06 S60 R non-responsive brake pedal at startup Topic is solved

Post by **erikv11** » 25 May 2018, 07:42

Like the title says. When the car is cold (though even on warm spring days) the brake pedal is stiff and the brakes don't engage, even if you press hard on the pedal. After a few minutes pedal travel and braking are fine. Problem is intermittent. It can be unnerving when backing out of the driveway and the neighbor across the alley parked a little close, given the S60's dismal turning radius.

My wife mostly drives the car so I have only started to look into this. As far as I can tell there is no extra noise like the pump coming on a lot. No codes showing in VIDA. I am guessing the car has some kind of vacuum leak in the brake system but would appreciate suggestions for how to track down the issue, thanks.

Post by **regent** » 25 May 2018, 07:58

You are guessing 100% right on the vac leak: I would think booster hose check valve stuck open or leaking booster.
Just after you turn the engine off, there should be sufficient vacuum in there for 1-2 brake applications - if all is well.

If you turn the car off and do not press the pedal, the vacuum should stay there overnight. If it does not - then you have to find the leak. Could be a pinhole in the hose or a faulty pump. (I have replaced the vacuum hose on my S60 n/a at around 10 years for good measure)

Post by **oragex** » 25 May 2018, 08:24

I'd look first the the booster switch, see if it looks broken. May as well try undoing the hoses at the switch (careful how you grab the switch as the cover may break), if there's vacuum inside the booster you will hear a strong hissing as the vacuum is released.

My guess goes with an issue with the master but it's just a guess, maybe it's simply locking from being really worn. Does the pedal slowly sink when keeping pressure on it for 10-15 seconds (engine running)?

Post by **abscate** » 25 May 2018, 08:51

I think the collective brain is on the money with this one - leak in the vacuum hose. I found mine chafed to the cords on the steel bracket on the rear of the cylinder head on my 1999.

Post by **mrbrian200** » 25 May 2018, 21:52

With a hard pedal at startup I'm thinking you should hear the vacuum pump running. It makes a whiney-buzzy noise.

I believe the basic functional test is to push on the brake pedal with key on (KPII) engine not running and you should hear the pump make it's little whirring noise for a second or two each time you press the brake pedal.

No brake boost on a cold start is sort of the hallmark of a non-working pump. I don't think it should take 'minutes' at idle to build enough vacuum in the system to operate the brakes normally - you also likely have an air leak somewhere (hoses, brake booster, or the pump can sometimes develop an internal air leak.

Post by **scot850** » 25 May 2018, 23:26

It is usually the booster switch that fails, and that can leave the pump running all the time until the pump also fails. We had to have the pump and switch replaced under warranty at around 60,000 miles.

It is worth checking the pipes as suggested, but I'd then start with the switch and pray it is that. The pumps are around $500 CDN and the switch about $100 CDN.

Neil.

Post by **oragex** » 26 May 2018, 05:04

mrbrian200 wrote: ↑25 May 2018, 21:52 No brake boost on a cold start is sort of the hallmark of a non-working pump. I don't think it should take 'minutes' at idle to build enough vacuum in the system to operate the brakes normally - you also likely have an air leak somewhere (hoses, brake booster, or the pump can sometimes develop an internal air leak.

I think it depends. The brake booster is known to start leaking at the seal near the pedal, causing loss of vacuum when parked which would indeed make the pedal stiff with the engine off and also start the pump when switching the key to Pos II - however this will only happen if the booster has a leak. If the booster is good, the pedal should be 'soft' in the morning before starting the engine and the pump should not engage whit the key in Pos II. In other words, if the pump does engage at all it's because there is a problem. The pump is a back up I believe, I even think some years didn't have it (not sure about this though).

Side note, the booster starts leaking slowly but enough to engage the pump - this can last for years causing the pump to wear out then as mentioned there may be no more boost at a cold start. Perhaps the original poster can check the booster at the seal near the pedal by tossing the grey dust boot, if the white plastic tube has black marks on it it means the seal is damaged

Post by **erikv11** » 26 May 2018, 07:20

Thanks much for the suggestions. I wrote this last night but forgot to post it, but I think mrbrian200 nailed it.

I inspected hoses and they *look* fine. Did not test them. I didn't check the booster yet. But I did started zeroing in on the vacuum brake pump (https://www.fcpeuro.com/products/volvo- ... a-31317445?) and switch (https://www.fcpeuro.com/products/volvo- ... o-31400693), maybe found something.

jimmy57 says with the key on and engine off, the pump should come on after a few brake pedal pumps (https://www.matthewsvolvosite.com/forum ... =9&t=65260). But I couldn't get it to come on at all, after a dozen pumps. Even when the car starts, the pump doesn't come on, based on I can't feel it doing anything if I hold the pump while someone else starts the car and pushes the pedal.

So it seems like either the switch is bad or the pump is bad (or both), is there a way to tell? Unplug the pump and give it 12V from a spare car battery? I think if the pump is bad I would replace both.

regent wrote: ↑25 May 2018, 07:58 ...
If you turn the car off and do not press the pedal, the vacuum should stay there overnight. If it does not - then you have to find the leak. Could be a pinhole in the hose or a faulty pump. (I have replaced the vacuum hose on my S60 n/a at around 10 years for good measure)

I also know the system loses vacuum within a couple hours so that the pedal is basically always hard at morning startup - I guess that would also fit with a bad pump (or a bad hose, check valve etc).

zjevik · Post by **zjevik** » 26 May 2018, 08:16

I would change the vacuum switch first, but the pump could go bad if it was overworked for a long time.

I was chasing a small vacuum leak in my 06 S60 for a few years now. The brakes would loose vacuum in 20 minutes after I shut the car. I even changed the brake booster a year ago and it didn't help. Last week my cruise went out and I had to change the brake pedal position sensor in the brake booster (I didn't change it with the brake booster a year ago). This helped and the system now holds vacuum for the whole night.

Post by **erikv11** » 26 May 2018, 08:19

oragex wrote: ↑26 May 2018, 05:04 ...

Side note, the booster starts leaking slowly but enough to engage the pump - this can last for years causing the pump to wear out then as mentioned there may be no more boost at a cold start. Perhaps the original poster can check the booster at the seal near the pedal by tossing the grey dust boot, if the white plastic tube has black marks on it it means the seal is damaged
...

So here is a video just taken of my car. Is the seal gone too, based on the whoosh sound and the black marks?