Code
C1042
ALFA ROMEO
C — Chassis
Right front wheel speed sensor
Views:
UK: 27
EN: 41
RU: 34
AI status
Completed
Completed
100%
Causes
- Damaged or failed right front wheel speed sensor
- Open, shorted, corroded or disconnected sensor connector or wiring
- Damaged or contaminated tone ring (reluctor) or missing teeth
- Incorrect sensor air gap or misalignment
- Intermittent connection due to movement or corrosion
- Faulty ABS/traction control module or internal driver fault
Symptoms
- ABS, traction control or stability warning lamp illuminated
- Reduced ABS or traction system functionality
- Inconsistent or frozen speed reading for right front wheel in scan tool data
- Brake pulsation or unusual noises near the wheel (if tone ring damaged)
- Possible intermittent loss of ABS until vehicle restarted or speed changes
What to check
- Read and record freeze frame and live data with a compatible scan tool (wheel speed values and fault history)
- Visually inspect right front sensor, wiring, connector and tone ring for damage, contamination or missing pieces
- Check for corrosion, bent pins or moisture in the sensor connector and at the ABS module harness
- Backprobe connector to observe raw sensor signal with a scope or multimeter (where applicable)
- Wiggle-test harness while monitoring live data to detect intermittent faults
- Compare right front wheel speed reading to other wheels while driving slowly
Signal parameters
- Passive (magnetic) sensor: AC waveform; amplitude increases with wheel speed. Expect small AC volts at low speed, rising with speed
- Active (hall/effect) sensor: DC-referenced pulse/square waveform (typically 0.5–4.5 V or 0–5 V depending on design) with frequency proportional to wheel speed
- At rest: wheel speed signal should be steady (0 V/0 Hz for passive or stable idle voltage for active)
- During rotation: clean repeating waveform, no missing pulses; frequency increases smoothly with wheel speed
- If using CAN/CAN-FD: wheel speed message for right front should update at the expected rate and track other wheel speeds logically
Diagnostic algorithm
- Retrieve all ABS/traction and related codes; note whether C1042 is current or intermittent and record freeze-frame/live data.
- Visually inspect right front sensor, connector, wiring harness and tone ring for mechanical damage, contamination or missing teeth.
- Clean connector and terminals, then reconnect. Clear codes and perform a short road test while monitoring live wheel speed data.
- Backprobe the sensor connector. For passive sensors check for AC voltage while wheel is rotated; for active sensors check for pulsed DC. Use an oscilloscope if available to confirm waveform shape and integrity.
- Check sensor resistance and continuity to the ABS module; inspect for short to ground or to battery. Compare to factory specification or a known-good sensor.
- Perform a wiggle/strain test on the harness and connector while observing live data to locate intermittent faults.
- If wiring and connector are good but signal is absent or abnormal, remove and bench-test or replace the sensor with a known-good unit.
- Inspect and repair or replace damaged tone ring or wheel hub if missing/chipped teeth or excessive rust/metal build-up is found.
- After repairs, clear codes and confirm proper operation with a thorough test drive and re-check live wheel speed values at various speeds.
- If problem persists and wiring and sensor are confirmed good, suspect ABS module input/driver fault and perform module-level diagnostics per factory procedure.
Likely causes
- Connector corrosion or loose terminal at the right front sensor
- Broken/chafed wiring harness to the right front hub
- Failed sensor element (open circuit or no output)
- Damaged tone ring (cracked, dirty or missing teeth)
- Sensor gap incorrect after recent suspension or brake work
Fault status
Status
Right front wheel speed sensor circuit — signal missing, implausible or out of range; ABS/traction control warning may be active.
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
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