ABS and Traction Control Lights Both On? It’s Probably a Wheel Speed Sensor
I get this one at least twice a week. Customer rolls in, dashboard lit up like a Christmas tree — ABS light, traction control light, sometimes the stability control light too. They’re worried the brakes are gonna fail. Nine times out of ten, it’s a wheel speed sensor.
Wheel speed sensors are simple little magnetic pickups. They sit right next to a toothed ring on each wheel hub and count how fast that wheel’s spinning. The ABS computer uses that info to keep your tires from locking up in a panic stop, and the traction control system uses it to cut wheel spin when you’re on ice or wet pavement. One sensor goes down, and the computer throws both lights on and shuts those systems off for safety. Your regular brakes still work — you just don’t have ABS or traction control until you fix it.
Thing is, you can’t just look at the dash and know which wheel. You need a scanner that reads ABS codes, not just engine codes. The cheap $30 Bluetooth dongles usually won’t cut it — those only talk to the engine computer. You need something that’ll pull chassis codes. Code comes back C0035, that’s your left front. C0040, right front. The last digit tells you which corner. Write it down and go after that wheel first.
Here’s the stuff that actually kills these sensors, in the order I see it in my bay.
What Goes Wrong
They Just Get Filthy
Road grime, brake dust, metal shavings from your rotors — all that crap ends up caked on the sensor face. The magnet can’t read through half an inch of crud, so it stops sending a clean signal. Sometimes you don’t even need a new sensor. I’ve fixed plenty just by pulling the old one, wiping the tip with a rag and some brake cleaner, and sticking it back in. Light goes off, customer’s happy, costs them nothing but labor.
The Wiring Harness Gets Chewed Up
The sensor wire runs from the wheel hub up through the fender liner and clips into a connector in the engine bay. On front wheels especially, that wire flexes every time you turn the steering wheel. After a decade of that, the copper strands inside the insulation start snapping. Sensor works fine driving straight, then the light pops on mid-turn. Or it’s intermittent — you hit a bump and the ABS light flickers. That’s almost always a wire, not the sensor itself.
Rust Jacks the Sensor Up
This one’s a Silverado classic. The sensor bolts to a machined pad on the steering knuckle. Over time, rust forms between the sensor bracket and the pad and literally pushes the sensor up and away from the tone ring. The computer sees a weak or missing signal at low speed, thinks the wheel’s locked, and starts pulsing the ABS on dry pavement when you’re barely moving. Scrape the rust off the mounting surface, bolt it back down, problem solved.
The Tone Ring Cracks
The tone ring is a notched metal ring pressed onto the CV axle or inside the wheel bearing. If it cracks or a tooth breaks off, the sensor reads a gap every time that spot comes around. You’ll feel the ABS chatter at parking lot speeds on dry ground. Tone ring replacement means pulling the axle or the hub, so the labor gets real. But before you go that far, check the sensor and the wiring first — those are way more common.
I had a Honda Odyssey in here a few months back, ABS would kick on every single time the guy slowed below 10 mph on his street. Drove me nuts for an hour. Turned out the tone ring on the right front CV axle had a hairline crack I couldn’t even see until I wire-brushed it clean. New axle, problem gone. But that’s the exception. Most of the time it’s the sensor.
Swapping One Out — The Right Way
Difficulty: Not bad if you’ve turned a wrench before. Maybe two hours for the first one, half that once you’ve done it.
What you need: Jack, jack stand, basic socket set (usually 8mm or 10mm, sometimes a 5mm Allen), flathead screwdriver, brake cleaner, anti-seize.
1. Scan It First
Don’t throw parts at it. Pull the code. Know which wheel before you lift anything.
2. Get the Wheel Off
Chock the opposite corner. Jack it up, put a stand under it, pull the wheel. Do not work under a car on just a jack.
3. Find the Sensor
Front wheels: sensor mounts on the steering knuckle, behind the brake rotor. Rear wheels: usually on the trailing arm or hub. Follow the black wire to make sure you’ve got the whole routing in your head before you start yanking on things.
4. Inspect Before You Remove
Trace the wire all the way up. Look for rub marks, cracked insulation, spots where the loom’s worn through. If the wire’s damaged, you’re replacing the whole assembly anyway. If it looks clean, unplug the connector and pop the wire out of the plastic clips along the fender liner.
5. Pull the Old Sensor
One bolt holds it in. Remove that. Now here’s where it gets fun — half the time the sensor’s rust-welded into the knuckle. Spray penetrating oil around it and let it sit five minutes. Grab the sensor body with pliers and twist it back and forth gently. Work it loose, don’t just reef on it. If you snap the plastic body off in the hole, you’re drilling it out and that ruins your afternoon.
6. Clean the Mounting Hole
Wire brush or emery cloth inside the hole where the sensor sits. Get the rust and gunk out. A clean seat means the new sensor sits at the right depth against the tone ring.
7. Install the New One
Light coat of anti-seize on the sensor body — not the tip. Slide it in, snug the bolt down to about 7-9 ft-lbs. That’s not much. Overtighten it and you’ll crack the plastic housing, then you’re buying another one. Route the new wire exactly like the old one, snap it into the clips, plug the connector.
8. Clear the Code and Drive
Clear the ABS codes with your scanner. Take it for a spin above 15 mph so the module can self-check and turn the lights off. If the light comes right back, you either got the wrong wheel or the tone ring’s the problem.
We carry a solid selection of ABS Wheel Speed Sensors if yours is toast.
What Breaks on What
Chevy Silverado / GMC Sierra (2007–2013): Rust jacking under the sensor bracket. ABS pulses at low speed on dry pavement. Scrape the mounting surface, reinstall, done. I’ve done this repair more times than I can count. GM should’ve put a stainless shim under that sensor from the factory.
Honda Accord (2003–2012): Rear sensor wires get beaten up by road debris and salt. The insulation cracks, water gets in, and the signal goes intermittent. You’ll get a permanent ABS light. Usually needs the whole sensor assembly.
Ford F-150 (2011–2018): Front sensor wires get pinched or stretched during strut replacements. If you just had front-end work done and now the ABS light’s on, check the sensor wire — a lot of shops zip-tie them back wrong and they rub on the CV axle boot.
You don’t need ABS for the brakes to stop the truck. But in a panic stop on wet pavement, it’s the difference between steering around the problem and sliding straight into it. A wheel speed sensor is a thirty-dollar part that keeps a safety system working. If both lights are on, scan it, figure out which corner, and fix it. It’s a Saturday morning job for most folks.
