C0804

Code

Generic C — Chassis

ABS Wheel Speed Sensor Circuit Fault

Brand: Generic

Type: C — Chassis

Views: UK: 5 EN: 17 RU: 8

AI status

Completed

ready

Completed 100%

Page language: EN

Causes

Damaged or broken sensor wiring harness
Corroded, loose or damaged connector at sensor or ABS module
Faulty wheel speed sensor (active or passive)
Damaged or missing tone ring/reluctor on wheel hub or ABS ring
Short to battery or ground in the sensor circuit
Intermittent contact from dirt, water ingress, or mechanical damage

Symptoms

ABS warning lamp illuminated (may be constant)
Traction/stability control light may also be on
Loss of ABS function during braking (ABS may be disabled)
Unresponsive or incorrect vehicle speed reading from affected wheel on scan tool
Intermittent faults or codes that appear after driving through water or rough roads

What to check

Read and record freeze frame and live data from ABS/traction module with a capable scan tool
Compare wheel speed readings for all four wheels at low speed — the faulty wheel will often show no or erratic speed
Visual inspection of sensor, connector, and wiring along the suspension/hub path for damage, corrosion, or pinched wiring
Inspect tone ring/reluctor on hub/axle for missing teeth, heavy rust or debris
Wiggle harness and connector while monitoring live data to check for intermittent changes
Check module grounds and battery voltage supply to ABS module

Signal parameters

Active (three‑wire/Hall) sensor: reference supply typically 5V (or vehicle specific), signal is a square/analog pulse ~0.5–4.5 V; signal frequency increases with wheel speed
Passive (two‑wire/magnetic) sensor: AC voltage that increases with speed; typical peak or peak‑to‑peak range ~0.1–8 V depending on speed and design
Typical passive sensor resistance (vehicle dependent): commonly in the hundreds to low thousands of ohms (e.g., ~800–2000 Ω) — consult OEM specs
Expected behavior: signal present and proportional to wheel speed; opposite wheel should show similar frequency/amplitude at equal speeds

Diagnostic algorithm

Confirm code and capture live wheel speed data with scan tool; note when the code sets (cold start, after water, during turning)
Perform a careful visual inspection of the suspect wheel sensor, connector, and wiring harness; repair obvious damage or corrosion
Backprobe sensor connector with ignition on (or engine running if required) and measure: reference voltage (if active sensor), signal waveform (oscilloscope preferred) or AC voltage (for passive sensors) while rotating the wheel slowly
Measure sensor resistance (with connector disconnected) and compare to OEM spec; check for open circuit or short to ground/battery
If live data shows no signal, wiggle the harness and connector to reproduce intermittent faults; repair chafed wiring or replace connector as required
Inspect tone ring for missing/bent teeth, heavy corrosion or mechanical contact; clean or replace tone ring/hub if damaged
If wiring and tone ring are good, replace the suspect wheel speed sensor and retest
After repair, clear codes and perform a test drive while monitoring live wheel speed data to confirm proper operation and absence of return codes
If problem persists and wiring checks out, consider ABS module input circuit tests or module replacement as a last step (consult OEM procedures)

Likely causes

Corroded sensor connector or pin(s) at wheel hub
Sensor wiring rubbed through or pinched near control arm or hub
Contaminated or damaged tone ring (missing teeth, heavy corrosion)
Failed wheel speed sensor due to heat, impact or water intrusion

Fault status

⚠️ Status

ABS control module detected a fault in the wheel speed sensor circuit (open/short/intermittent or implausible signal) for one wheel. ABS/traction functions may be limited until repaired.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours