C1191
Speed Wheel Sensor LF Input Short Circuit To Ground
Chassis Chassis/Safety ABS wheel 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 is sending a constant ground signal instead of the normal variable signal it should produce. Think of it like a light switch stuck in the 'on' position instead of flickering on and off as it should.

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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
Vehicle may not stop smoothly or ABS fails to engage during braking
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors voltage changes from the left front wheel speed sensor as the wheel rotates. A properly functioning sensor produces an AC signal that toggles between high and low voltage. When shorted to ground, the sensor voltage remains stuck at 0V or near-ground potential, preventing the ECU from detecting wheel rotation.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Sensor Output Voltage 0.3V to 3.5V (alternating AC signal) Continuously below 0.2V (shorted to ground)
Signal Frequency 10-100 Hz (varies with wheel speed) No frequency detected or flat line
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Sensor wiring harness connector
Inspect the connector at the left front wheel for corrosion, moisture, or loose pins and clean or reseat as needed.
2
Wheel speed sensor wiring and routing
Check the sensor wire from wheel to ABS module for cracks, pinches, or exposed insulation that may contact the vehicle chassis.
3
Left front wheel speed sensor
Replace the sensor if wiring and connectors are intact, as internal coil failure or ceramic core damage causes permanent short to ground.