacturer specification
Measure AC or DC signal at the sensor while rotating the wheel (use oscilloscope if available)
Check continuity and for shorts between sensor signal and vehicle ground or power

Signal parameters

Variable reluctor (VR) sensor: low-speed AC output typically low mV to several hundred mV rising with speed; frequency increases with wheel speed. Expected: increasing AC voltage and frequency as wheel rotates.
Hall-effect/magnetic digital sensor: square wave output referenced to vehicle supply (commonly 0–5 V or switched to 12 V on some systems); output toggles with tone ring teeth.
Typical DC resistance (approximate): VR sensors often ~500–2000 ohms (varies by application) — consult OEM spec.
Open-circuit: infinite resistance; short-circuit: near 0 ohms. Any value far outside OEM range indicates sensor fault.
Waveform quality: clean periodic sine/AC (VR) or clean square wave (Hall) without dropout, chatter or excessive noise.

Diagnostic algorithm

Retrieve stored codes and live wheel speed sensor data using a capable scan tool. Identify which wheel is reported (if specified).
Perform a visual inspection of the sensor, tone ring, and harness. Look for damaged wires, corrosion, loose connectors, missing tone ring teeth, or heavy contamination.
With ignition ON (engine off) and connector unplugged, measure sensor resistance and compare to OEM spec. Note: not all sensors allow resistance check (refer to service manual).
Reconnect sensor. Backprobe the signal and reference/ground pins. Spin wheel by hand (or lift vehicle and rotate) and observe live voltage or waveform with multimeter (AC for VR) or oscilloscope. Look for a consistent waveform that varies with wheel speed.
Perform a wiggle/strain test on harness and connector while monitoring live data for intermittent changes indicating broken wires.
Check continuity from the sensor connector to the ABS module pins and for unintended shorts to ground or battery power. Repair any wiring faults found.
If wiring and connector are good but sensor output is missing or incorrect, replace the sensor and retest.
If a replacement sensor does not restore correct signal, inspect tone ring condition and sensor mounting gap; replace or repair as needed.
If sensor, wiring and tone ring are good but module still shows fault, check ABS module power/ground and communication lines. Consider module input circuit testing or consult manufacturer service info before module replacement.
After repair, clear codes, perform a test drive and re-scan to verify the fault does not return.