Code
C1045
ALFA ROMEO
C — Chassis
Left rear wheel speed sensor
Views:
UK: 11
EN: 15
RU: 10
AI status
Completed
Completed
100%
Causes
- Damaged or contaminated left rear wheel speed sensor
- Broken, shorted or corroded wiring/connector between sensor and ABS control module
- Damaged or missing tone ring/reluctor on the left rear hub
- Air gap too large (sensor-to-ring distance) or misalignment
- Faulty ABS/traction control module or internal connector fault
- Intermittent ground or power supply fault to the sensor
Symptoms
- ABS warning lamp and/or traction control (ESP) light illuminated
- Stability/traction control functions disabled or reduced
- ABS may activate incorrectly or not function under braking
- Possible speedometer or cruise control faults on some models
- Inconsistent or jittery brake feel under hard braking
What to check
- Retrieve freeze-frame and live data with a diagnostic scanner; observe left rear wheel speed value versus other wheels
- Visually inspect the left rear sensor, connector and tone ring for damage, contamination or missing teeth
- Check connector for corrosion, bent pins, water intrusion and proper locking
- Measure sensor supply, ground and signal at the harness connector with key ON (if active sensor)
- Measure sensor coil resistance (for passive/VR sensors) and compare to spec
- Back-probe the sensor while rotating the wheel and observe signal with a multimeter or oscilloscope
Signal parameters
- Passive (VR) sensor: AC voltage proportional to speed; typical coil resistance commonly ~500–2000 Ω (model dependent)
- Active (Hall/3‑wire) sensor: digital square wave referenced to vehicle supply (commonly ~5V or 12V) — check for pull‑up voltage
- At low speeds VR sensors produce small AC voltages (tens to hundreds mV); amplitude rises with speed
- Oscilloscope waveform should be clean sinusoidal (VR) or square pulse (Hall) with consistent frequency matching wheel speed
Diagnostic algorithm
- Connect scanner, confirm C1045 and note any other ABS/traction codes and freeze-frame data.
- Visually inspect the left rear sensor, harness routing, clips and tone ring. Repair obvious damage or contamination.
- Disconnect sensor connector, check for corrosion, bent pins and secure mating. Clean and apply dielectric grease if appropriate.
- Measure sensor resistance (for passive) or supply/pulse (for active) at the connector. Compare to factory spec.
- With wheel elevated, back-probe signal wire and spin the wheel. Use a scope or meter to confirm presence and quality of waveform.
- If no/poor signal at sensor connector but good signal at ABS module connector, inspect/repair wiring between them (continuity, short to ground/power).
- If wiring and connector are good but no proper signal, replace the left rear wheel speed sensor and retest.
- If new sensor still fails and wiring checks good, suspect ABS control module fault or internal connector issue; consult module-level diagnostics/service manual.
- Clear codes and perform a road test to confirm fault does not return.
Likely causes
- Corroded connector at the left rear sensor
- Sensor ruined by road debris, hub servicing or brake work
- Tone ring cracked, missing teeth, or covered in rust/metal shavings
- Wire rubbed through at suspension pivot or inside trunk wheelwell
- Moisture ingress into sensor or connector causing intermittent failure
Fault status
Status
Left rear wheel speed sensor malfunction detected — signal missing or out of expected range
Repair difficulty: Medium
Diagnostic time: 0.5-2.0 hours
Similar codes
Your experience will help others
+100 karma for a short comment :)
Was this AI description helpful?
Your feedback helps improve AI descriptions.
👍 Like
0
👎 Dislike
0
Send to email