C0420

Code

Generic C — Chassis

Right Rear Wheel Speed Sensor Circuit

Brand: Generic

Type: C — Chassis

Views: UK: 4 EN: 12 RU: 6

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Page language: EN

Causes

Open or short in right rear wheel speed sensor wiring or connector
Corroded/loose connector or poor pin contact
Failed wheel speed sensor (passive VR or active Hall/IC type)
Damaged or missing tone/reluctor ring on the right rear hub/axle
Contaminant or metal shavings on sensor or reluctor ring
Wheel bearing failure causing sensor-to-ring air gap or alignment change

Symptoms

ABS and/or traction control warning lamp illuminated
Limited or disabled ABS/ESC/traction control features
Speedometer may be erratic or incorrect (on some vehicles)
Unexpected ABS activation/pulsation or poor braking feel during ABS operation
Diagnostic trouble code C0420 stored in ABS/ESC module

What to check

Scan ABS/ESC module: read stored codes, freeze frame and live data for all wheel speeds
Visually inspect right rear wheel area: sensor, wiring, connector, tone ring and hub/bearing for damage or contamination
Check connector for corrosion, bent pins, water intrusion and secure fit
Wiggle harness and connector while watching live data or test lamp to reproduce intermittent faults
Compare right rear wheel speed signal/value against other wheel speeds using a scan tool

Signal parameters

Passive (VR) sensor: generates AC voltage proportional to wheel speed. Typical idle/low speed output can be ~0.1–2.0 Vp-p and increases with speed (varies by vehicle). Resistance range often around several hundred to a few thousand ohms (manufacturer specific).
Active (Hall/LS/IC) sensor: uses a 5V reference and returns a square wave or frequency signal; signal typically 0–5 V with frequency proportional to wheel speed.
Air gap: typical sensor-to-reluctor gap commonly 0.5–3.0 mm (check vehicle spec). Values vary by vehicle — consult service data for exact parameters.

Diagnostic algorithm

Confirm code and context: record freeze frame, note when lamp came on, clear codes and perform a drive cycle to see if C0420 returns.
Visual inspection: examine right rear sensor, wiring, clips, boots, and tone ring for damage, contamination, bent teeth or missing pieces.
Connector check: disconnect sensor connector, inspect pins for corrosion, bent or pushed-back pins; clean and reassemble or repair as needed.
Resistance test (passive sensor): measure sensor resistance with multimeter and compare to specification. Abnormal open/short indicates sensor failure. (If active sensor, skip resistance test.)
Reference/power test (active sensor): with ignition on, check for reference voltage (commonly 5V) and ground at the sensor connector; if missing, trace supply/ground back to fuse/ABS module.
Signal output test: spin the wheel (jack and support vehicle safely) and measure AC voltage (passive) or signal waveform/frequency (active) with oscilloscope or multimeter capable of frequency/AC measurement while watching live data on a scan tool.
Continuity check: verify continuity and no short to ground/power between sensor connector and ABS module connector pins. Wiggle harness to check for intermittent faults.
Inspect reluctor/tone ring and wheel bearing: check for missing/broken teeth, heavy rust build-up, or bearing play that changes gap while rotating.
Swap test (if applicable and safe): swap right rear sensor with another known-good sensor from another wheel (when same type) and see if code follows the sensor. Only do if sensors are identical and swap is reversible.
Repair/replace: repair wiring/connector faults, clean or replace tone ring, replace sensor if failed. After repair, clear codes and perform road test to verify no return of C0420.
If wiring and sensor good but fault persists: check ABS module power/ground and module internal faults; consider module diagnostic/repair per manufacturer procedures.

Likely causes

Wiring harness damage at suspension articulation point or inside wheel well
Corroded connector at sensor or at junction to vehicle wiring
Sensor physically damaged by road debris or corrosion
Reluctor ring teeth damaged, bent or covered with rust/debris

Fault status

⚠️ Status

C0420 — Right Rear Wheel Speed Sensor Circuit: ABS/ESC reports an invalid or missing wheel speed signal for the right rear wheel. Investigate sensor, wiring, connector, and tone ring.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2.0 hours