Code
C1020
Generic
C — Chassis
Right Rear Wheel Speed Sensor Circuit Malfunction
Views:
UK: 1
EN: 4
RU: 3
AI status
Completed
Completed
100%
Causes
- Damaged or chafed wiring harness to right rear wheel speed sensor
- Corroded/loose connector or poor ground
- Failed wheel speed sensor (magnetic or Hall type)
- Damaged or missing tone/ring reluctor on wheel/hub
- Wheel bearing damage causing sensor misalignment
- Contaminated sensor (metal debris, heavy rust)
Symptoms
- ABS warning lamp illuminated
- Traction control and/or stability control warning lights illuminated
- Possible loss of ABS/traction control functionality
- Erratic or zero wheel speed reading for right rear on scan tool
- Pulsating brake feel or altered ABS operation during braking events
- Occasional false slip/stability interventions
What to check
- Read all stored and pending ABS/traction codes and freeze frame data with a scan tool
- Observe live wheel speed sensor data for all four wheels at low rolling speed
- Visually inspect right rear sensor, connector, wiring and tone ring for damage, corrosion or debris
- Check for play in wheel bearing and correct sensor air gap to reluctor/tone ring
- Wiggle harness and connector while watching live data to find intermittent faults
- Measure sensor resistance (for passive sensors) and supply/pull-up voltages (for active/Hall sensors) at the connector
Signal parameters
- Passive (magnetic) sensor: DC resistance often ~800–3,000 Ω (varies by vehicle). Produces AC voltage that increases with wheel speed (typical low-speed AC ~0.2–2.0 VAC).
- Active (Hall/active) sensor: requires reference supply (commonly 5V or 12V) and provides a digital square or pulse output (0–5V or 0–12V) at a frequency proportional to wheel speed.
- Typical pulse frequency: low speeds tens of Hz, rising with wheel RPM; exact values are vehicle-specific — compare to other wheel sensors.
- Expected behavior: stable, symmetrical waveform without dropouts or high noise; no open circuit (OL) on resistance check for passive sensors.
Diagnostic algorithm
- Connect a scan tool and record C1020 and any related codes; note freeze frame and live wheel speed values.
- Verify vehicle-specific sensor type (passive vs active) from service data before electrical tests.
- Perform a visual inspection of the right rear sensor, tone ring/reluctor and harness — repair obvious damage or contamination.
- With wheel supported and rotated, observe live sensor data. If the right rear shows zero or erratic pulses while others are normal, suspect sensor/hardware or wiring.
- For passive sensors: disconnect sensor and measure DC resistance at the sensor leads; compare to spec or the opposite wheel. Check for open/short to ground.
- For active sensors: verify reference voltage/pull-up at the sensor connector with key on; then backprobe signal while rotating wheel — expect digital pulses.
- Use an oscilloscope to verify waveform integrity (amplitude, symmetry, no dropouts).
- Perform a wiggle/rock test on harness and connector while observing live data to find intermittent faults.
- Inspect and measure continuity and resistance of wiring back to ABS module; check grounds and connector pins for corrosion or bent pins.
- If wiring and sensor test good, swap right rear sensor with an identical known-good sensor (or swap with left rear if same type) and see if fault follows the sensor.
- Repair or replace failed sensor, damaged wiring, corroded connector, or damaged tone ring as indicated. Repair grounds and module connectors if faulty.
- Clear codes and perform a test drive to confirm repair; re-scan to ensure C1020 does not return.
Likely causes
- Wiring harness damage or connector corrosion at right rear sensor
- Failed right rear wheel speed sensor
- Damaged or missing tone ring on right rear hub
- Ground or power feed problem to sensor
Fault status
Status
Right Rear Wheel Speed Sensor Circuit Malfunction detected. ABS/traction control may be disabled; the fault indicates an open/short/intermittent or invalid signal from the right rear wheel speed sensor circuit.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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