2014-2018 Cadillac CTS Brake Noise: Squeal, Grinding and Pulsation Causes

By Core Brake Parts Tech Team — Circleville, OH warehouse

Most brake noise on a 2014-2018 Cadillac CTS falls into three buckets: a short squeal on the first few stops after the car has sat, which GM documented in a service bulletin and fixes with copper paste on the pad ends; grinding, which almost always means pads worn to metal; and a pulsing pedal, which is disc thickness variation in the rotors. Identify which one you have before buying parts, because only two of the three need new brakes.

How the brakes work on the 2014-2018 CTS

This generation CTS uses four-wheel disc brakes with a vacuum power booster. The rear brakes are also the parking brake: the 2016 owner's manual describes an Electric Parking Brake (EPB) operated by a switch on the instrument panel to the left of the steering wheel, with a red status light and an amber warning light. There is no pedal or handle. That matters for service, because the rear calipers are motor-actuated for parking and have to be serviced with the factory procedure rather than simply pushed back with a clamp.

GM's own bulletins group the CTS with other rear-drive GM performance cars (ATS, CT6, Camaro, Corvette, SS), which is why the same noise fixes show up across all of them.

Squeal on the first few stops: GM bulletin 17-NA-040

If your CTS squeals or squeaks from the front brakes only on the first stops of the day, you are describing GM technical service bulletin 17-NA-040 almost word for word. The bulletin covers the 2014-2019 CTS (VIN A) along with the ATS, XTS, CT6 and others, and describes the condition this way:

• The noise normally only occurs on initial brake applications after the vehicle has sat for an extended time.
• It happens under light braking at speeds under 10 mph (16 km/h).
• After 1 to 6 brake applies, or after braking at higher speeds, the noise goes away.
• It may occur more often in high humidity.

The correction is not new pads. GM's procedure is to remove the pads, clean both ends of the abutment area on the pads and caliper brackets, and apply roughly 0.10 g (0.0035 oz) of copper paste to each end of the pad backing plate abutments that contact the bracket, without letting it reach the friction material. The bulletin states plainly that the pads should not be replaced for this condition. It also warns that wheel cleaners and power washers aimed at the calipers can wash the paste off, so the noise may come back after an aggressive wash, and the paste should be reapplied any time the pads are removed or replaced.

Two more details from the bulletin are worth knowing if you do the job yourself: do not remove the silencers (shims) from the pads, and GM recommends Brembo GM OEM pads because aftermarket pads can change braking performance. If you go aftermarket, choose a quality pad that comes with shims and hardware, and still lubricate the abutments the way the bulletin shows.

Grinding: worn pads and damaged rotors

A grinding or scraping noise that is present on every stop, and gets louder as you press harder, is a different problem. The two common causes are:

• Pads worn to the backing plate. Once the friction material is gone, steel rubs on the rotor. The rotors are almost always scored at that point and should be replaced along with the pads.
• Debris or a rusted rotor edge. A stone caught between the dust shield and rotor makes a constant scrape even with the brakes released. A car that has sat for weeks may grind briefly while surface rust clears, then go quiet.

Pull the wheels and look. Check pad thickness at both ends of each pad, including the inner pad you cannot see through the wheel spokes, and run a fingernail across the rotor face. Deep grooves, a raised lip at the outer edge, or blue heat spots mean new rotors. If the pads are worn unevenly inner to outer, the caliper slides or pistons are not moving freely and should be addressed at the same time.

For a car that needs everything, a complete 2014-2018 Cadillac CTS front and rear brake kit puts new rotors and pads on all four corners in one order. You can also shop brake pads and brake rotors separately if only one axle is worn.

Pulsation: disc thickness variation, not warped rotors

A pedal that pulses or a steering wheel that shakes when you brake from highway speed is usually blamed on warped rotors. Brake makers describe the real cause differently. Wagner's technical guidance explains that pulsation comes from disc thickness variation (DTV): as the thicker and thinner sections of the rotor pass through the caliper, the brake fluid rises and falls and you feel it in the pedal. The root cause is usually lateral runout, meaning the rotor wobbles slightly as it turns. Most vehicles call for lateral runout of two thousandths of an inch or less, and Wagner notes that even a small piece of rust between the hub and rotor can push it out of spec.

Over thousands of miles, that wobble makes the pad either wear the rotor thin at the high spot (semi-metallic pads) or build up material there (ceramic pads). Power Stop's guidance separates the two cases: pad material deposits show as visible smearing on the rotor face and the vibration gets worse when the brakes are hot, while true DTV is measured with a micrometer. Power Stop recommends measuring at a minimum of 6 points around the rotor and treats variation beyond .001 inch (0.025 mm) as not acceptable.

A hard pedal with an air noise: GM bulletin 17-NA-021

One noise is not a pad or rotor problem at all. GM bulletin 17-NA-021 covers the 2016-2018 CTS with the 3.6L engine (RPO LGX) for a hard brake pedal and/or an air type noise when the brakes are applied. GM's stated cause is oil in the brake booster. The correction is to inspect the booster vacuum hose assembly and sensor and the booster for oil; if oil is found, the hose assembly, booster and engine oil pump are replaced. The bulletin lists 12.7 hours of labor for the CTS, so this is a dealer or experienced shop job, and it is worth asking whether your car is still covered, since the bulletin references Powertrain coverage.

If you hear a hiss and the pedal suddenly takes much more effort, do not keep driving it as normal. Reduced assist means longer stops.

What to replace at the same time, and how hard the job is

Replacing pads and rotors on the CTS is a moderate job for a home mechanic with a torque wrench. The front is straightforward. The rear takes more care because of the Electric Parking Brake: follow the factory service manual procedure to put the EPB into its service position before retracting the rear pistons, and do not force them. While you are in there:

• Clean the hub faces to bare metal before installing rotors to keep runout down.
• Replace pad clips and hardware, and lubricate the pad abutments as GM's bulletin describes. A brake hardware kit is inexpensive insurance against noise returning.
• Check caliper slide pins for free movement and inspect the flexible hoses. Swollen or cracked brake hoses should be replaced.
• Torque the wheel lug nuts to the value in the owner's manual in a star pattern; uneven lug torque is a common source of runout.
• Bed in the new pads per the pad maker's instructions before any hard stops.

Frequently Asked Questions

Why do my CTS brakes squeal only in the morning?

That matches GM bulletin 17-NA-040: squeal on the first 1 to 6 light stops after the car has sat, often worse in humidity. The fix is cleaning the pad abutments and applying copper paste, not replacing the pads.

Are warped rotors causing my steering wheel to shake?

Usually the rotor has uneven thickness rather than a true warp. That variation typically starts with lateral runout from rust on the hub face or uneven lug torque. New rotors on a cleaned hub, torqued correctly, fix it.

Can I just replace the front pads if the front is grinding?

If you hear grinding, the pads have almost certainly worn into the rotors. Replace the rotors along with the pads, or the new pads will wear quickly and the noise may continue.

Do I need a scan tool to do the rear brakes on a CTS?

The rear calipers work with the Electric Parking Brake, so use the procedure in the factory service manual to put the EPB in its service position before retracting the pistons. Forcing them back can damage the caliper.

Is a hard brake pedal on a 2016-2018 CTS dangerous?

A hard pedal means reduced power assist and longer stopping distances. On 3.6L cars GM has a bulletin for oil in the brake booster, so have it diagnosed promptly rather than driving on it.

Sources

1. GM Service Bulletin 17-NA-040 (via NHTSA) - initial-apply squeal condition, 2014-2019 CTS coverage, copper paste procedure, do not replace pads
2. GM Service Bulletin 17-NA-021 (via NHTSA) - hard pedal and air noise from oil in the booster, 2016-2018 CTS 3.6L, 12.7 hr labor
3. Wagner Brake: Brake Pedal Pulsation and Disc Thickness Variation - DTV mechanism, runout spec, hub rust as cause
4. Power Stop: Why Do I Have a Pulsing Brake Pedal? - deposits vs DTV, 6-point measurement, .001 inch limit
5. 2016 Cadillac CTS Owner's Manual, Electric Parking Brake - EPB switch location and warning lights