ABS warning light on
Yellow ABS icon on dash — normal braking works fine, but anti-lock is disabled. How to diagnose via OBD-II.
When the ABS light is on, normal hydraulic braking still works. But ABS (and usually ESC/TCS too) is disabled — in a panic stop the wheels can lock. You can drive carefully, but don't delay diagnosis.
Most common cause: a bad wheel speed sensor (WSS). One of the four fails or has a wiring open. Next in line: the ABS module itself — pump or valve issues.
OBD-II: use Mode 03 or enhanced scan for ABS codes (C-codes, not P-codes). Look for C0035-C0050 (WSS) and C0110 (pump motor). Live WSS data can show which sensor reads zero or wrong speed.
First diagnostic steps
- Read ABS codes (needs a scanner with ABS module support)
- Check live WSS data on all 4 wheels while rolling at 15+ mph
- Inspect WSS connectors (corrosion, detachment)
- Inspect the tone ring on the suspected wheel (broken teeth, debris)
- Check power supply to the ABS module
Likely fault codes
Click a code for detailed description, causes, and diagnostic plan.