2008-2016 Cadillac CTS ABS Light On: Common Causes and Fixes

By Core Brake Parts Tech Team — Circleville, OH warehouse

When the ABS light comes on in a 2008-2016 Cadillac CTS, the most common cause is a wheel speed sensor that has lost its signal, and on many of these cars the sensor itself is fine: GM traced a large share of these faults to metal debris stuck to the magnetic encoder ring on the wheel bearing hub. A scan tool that reads chassis (C) codes will tell you which corner is at fault, and the fix is often a cleaning job, not a new part.

Below is how the system works on the CTS, what the light and codes mean, the causes in the order a technician checks them, and when you actually need parts.

What the ABS Light Means on a CTS

According to the CTS owner manual, the ABS warning light should come on briefly when the engine starts. If it stays on, or comes on while driving, GM tells owners to stop when it is safe, turn the ignition off, and restart to reset the system. If the light stays on or returns, the car needs service.

The key point is what the other brake light is doing:

• ABS light on, red brake system light off: the manual states the vehicle still has brakes, but not antilock brakes. Normal braking works; the wheels can lock in a hard stop on a slick surface.
• ABS light and red brake system light both on: the manual states the car does not have antilock brakes and there is a problem with the regular brakes. Treat this as a stop-driving condition until it is checked.

The CTS Driver Information Center can also show SERVICE BRAKE ASSIST or SERVICE BRAKE SYSTEM. The manual ties SERVICE BRAKE SYSTEM to a low brake fluid level, so check the reservoir before anything else when that message appears.

How ABS Wheel Speed Sensing Works on This Car

The Electronic Brake Control Module (EBCM) watches the speed of all four wheels. On the CTS, each wheel speed sensor reads a magnetic encoder ring built into the wheel bearing hub assembly rather than a traditional toothed tone ring. GM's service bulletin describes this encoder as a magnetized rubber ring, typically brown, with many north and south pole pairs around its circumference. As it spins past the sensor, the sensor produces a signal that it converts into a digital square wave for the module.

The same wheel speed data feeds traction control and StabiliTrak. That is why an ABS fault on a CTS usually brings the traction control and StabiliTrak warnings on at the same time. It is one fault showing up in three systems, not three separate failures.

When ABS is working and actively intervening, the manual notes you may hear the ABS pump or motor running and feel the pedal pulsate. That is normal during a hard stop and is not a fault.

Reading the Codes: Which Corner Is Failing

A basic engine-code reader will not show ABS faults. You need a scan tool that reads the EBCM. GM's bulletin maps the four wheel speed sensor codes to specific corners:

GM's bulletin specifically flags these codes when they carry symptom bytes 18, 5A or 0F. If your scan tool shows the symptom byte, note it: those are the cases GM says are usually fixed by cleaning the encoder.

Common Causes, in the Order to Check Them

1. Metal debris on the magnetic encoder ring

GM Service Bulletin 17-NA-047 (which replaced earlier preliminary information PIC5428) lists the 2008-2014 CTS among the affected models. The cause: single or multiple pieces of ferrous metal debris stuck to the magnetic encoder ring on the inboard side of the bearing hub. Metal particles and rust scale are attracted to the magnet and distort the signal.

Symptoms GM lists besides the warning lights:

• A brief clicking, ratcheting, grinding or ABS pump noise at parking-lot speeds, heard from inside the car.
• A traction control or StabiliTrak light that flashes at low speed.

GM notes those last two can happen with no codes stored at all, which is why owners can be told nothing is wrong before the light eventually stays on. The bulletin covers CTS model years through 2014; on a 2015-2016 CTS the same inspection is still a sensible first step, but the bulletin itself does not list those years.

2. Damaged sensor wiring or connector

The sensor harness runs near the suspension and brakes, where it flexes with every bump and sits in road spray. A chafed wire or corroded connector produces the same codes as a failed sensor. Inspect the harness along its full length at the flagged corner before buying anything.

3. A failed wheel speed sensor

If the encoder is clean, the wiring is intact and the code returns, the sensor is the next suspect. A scan tool that shows live wheel speeds is the best check: drive slowly and watch for one wheel that drops out or reads erratically compared to the other three.

4. A worn or damaged wheel bearing hub

Because the encoder ring is part of the hub assembly, a torn encoder or a bearing with play means replacing the hub. If you hear a growl that changes with road speed or feel play when you rock the wheel, the bearing itself is the likely fault.

5. Low brake fluid or a hydraulic fault

If the red brake light or SERVICE BRAKE SYSTEM message is on with the ABS light, check the fluid level first. The manual explains that fluid drops naturally as pads wear, and that a low level otherwise means a leak. It also warns against simply topping off the reservoir, since adding fluid does not fix a leak.

The Fix: Cleaning the Encoder Ring

GM's bulletin says most of these repairs can be done without replacing the hub or the sensor, and its parts section for the concern states no parts are needed. The procedure, in summary:

1. Use the code to pick the corner (C0035 left front through C0050 right rear).
2. Inspect the encoder ring on the inboard side of that hub for debris. On some applications the hub has to come off to reach it properly.
3. Brush the debris off gently with a dry, soft nylon brush. If debris remains, wash the ring with a mild soap detergent and wipe it dry.
4. Clear the codes with a scan tool and verify the repair.

Two cautions from GM matter here: do not use a magnet or any magnetic tool to pick the debris off, because an outside magnet can damage the encoder; and be careful not to damage the bearing's outer seal while cleaning. GM also notes the bulletin does not apply to capped wheel bearings.

For scale, GM's warranty labor allowance for cleaning one side is 0.4 hour for a front corner on a rear-wheel-drive CTS and 1.0 hour for a front corner on an AWD CTS, with rear corners allowed 0.9 to 1.1 hours depending on the version. It is a moderate job, not a quick one, and reaching the inboard side generally means taking the brakes apart at that corner.

What to Replace While You Are In There

With the brakes at that corner already apart, it is the right time to measure what is there:

• Pads: check thickness on both inner and outer pads. The CTS manual states brake linings should always be replaced as complete axle sets, so if one side is low, do both. See our brake pads for your vehicle.
• Rotors: if the rotor is below minimum thickness, scored or causing pulsation, replace it now instead of taking the corner apart again later. Browse replacement brake rotors.
• Hub assembly: if the encoder ring is torn or the bearing has play, cleaning will not fix it. The hub is the part.
• Brake fluid: the CTS uses DOT 3 brake fluid from a new, sealed container, per the owner manual. GM warns that even a few drops of mineral-based oil such as engine oil can damage hydraulic parts badly enough that they must be replaced.

For performance CTS and CTS-V owners, we carry fitment-matched pads such as the EBC Redstuff front pads for the 2008-2013 CTS 3.6L and the Hawk HPS 5.0 front pads for the 2008-2014 CTS-V. Check the fitment notes on each listing, because brake size varies by trim. For everything else, start at our full brake parts catalog.

Is It Safe to Drive With the ABS Light On?

If only the ABS light (along with the traction and StabiliTrak lights) is on, the base brakes still work, according to GM's manual. What you lose is antilock control, traction control and stability control, which matters most in rain, snow and emergency stops. Drive gently, leave extra following distance, and get it diagnosed soon. If the red brake warning light is also on, or the pedal feels low or soft, do not keep driving it.

Frequently Asked Questions

Why are the ABS, traction control and StabiliTrak lights all on at once on my CTS?

All three systems rely on the same wheel speed signals. When the module loses one wheel's signal, the related warnings come on together. It is usually one fault at one corner.

Does code C0035 always mean a bad wheel speed sensor?

No. C0035 points to the left front corner, but GM found many cases were caused by debris on the hub's magnetic encoder ring. Inspect and clean the encoder and check the wiring before replacing the sensor.

Can I clean the encoder ring with a magnet?

No. GM specifically warns against using any magnetic tool, because an outside magnet can damage the encoder. Use a dry soft nylon brush, then mild soap and water if needed.

My CTS makes a clicking or grinding noise at low speed but there are no codes. Is that related?

It can be. GM's bulletin lists a brief click, ratchet, grind or ABS pump noise at parking-lot speeds, sometimes with no codes stored, as a symptom of encoder debris.

Will new brake pads turn off the ABS light?

Not by themselves. Pads have nothing to do with the wheel speed signal. Worn pads do lower the fluid level, though, so if the red brake light is also on, check pads and fluid during the same repair.

What brake fluid does the 2008-2016 Cadillac CTS use?

The CTS owner manual specifies DOT 3 brake fluid from a new, sealed container, as marked on the reservoir cap.

Sources

1. GM Service Bulletin 17-NA-047 (NHTSA) - CTS 2008-2014 coverage, encoder debris cause, symptoms, cleaning procedure, no parts required, capped-bearing exclusion, labor times
2. GM Preliminary Information PIC5428E (NHTSA) - C0035/C0040/C0045/C0050 corner mapping, symptom bytes 18, 5A, 0F, magnetic encoder design
3. 2012 Cadillac CTS/CTS-V Owner Manual - ABS and brake warning light behavior, DIC brake messages, ABS pump noise and pedal pulsation, DOT 3 fluid, axle-set pad replacement
4. Bosch Auto Parts - Wheel Speed Sensors - keep sensors clean of debris, ice, snow and dirt