C0440

Code

Generic C — Chassis

Wheel Speed Sensor Input Circuit Fault

Brand: Generic

Type: C — Chassis

Views: UK: 18 EN: 39 RU: 15

AI status

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Page language: EN

Causes

Damaged or contaminated wheel speed (ABS) sensor
Broken or corroded wiring, pins, or connectors in the sensor harness
Reluctor (tone) ring damaged, missing teeth, or excessive air gap
Wheel bearing failure causing sensor misalignment or noise
Short to power or short to ground in sensor circuit
Poor ground or reference voltage at ABS/traction control module

Symptoms

ABS warning lamp illuminated
Traction control / ESC light on and functions disabled or limited
ABS may engage unexpectedly at low speeds or not engage under heavy braking
Speedometer or odometer erratic or inoperative (on some vehicles)
Cruise control disabled
Diagnostic trouble code(s) stored for wheel speed sensor circuit

What to check

Scan for stored codes and freeze frame data; confirm C0440 and note which wheel/sensor is affected if available
Visual inspection of suspect sensor, connector, and harness for damage, corrosion, or contamination
Check connector pins for bent/flattened contacts, corrosion, or water ingress
Wiggle test: with ignition on, gently move harness and connector while observing live sensor data for intermittency
Measure sensor supply/reference voltage and ground at the connector (back-probe) with key on
Measure sensor output signal while spinning the wheel (multimeter for AC sensors or oscilloscope for best results)

Signal parameters

Passive (magnetic) sensor: coil DC resistance commonly ~500–2000 ohms (varies by vehicle) — consult vehicle spec
Passive sensor output: AC voltage amplitude increases with wheel speed (may be a few hundred millivolts at low speeds to several volts at higher speed)
Active (hall/electronic) sensor: reference supply typically 5 V (sometimes 12 V) — supply should be stable within ±0.5 V of spec
Active sensor output: digital/pulse waveform typically 0–5 V (or 0.5–4.5 V) square wave referenced to ground
Frequency and amplitude are proportional to wheel speed; use an oscilloscope to verify clean, consistent waveform without dropouts or excessive noise
Consult the vehicle’s service manual for exact resistance, supply voltage, and waveform specifications for the specific sensor type

Diagnostic algorithm

Retrieve all ABS/traction codes and freeze frame using a capable scan tool; record affected wheel position if reported.
Perform a thorough visual inspection of the suspected wheel sensor, connector, and wiring for mechanical damage, corrosion, or contamination.
With ignition ON (engine OFF), back-probe the sensor connector: verify reference voltage (if active sensor), ground continuity, and check for intermittent signal while wiggling harness.
Measure sensor resistance (passive sensor) and compare to specification. Replace sensor if out of range.
Spin the wheel and monitor sensor output: use a multimeter (AC mode) for passive sensors or an oscilloscope for precise waveform analysis. Look for clean pulses and amplitude/frequency consistent with wheel speed.
Check continuity between sensor connector and ABS module pin to rule out harness opens or shorts; inspect and test ground circuits and grounds at the module.
Inspect the reluctor/tone wheel for missing/bent teeth, excessive runout, or large sensor-to-ring air gap; repair or replace as necessary.
If wiring and sensor check OK, test/inspect ABS module connectors and grounds. If module driver is suspected (no infection to good sensor), consider module bench testing or replacement per manufacturer guidance.
If diagnosis is intermittent, use extended live-data logging or road test with scan tool to capture failure conditions. Avoid replacing the ABS module until sensor/harness and connectors are proven good.
After repair, clear codes and perform a test drive to confirm the fault does not return.

Likely causes

Connector corrosion or loose pin at wheel sensor
Damaged sensor harness (chafed, pinched, broken wires) near suspension/steering knuckle
Contaminated or damaged sensor face or reluctor ring (missing/bent teeth)
Faulty wheel speed sensor (common on vehicles with high mileage)

Fault status

⚠️ Status

Wheel Speed Sensor Input Circuit Fault — the ABS/traction control module is detecting an invalid or missing signal from a wheel speed sensor circuit (open, short, intermittent, or implausible waveform). This prevents the system from reliably determining wheel speed for ABS/traction control functions.

🟡 Repair difficulty: Medium

⏱️ Diagnostic time: 1-3 hours