C0503Left Front Wheel Speed Sensor A Circuit High
- Generic OBD-II code · Chassis
- Turns on the check-engine light
- Can trigger limp mode
- How the car detects it
- 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.
- What you may notice
- 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
- Likely causes
- LikelySignal wire shorted to a battery-voltage feed
- PossibleInternal short in the left front sensor
- RareSensor input stage in the ABS module defective
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €450
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.