ABS Warning and Brake Calipers - Long Post

Question

Edited: I received photos from the shop and I’m wondering if this changes any opinions.

I have a 2016 Chevy Malibu LT 1.5L in Florida that we’ve had for going on 1.5 years. I’m sorry this is so lengthy.

I want to better understand and also confirm if the diagnosis we were given could be legitimate. I’m not a mechanic so to me it’s not making sense.

Our car has been running perfectly, no noises or any giveaways there was an issue. We went to leave in our car after using the car just an hour prior. When we reversed, there was a pulsating of the brakes which felt like the ABS had engaged. No warning lights appeared. We went forward and then back again to try and pinpoint what was going on.

We noticed it was only in reverse so we decided to go forward and see what would happen. After going only 100 ft max, we pressed the brakes normally to slow down but the car responded more like we had slammed on the brakes. There were still no warning lights on the dash. We took it back home where we parked it and left the car.

A few minutes after leaving I got a warning alert through the Chevy app that there was an issue with my ABS and something to the effect that if there were no warning lights I needed to take it to the shop. Two hours later we returned home. We decided to give it a better look and at this point our check engine light was on, no other warning lights.

After reading info we decided to pull the ABS fuses just to see if the problem still occurred. Mainly we hoped it wouldn’t so we could drive our car to the shop instead of towing it. The result was that other than the brakes feeling more stiff, for lack of a better word, the pulsating was gone. This was however a short experiment so we didn’t drive it extensively to really test it out.

Fast forward we decide to tow it to the shop and this is the diagnosis they gave.

• Replace Front Brakes and Rotors (that can’t be cut) due to heavy rust.
• Replace Rear Brakes and Rotors due to the heavy rust AND they assume the calipers locked up which is the pulsating we felt. The calipers etched (?) the rotors. So, Pads, rotors and calipers in the rear.
• They were able to see the ABS code that it threw but they aren’t entirely sure why and they thought perhaps because the calipers locked up it may have triggered the ABS code. I don’t know the exact code.

Now, they asked if we knew if the car came from up North, which we aren’t sure. That was the suggestion they gave as a possibility for the rust because it didn’t make sense to us. However, we’ve had our car in the shop on multiple occasions, the most recent being 5 months ago for tires.

If the rust is so bad the rotors can’t be saved wouldn’t the rust be noticed then? It isn’t sitting unused as it is our daily driver.

Also, can calipers lock up and not make noise? We never heard noise of any sort prior to this that would give away the idea that something was going wrong.

If the calipers locked up for the first time when we were reversing could they have done damage to the rotor in only a few presses of the brakes?

If the brakes and rotors are heavily rusted, wouldn’t we hear some of the tell tale noises that brake make under those circumstances?

Lastly, if it was the calipers and brakes causing the pulsating and odd hard brake stop why would the problem go away when the ABS fuses were pulled?

This is the Chevy dealer we’ve been taking our vehicle to and I want to feel comfortable with their diagnosis. Everything I’ve said here is what they’ve told us when we’ve tried to better understand it.

I have not been to the shop since they called this afternoon to visually see what they are seeing. I’m just trying to understand how all of this could actually line up because obviously I’m not a mechanic.

Answer 1

I'm having a silimar issue with my Toyota Yaris which I'm yet to fix, but I know for sure what is causing it: rust on the ABS sensor. Every wheel has an ABS sensor which reads the wheel speed. During braking, if one of the sensors read 0 and other sensors have a different reading, the wheel is skidding, so the brake pressure must be released a little. (This happens many times per second which you can feel and hear).

Now when rust builds up between the ABS wheel speed sensor and the ABS reluctor ring (see below image), this can cause the sensor to falsely read a wheel speed of 0.

(source: https://www.apecbraking.co.uk/Resources/TechniciansGuides/ABS-Sensors.aspx)

As for the origin of the car, in the north of America, the roads are salted in the winter which causes rust under the car, because salt splashes up to the car. That's probably why they asked you that.

Surface rust on the rotors cannot cause this behavior, because all rust is usually removed the first time you brake. Rotors can get rusty on the parts that are not touched by the brake pads (The outside and the inside that sits against the hub), but this cannot cause this behavior.

I'm not quite sure about the locking up calipers, but replacing all calipers and rotors seems a bit excessive to me if it may as well be caused by a bit of rust. Therefor the diagnosis they gave you doesn't make sense. Especially since the problems stopped when you pulled the ABS fuse.

Finally, the reason this issue will not throw an ABS warning light is because no ABS sensors are actually faulty. (They just sometimes read the wrong value due to rust, but there's no way of knowing this). The check engine light is unrelated to this issue.

Answer 2

Edit: Having seen the added pictures, I wouldn't call any of that "heavy rust". Brakes usually look a lot worse than that around here and still work fine. This is what heavy rust looks like. So the answer below may not be much good anymore. Your brakes may still need replacement but it might be worth getting a second opinion.

Orginal answer: The diagnostic seems plausible.

Calipers locking up is a common thing up North where we salt the roads. I've seen it happen on cars 3 years old. But the way it usually manifests itself is premature wear of the pads and discs, possibly with mild overheating. The usual fix is to replace the pads and discs, then clean and grease the caliper sliding pins. I suppose it's possible that mechanics in Florida would be unfamiliar with that procedure but that seems unlikely. Your calipers may well be rusted beyond repair.

I'm fairly certain calipers can't lock to the point of engaging ABS as you need a decent amount of pressure on the brakes for that. But Krijn's answer would cover that part of your problem. Which means they may need to eventually replace even more parts than what they've told you.

Now for such a new car, in Florida, to have more rust than we see in the North makes me suspect it has been flooded or at least driven through seawater. I don't have first hand experience with that but it's the most reasonable explanation I can think of.