C1155
Speed Wheel Sensor LF Input Circuit Failure
Chassis Chassis/Safety ABS wheel speed sensor 🔴 Serious — Stop or limit driving
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What This Actually Means
In plain language — no jargon

The left-front wheel speed sensor isn't sending proper signals to the brake control module, like a speedometer that suddenly stops working. Without this signal, the ABS and traction control systems can't function correctly.

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Symptoms You May Notice
3 known symptoms for this code
ABS warning light illuminated on dashboard
Traction control disabled or inoperative
Reduced braking performance or pulsing brake pedal
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the AC voltage signal from the LF wheel speed sensor as the wheel rotates. It expects a frequency proportional to wheel speed with signal amplitude between 0.2-2.0 volts. If the signal drops below minimum threshold, frequency is absent, or circuit resistance is out of range, a fault is triggered.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Sensor Signal Voltage 0.2 - 2.0 VAC Below 0.1 VAC or open circuit
Signal Frequency Proportional to wheel rotation No signal or erratic pulses
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Wheel speed sensor connector
Inspect and clean the LF wheel sensor connector and pins for corrosion or loose contacts.
2
Wheel speed sensor wiring harness
Check the wiring from LF sensor to module for cuts, pinches, or water damage; repair or reroute as needed.
3
Left-front wheel speed sensor
Replace the sensor if voltage and resistance tests fail; sensor gap to reluctor ring should be 0.3-1.5mm.