C0504
Left Front Wheel Speed Sensor A Intermittent/Erratic
Intermittent or erratic signal from left-front wheel speed sensor A. Wheel-speed signals feed ABS, ESC, traction control, transmission and odometer — a single dropped signal disables all of these safety functions until repaired.
- Check engine light: Yes
- Emissions related: No
- Repair difficulty: medium
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
Common causes
Ordered by how often each turns out to be the cause.
- Connector loose or chafed wiringCommon
- Connector with intermittent contact under vibrationLess likely
- Harness routed against vibrating componentLess likely
Parts involved
- Wss Lf
- Sensor Wiring
C0504 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.