Chassis, generic

C051A Left Rear Wheel Speed Sensor - Mechanical

Check engine lightUsually off

EmissionsNot relevant

Drive cycleRequired

Limp modePossible

C051A names a mechanical fault at the left rear sensor. Like its siblings it is listed but not documented by any manufacturer, so the actual setting rule is unknown. At the rear axle the encoder sits in different places: inside the hub bearing seal on many cars, as HELLA describes for multipole rings, or on the axle shaft or hub of rigid axles. Ford special service messages show the rear-specific risks: on Ford's F-53 motorhome chassis of 2020, rear axle tone rings bent during hub and rotor installation, and on 2021–2022 F-150 trucks with a three-quarter floating axle, metal particles on axle tone rings and sensors set rear sensor codes until the axle tubes were cleaned. Those Ford cases were stored as C0037 and C0036, not as C051A.

Likely causes

Metal particles or rust on the rear encoder or sensor tip

Rear tone ring bent or cracked, often after hub or brake work

Left rear hub bearing worn, encoder seal damaged

Symptoms

ABS lamp, sometimes only under load or on rough roads
Rear wheel speed drops out or jitters in live data

Repair estimate

DifficultyMediumDIY possible

Parts and labour€0–600

Time0.5–4 h

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

Parts involved

wss lrtone ring lr

References: static.nhtsa.gov, static.nhtsa.gov, hella.com.