Chassis, generic

C0504 Left Front Wheel Speed Sensor A Intermittent/Erratic

Check engine lightOn

EmissionsNot relevant

Drive cycleRequired

Limp modePossible

C0504 points to a left front speed signal that jumps or produces far too many edges, not one that is missing. GM's 2016 hybrid brake module stores a time stamp for every sensor edge in a buffer and sets C0504 within 0.03 s when that buffer overflows; the 2023 tables apply the same idea to a DMA transfer unit receiving time stamps too often. For 2020 Chevrolet Silverado and GMC Sierra 2500/3500HD, GM preliminary information PIT5707 ties C0504 and its right-hand twin C050A to manufacturing debris on the reluctor ring: clean it without using a magnet, which may mean removing the hub bearing. Mitsubishi (C1061-38) checks the signal between 10 and 60 km/h, needs two trips for the MIL and lists the sensor rotor among the causes.

Likely causes

Metal debris or dirt on the reluctor ring (GM PIT5707)

Loose contact in the sensor plug or a wire breaking under movement

Damaged tone ring or encoder

Symptoms

ABS lamp and service stability message on the driver display
Fault comes and goes with road surface or steering angle

Repair estimate

DifficultyMediumDIY possible

Parts and labour€0–450

Time0.5–2 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

wss lftone ring lfsensor wiring

References: gsi.ext.gm.com, static.nhtsa.gov, mitsubishitechinfo.com.