01 S60 brake pedal randomly pushes back

Post by **gnalan** » 23 Nov 2022, 15:05

Recently my brake pedal has been pushing back on my foot, occasionally. It's not the constant pulsating that you get from the ABS when trying to stop on ice. I'm not really sure how to describe it other than it feels like someone is hitting the brake pedal with a hammer back into my foot. It'll do it once or twice while I'm pushing on the brake pedal, and then I hear what sounds like a hissing sound if I continue to press on the brake pedal. Any ideas what this would be? The ABS light isn't on, the master cylinder is full, I don't see any leaks anywhere, and there's no codes in VIDA. It still stops, but I'm afraid to drive it like it is. I've never had a car do anything like this before, so I don't know what is going on.

Any and all help would be appreciated.

Post by **br0dy519** » 23 Nov 2022, 18:10

It's almost like the reverse of what you would expect having air in the lines, which causes a spongy pedal. Hissing noise, is it possible the brake booster seal is gone (vacuum leak)?

I would probably start by attempting to bleed one of the brake lines. Definitely want to follow this one in case it ever happens to me though.

Post by **gnalan** » 23 Nov 2022, 18:24

Could it be a wheel sensor? Everything was fine until I got a screw in my right front tire and had it replaced with a new tire. I never had any problems before the new tire. Could the tire place have messed something up?

Post by **br0dy519** » 23 Nov 2022, 19:18

Actually, yes when I had bad tone rings, I got very intermittent but erratic brake control similar to above. You should see the anti-skid message and an ABS light though.

Post by **gnalan** » 23 Nov 2022, 19:56

It only does it at slow speeds, I think. I'm trying to remember if it was doing the same thing when I was driving 65mph last week and having to slow down for traffic.

No messages or codes, so I'm not sure what's going on with it. (I have it for sale in the classified section if anyone is interested.)

Post by **Krons** » 24 Nov 2022, 20:29

If safe for you to do, check the wheel speed sensors while driving with your VIDA. On my new to me 05 XC90 I had bad sensor, easy to diagnose on my scan tool.

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Post by **gnalan** » 10 Dec 2022, 20:31

I sold the car before I got to verify if it was a bad wheel sensor or something else going on.