ABS and Traction Control Light On: What It Means
When the ABS and traction control (or StabiliTrak) lights come on together, it almost always means the system has lost a trustworthy signal from one of the four wheel speed sensors. Your regular brakes still work normally, but the anti-lock, traction, and stability features are switched off until the fault is fixed. The single most common culprit is a damaged or dirty wheel speed sensor, often from a bad wheel bearing or metal debris on the tone ring.
Trouble codes you may see
If you scan the car, these are the OBD-II codes most often behind this symptom:
Common causes
- 1
Faulty or dirty wheel speed sensor
The most frequent cause. The sensor reads a toothed tone/reluctor ring at each wheel. Dirt, metal debris on the magnetic ring, or a failed sensor drops the signal, setting codes like C0035 (left front), C0040 (right front), C0045 (left rear), or C0050 (right rear).
- 2
Damaged sensor wiring or connector
Harness wires near the wheels and CV axles get rubbed, cracked, or corroded. Water intrusion at the connector or ABS module (EBCM) can knock out multiple circuits at once.
- 3
Worn wheel bearing
Excess bearing play widens the gap between the sensor and tone ring, weakening or losing the signal. Often paired with a humming or growling noise from that corner.
- 4
Damaged tone/reluctor ring
Chipped or rusted teeth on the ring (built into the bearing or axle on many cars) produce erratic readings the module rejects.
- 5
ABS module (EBCM) or relay fault
Internal failures or a bad pump-motor relay (e.g. C0265 on GM) can disable the whole system even with healthy sensors.
- 6
Low battery or charging voltage
Marginal system voltage can trip ABS/traction faults; the lights may clear after a battery or alternator fix.
What to do
You can drive carefully to a shop, but treat it as caution: your anti-lock braking, traction control, and stability assist are disabled, so allow extra stopping distance and avoid hard braking in rain, snow, or ice. Check that all tires are properly inflated and look for an obviously damaged sensor or wiring at the wheels. Have a shop pull the C-codes to pinpoint which wheel sensor or module is at fault before replacing parts.
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