Chassis, generic

C0503 Left Front Wheel Speed Sensor A Circuit High

Check engine lightOn
EmissionsNot relevant
Drive cycleNot required
Limp modePossible

With C0503 the left front circuit reads above its permitted level, which in practice means the signal wire is in contact with battery voltage. GM's 2016 hybrid tables set it when the signal line exceeds 12 V for 0.12 s; the 2023 tables look at current instead and react above 50 mA, many times what a healthy active sensor draws. Both rate it Type A, with a MIL on the first trip. GM also names C05A4, a low common sensor supply, among the codes that block C0503, so a supply fault should be dealt with first. Mitsubishi assigns C1061-12, a short in the front left sensor circuit, to C0503, detected within 1 s, check-engine lamp after one trip. Look for a harness pressed against a live feed or a sensor with an internal short.

Likely causes

Signal wire shorted to a battery-voltage feed
Internal short in the left front sensor
Sensor input stage in the ABS module defective

Symptoms

  • ABS and ESC warnings directly after switching on
  • Check-engine lamp on some makes (GM Type A, Mitsubishi)
  • Brake assist and hill descent control switched off

Repair estimate

DifficultyMediumDIY possible
Parts and labour€30–450
Time0.5–2.5 h

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

Parts involved

wss lfsensor wiring

Related codes

C0500C0501C0502C0504C0509C05A4

References: gsi.ext.gm.com, gsi.ext.gm.com, mitsubishitechinfo.com.