C0299

Code

Generic C — Chassis

Wheel Speed Sensor 'A' Circuit Intermittent

Brand: Generic

Type: C — Chassis

Views: UK: 12 EN: 13 RU: 12

AI status

Completed

ready

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Page language: EN

Causes

Damaged or chafed wiring harness to wheel speed sensor
Corroded, loose, or contaminated connector pins
Faulty wheel speed sensor (intermittent internal failure)
Damaged/missing/dirty tone ring or reluctor tooth
Intermittent short to power or ground in sensor circuit
Poor ground or reference voltage to sensor

Symptoms

ABS warning lamp and/or traction control warning lamp illuminated
Intermittent operation of ABS/ESC; unexpected ABS events or disabled ABS
Inconsistent speedometer reading (on some vehicles)
Hesitation of traction control or loss of stability control functions
Fault appears/disappears with steering/suspension movement or after hitting bumps
Freeze-frame shows occasional spikes, dropouts, or erratic wheel speed values

What to check

Retrieve freeze-frame and full DTC data with a scan tool; note which wheel is 'A' per service manual
Visually inspect sensor, connector, and wiring from sensor to the ABS/ECU for damage, corrosion, or pinch points
With key ON (engine off) observe live wheel speed data and wiggle harness/connector to reproduce dropouts
Inspect tone ring/reluctor for damage, missing teeth, heavy rust or debris and check sensor air gap
Backprobe connector and check reference supply and ground voltages per vehicle spec
Measure sensor resistance (for passive sensors) and compare to spec; for active sensors check supply voltage and output waveform

Signal parameters

Passive (magnetic) sensor: DC resistance typically ~300–2000 Ω (vehicle-specific); produces AC waveform whose amplitude increases with wheel speed (tens of mV to >1 Vpp)
Active (hall/active) sensor: reference supply commonly 5 V or 12 V; output is a square/pulsed signal 0–5 V (or 0–12 V) with frequency proportional to wheel speed
Typical frequency range: tens to several hundred Hz depending on vehicle speed and number of teeth on tone ring
Expected waveform characteristics: consistent pulse amplitude and spacing; no missing pulses, no excessive noise, no sudden dropouts
Check for stable reference voltage and solid ground at sensor connector per vehicle specification

Diagnostic algorithm

Connect an OBD-II scanner and record C0299 details, freeze-frame, and live wheel speed data
Clear the code and perform a short test drive to attempt to reproduce the fault while monitoring live data
Perform a visual inspection of the wheel sensor, connector, and wiring harness for damage, corrosion, or loose mounts
Inspect the tone ring/reluctor for missing teeth, cracks, heavy rust, or debris; clean or repair as needed
Backprobe the sensor connector: verify reference voltage and ground with key ON; note any intermittent loss while moving the harness or turning the steering
Measure sensor DC resistance (passive type) and compare to spec; if out of range replace sensor
Use an oscilloscope or good quality scope-equipped scan tool to observe waveform while wheel is rotated; look for irregularities (dropouts, noise, missing pulses)
Perform a wiggle test along the harness while monitoring live data or the oscilloscope to locate intermittent open/short
Check continuity and insulation resistance from sensor connector back to ABS module; look for short-to-power or short-to-ground
If wiring and connectors check OK but problem persists, swap with a known-good sensor or install a replacement sensor and retest
After repairs clear codes and verify through a road test and additional drive cycles to ensure fault does not return
If intermittent evidence points to the ABS/BCM module input, consult manufacturer service information for module bench tests or module replacement procedures

Likely causes

Broken or intermittent wire at the sensor pigtail/connector
Connector corrosion or bent/broken pins at wheel or harness splice
Contaminated sensor surface (metal slag, debris, brake dust) changing signal
Cracked or missing tone ring tooth or excessive rust on tone ring
Loose sensor mounting allowing movement and variable air gap
Intermittent short where harness rubs on chassis or suspension

Fault status

⚠️ Status

C0299 — Wheel Speed Sensor 'A' Circuit Intermittent detected. The controller has seen unstable or interrupted signals from the wheel speed sensor 'A'. Inspect sensor, tone ring, wiring and connectors for intermittent faults before replacing components.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2 hours