[seminole_kev]

So, kind of hard to explain, but I'll do my best. Recently my 2013 XC70 has started exhibiting a weird braking behavior. Basically when braking normally, in the middle, it will decide to suddenly give it a boost of additional braking at an odd moment. Feels like a brake assist is kicking in prematurely/too hard. It isn't the transmission downshifting harshly as there's no change in RPM when it happens. It just makes a momentary jerk to the car as it brakes harder than it should. This is just driving around in "D" normally, not aggressively braking, and not in any manual mode shifting. Also, is in normal, dry weather. Not raining/snowing or anything traction related.

Not sure if an electronic safety system is doing something screwy, or what. It is momentary, so no pulsing nor anything that feels mechanical (like rotors). I'll need to end up taking it into the shop, but was curious if:

a) Anyone else has experienced anything like this?
b) If perhaps there was a TSB or recall related to something like this (just to hopefully save time at the dealership)?

Thoughts?

*Edit - Ok, had a chance to drive it around for a bit today, and it does actually seem to coincide with downshifts. And does seem to be getting worse. I'll be taking it in to an appointment later this week, but on that note, I'd guess it is actually something transmission related after all. This is a FWD model (not AWD), but not sure if there's any common/known problems with these automatic units.

 

[bigtimemcalpine]

Very strange. Have you checked the brake fluid level? Any warnings on the info screen? Have you had the brake vacuum pump seals replaced? I ask as it is very common for it to leak at about 80,000miles. I suppose that if it leaked enough it might cause a failure of the pump itself resulting in decreased performance.

Here is a link to a guide for this fix:

 

[seminole_kev]

Very strange. Have you checked the brake fluid level? Any warnings on the info screen? Have you had the brake vacuum pump seals replaced? I ask as it is very common for it to leak at about 80,000miles. I suppose that if it leaked enough it might cause a failure of the pump itself resulting in decreased performance.

Here is a link to a guide for this fix:

No warning lights/messages, and it isn't a loss of braking performance, but rather the opposite. A very quick surge in braking power (almost like one of the electronic nannies are stepping in for a second) and it isn't at any set pedal depth or time braking. The car only has ~20k miles, and I have a few months of warranty left I believe, so I'll have to take it in. Just that sometimes if someone already knows the issue, it can help speed up the dealer's troubleshooting time (especially if there's a TSB to point to).

 

[T5 for Life]

Almost sounds like over-sensitive or improperly triggered ABS, or something screwy with the City Safety/Collision Detection software, though with the latter you might get a warning on the dash (if your car has that feature).

What speed does this occur at? City Safety is only active below 19mph (or something around that)

 

[seminole_kev]

It is equipped with city safe, and is at relatively slow speeds (though I think in 2013 it can engage at something like 32 mph and below, vs the earlier 19, but I could be remembering incorrectly)

 

[Schmoyoho]

The only thing I can think of is that it feels like the lock-up in the transmission can be aggressive under some circumstances during braking. I think the newer cars are more tuned for fuel economy so it'll engage more than older cars even during braking to save some petrol. Sometimes I've felt that if I've held the brake pedal depressed constantly, the car has suddenly begun braking more or less. Actually a bit scary when it's less, at least the first times it happened.

 

[T5 for Life]

No change in RPM noted, schmoyho. Defintely sounds like it's "brake" related (ie: some system that actually used the brakes electronically) vs. drivetrain intervention.

 

[seminole_kev]

I've got an appointment this coming week to have it looked at. As long as they don't "Could Not Duplicate" it, I'll let you know what they find out. My gut says one of the electronic nannies is interfering (either by a code issue, or getting bum data from a sensor), but who knows.

 

[seminole_kev]

*Edit - Ok, had a chance to drive it around for a bit today, and it does actually seem to coincide with downshifts. And does seem to be getting worse. I'll be taking it in to an appointment later this week, but on that note, I'd guess it is actually something transmission related after all. This is a FWD model (not AWD), but not sure if there's any common/known problems with these automatic units.

 

[CrossingCountries]

*Edit - Ok, had a chance to drive it around for a bit today, and it does actually seem to coincide with downshifts. And does seem to be getting worse. I'll be taking it in to an appointment later this week, but on that note, I'd guess it is actually something transmission related after all. This is a FWD model (not AWD), but not sure if there's any common/known problems with these automatic units.

When does is it happen,...in slow traffic around town or when you brake slowly from lets say 60mph-to a full stop? I mean when it happens, does it happen at around 10/20mph coming from 60?? Have the feeling mine is doing something similar lately but at very low speed, approaching a stop light e.g.
Could be my imagination but at times it feels I am pushing an air-bubble away with my foot before it kicks in. Difficult to explain.

A malfunctioning ABS wheel speed sensor can cause abnormal braking behavior when braking at low speeds. A dirty sensor can have the same effect and can be "fixed" by cleaning the sensor and the sensor wheel.

Read this thread: http://www.volvoxc.com/forums/showthread.php?28732-Jerky-Brakes-on-used-XC70-2012

"Hello everybody, I tried searching around for this topic, but I didn't come up with anything. Hopefully I'm not duplicating another post.

I just purchased a used 2012 XC70 T5 with about 60k miles on it. I love the car, but I've noticed that when braking, especially at low speeds, something seems to clamp down midway through the deceleration. I know the this model has a braking assist option that accelerates the braking force when the brakes are applied rapidly, but that's not what's happening in my case.

I'll be doing about 25 mph and I'll go to gradually apply the brake pedal as I approach a stop light. A second or two later it's like the car is automatically slamming on the brakes. The car doesn't screech to a halt or anything, but there is a definite lurch and then a release.

Is this a known issue? Anyone else experienced this?

Thanks!

UPDATE: I'm not experiencing the jerk at highway speeds. Also, it seems that once the brakes heat up (15-20 minutes of driving) the condition pretty much goes away.
"A software update fixed the problem. I took the car to Volvo and they inspected the brakes and couldn't find anything wrong. Then the updated the software on the car and 'poof' the problem went away. The service guy said that he had seen issues like that before that were fixed with a software update"

 

[seminole_kev]

Thanks for putting that together, Crossing. It think I've only noticed it at low speed, particularly that final bit when you're close to stopping. Much like the last section of that topic you posted.

Also, it isn't that the braking becomes progressively stronger as the pedal is depressed (which would be non-linear, but predictably progressive), or a stair step increase even, but rather that there will be an unpredictable sudden jerk in the middle of breaking. It isn't a modern car thing, but something that is not behaving correctly. Though I do appreciate you putting the various articles together. Especially that last topic as that one sound very similar to me.

Honestly, as I have some trips up out to icy areas soon, I don't trust it as it is hard enough to potentially upset the balance of the car. I know the safety systems would potentially counter act that, but still. Hopefully something the dealer can a) duplicate and b) fix. I'll update what they find out in a few days.

 

[gorj]

I know I sound like a broken record in the forum, but have you changed the ATF? It could be a transmission issue. I suggest a change every 50k miles. Volvo claims it never needs changing, but that is bull hockey, especially since the Japanese, who build it, left out a filter!

 

[CrossingCountries]

There seems to be much discussion in the forums about changing the ATF on an XC70. My 2013 XC70 3.2 is just about to reach 50K miles. I have always tried to change the ATF in all my Volvo's about every 50K miles. So today I changed the ATF. The standard line from Volvo is the ATF is good for a lifetime. I consider that to be poor advice. There is much going on inside an automatic transmission with clutches, bands, drums, valves, gears, bearings, etc. and all of them are dependent on the quality of the ATF. As in any mechanical device there is friction that causes heat which over time tends to break down the lubricant of these devises. Also, due to the nature of the clutches and bands some of the their surface material finds its way into the lubricant. Thus it seems prudent to replace the lubricating media - the ATF. The drained ATF was dark, but had no brunt smell.

(...) You did the right thing...I did the same. I love preventive maintenance. Dont think its the problem in this case...

 

[seminole_kev]

gorj - good suggestion, but not even at 25k miles yet ;-)

 

[seminole_kev]

Welp, dealer Could Not Duplicate it, but did apply a software update to the transmission, which (at least initially) seems to have helped. Weirdly, when I picked it up, on the way home I noticed that the driver's one touch up/down function stopped working (still would go up/down while holding button), but after a couple of power cycles, that cleared up. Some weird byproduct of code updates I'd guess. Just a bit odd.

Anyway, looks like it is, at least initially, doing better after the software update to the transmission.

 

[CrossingCountries]

I think after a software update, the Geartronic needs to "reprogram" itself and adjusts itself as you go. Like a memory building up.

 

[T5 for Life]

The transmission does need to "learn". There's actually a process the dealer should have followed to re-calibrate the transmission before they gave it back to you. Do you know if they did that?

 

[tommar]

@semino

Welp, dealer Could Not Duplicate it, but did apply a software update to the transmission, which (at least initially) seems to have helped. Weirdly, when I picked it up, on the way home I noticed that the driver's one touch up/down function stopped working (still would go up/down while holding button), but after a couple of power cycles, that cleared up. Some weird byproduct of code updates I'd guess. Just a bit odd.

Anyway, looks like it is, at least initially, doing better after the software update to the transmission.

Did this issue ever come back? I'm experiencing same behavior on my XC60 2018. Sometimes, followed by 'Parking Brake Temporarily Unavailable' error. I'm thinking about replacing ABS Sensors. My dealer recently updated software and checked all cables but the issue still persists.

 

[osi07]

Has anyone ever found a solution for this? I have a 2020 b4 with the same problem.

 

[BimmerBill]

Our 2015 XC70 T6 had that "bumping shift" issue (it was both up and down shifts) at around 40K miles, and it was taken care of with a software update to the transmission. Low speeds only, and I can see that it might be blamed on brakes because we're slowing/braking before the downshift. But upshifting was getting bumpy too. We now have 110K on it and it is just now starting to feel rough when shifting again. I'm pretty sure it could use a fluid change.