C1046

Code

ALFA ROMEO C — Chassis

Left rear wheel speed sensor

Brand: ALFA ROMEO

Type: C — Chassis

Views: UK: 6 EN: 12 RU: 8

AI status

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Page language: EN

Causes

Failed/shorted/open left rear wheel speed sensor
Damaged or corroded sensor connector or wiring harness (open, short to ground/power, high resistance)
Damaged or missing tone ring/reluctor on left rear hub or wheel bearing
Contamination (metal debris, heavy rust) on tone ring or sensor tip
Intermittent connector contact due to corrosion or bent terminals
Faulty ABS/ESP module or internal driver (less common)

Symptoms

ABS warning lamp illuminated (and/or traction/stability lamp)
ABS or traction control disabled or limited functionality
Intermittent ABS activation or unexpected ABS operation
ABS pump or solenoid faults during braking events
Cruise control or speed dependent systems may operate erratically
Stored freeze‑frame data or related wheel speed mismatch codes

What to check

Use scanner to read C1046 and any related codes; record freeze‑frame and live wheel speed data
Visually inspect left rear sensor, connector, wiring harness and tone ring for damage, debris or corrosion
Check for proper connector seating and bent/corroded pins; unplug and inspect connector contacts
Measure sensor resistance with multimeter (compare to spec if available)
Check continuity and for shorts to ground/power between sensor connector and ABS module connector
Backprobe sensor connector and spin wheel (or lift vehicle and run at low speed) to observe AC or digital signal with multimeter/oscilloscope

Signal parameters

Sensor type: either passive (variable reluctance) or active (Hall/VR with internal electronics) depending on vehicle variant
Passive (VR) expected: AC voltage that increases with wheel speed; at low rotation you may see ~0.1–2.0 VAC (value varies by model)
Active (Hall) expected: digital square wave or pulse referenced to supply (often 0–5 V or 0–12 V depending on design)
Typical DC resistance (passive sensors only): commonly on the order of hundreds to a few thousand ohms (spec varies by sensor)
Signal frequency: increases proportionally with wheel speed; wave should be consistent and symmetrical when viewed on an oscilloscope

Diagnostic algorithm

Read and record all ABS/traction codes and live wheel speed values using a capable scan tool. Note whether left rear shows no speed, erratic speed, or mismatch. 2) Perform a visual inspection of the left rear sensor, wiring, connector and tone ring. Remove debris and check for physical damage. 3) With ignition off, disconnect the left rear sensor connector; check pins for corrosion, bent pins or water ingress. Repair/clean connectors as needed. 4) Measure sensor DC resistance (if passive) and compare to spec. If open or shorted, replace sensor. 5) Check continuity from sensor connector to ABS module pin; check for shorts to ground/power. Repair any wiring faults. 6) With vehicle safely lifted and wheel free, backprobe sensor signal wire. Spin wheel by hand or briefly run wheel while monitoring AC voltage (VR) or digital pulses on an oscilloscope/scan tool. Look for consistent waveform without dropouts. 7) Inspect tone ring for missing teeth, heavy rust or metal debris; check bearing play. Replace tone ring or hub/bearing if damaged. 8) If wiring and sensor test good but problem persists, inspect ABS module connector for corrosion and verify module grounds and supply voltages. 9) After repairs, clear codes and perform road test with live data to confirm stable left rear wheel speed signal and no recurrence of C1046. 10) If intermittent and not repeatable, consider harness movement/wiggle testing while monitoring data to reproduce fault. Always document findings before replacing the ABS module.

Likely causes

Open or shorted sensor wiring between left rear wheel and ABS module
Failed left rear wheel speed sensor
Corroded/loose sensor connector at hub or ABS module
Damaged or missing tone ring or excessive play in wheel bearing causing erratic signal
Fault in ABS module input circuit (after wiring tests)

Fault status

⚠️ Status

Left rear wheel speed sensor circuit malfunction detected by ABS/traction control module (no or invalid signal from left rear wheel speed sensor).

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 0.5-2 hours

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