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What does Brake Assist Service Required mean? Topic is solved

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June
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What does Brake Assist Service Required mean?

Post by June » Tue Jul 31, 2018 8:03 pm

A couple days ago this message appeared while driving in a rainstorm. It went away the next time I started the car and has not reappeared. I called my service advisor back home who said not to worry. Has anyone had this message and what was wrong? Thank you, June
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Re: What does Break Assist Service Required mean?

Post by mrbrian200 » Tue Jul 31, 2018 9:14 pm

Your car has DTSC? Oh wait. Of course it does.

I mentioned this system in another topic recently. I'm pretty sure that message refers to the system that senses a quick press of the brake pedal and applies more brake pressure faster than your foot on the pedal alone would. It's meant to assist in the quicker application of full braking power during an emergency stop. Only DTSC equipped vehicles have this feature in your model year range.

This is just an educated guess, my high suspicion is that the key sensor in the system, the brake pedal position sensor mounted to the brake booster under the hood, is likely the culprit. It's known to give trouble as these vehicles get a little older. I replaced mine at around 100k miles.

Normal braking performance wouldn't be affected. If the pedal position sensor is the cause, you may also find that the cruise control refuses to engage while the fault is active. Restarting the car often clears active fault condition (and cruise control functionality).

If this is the case, VIDA should show a stored fault for the brake pedal position sensor.

It should be considered safe to drive the car for the remainder of your vacation. In normal driving you probably would never notice a difference.

If you need to stomp hard on the brakes for some reason you might find that the brakes don't feel quite as quick and grabby as you may have experienced in the past during an emergency braking maneuver/situation. In effect the brakes would feel like STC equipped vehicles without the assist function. Which may or may not make a difference as your stopping distance with the brake pedal jammed to the floor is governed by the condition of the pavement, tires, pads/rotors, and the ABS system doing it's job to prevent wheel lockup. I think it accomplishes full brakes something like 100-300 milliseconds faster than quick foot pressure alone does. **milliseconds** as in I doubt in the vast majority of accident scenarios it makes any real difference whatsoever.

I believe the functional part of the system that applies hydraulic brake pressure is contained within the BCM. If those parts were at fault I would probably expect ABS system warnings. But I'm not sure about that.

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June
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Re: What does Break Assist Service Required mean?

Post by June » Tue Jul 31, 2018 9:45 pm

Thank you so much! I've been worried about it. My car has 165K now so that is way past 100K and in service since Christmas 2003 so 14 and a half years. I'll take it in next week when I get home. Is the sensor hard to change? June
My Volvo cars owned
1989 740 GLT ordered
1994 850 4door standard shift ordered
1996 960 ordered
1998 S90 ordered totalled after 3 weeks
1998 V70 GT dealer stock car
2002 S80 T6 ordered totalled
2004 S80 T6 dealer stock car and current car owned

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Re: What does Break Assist Service Required mean?

Post by mrbrian200 » Wed Aug 01, 2018 6:51 am

I did a little googling on this just to make sure I'm in the right track. Yes, this is most certainly the brake pedal position sensor.

Sensor takes 10 minutes to change. The retaining ring/circlip can be a little fussy to release as it is oriented in a way that makes it a little difficult to reach/grab with the tool, otherwise it would take 3 minutes. So labor should be 1 hour +diagnostic fee +part.

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Re: What does Break Assist Service Required mean?  Topic is solved

Post by June » Mon Aug 06, 2018 10:14 pm

mrbrian200 wrote:
Wed Aug 01, 2018 6:51 am
I did a little googling on this just to make sure I'm in the right track. Yes, this is most certainly the brake pedal position sensor.

Sensor takes 10 minutes to change. The retaining ring/circlip can be a little fussy to release as it is oriented in a way that makes it a little difficult to reach/grab with the tool, otherwise it would take 3 minutes. So labor should be 1 hour +diagnostic fee +part.
Mrbrian200 you were completely correct! Thank you so much for putting my mind at ease! The car drove perfectly the rest of the trip and the message never came back on, but indeed it did store a code for the switch so my shop fixed it. I attached a photo of the bill. June
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My Volvo cars owned
1989 740 GLT ordered
1994 850 4door standard shift ordered
1996 960 ordered
1998 S90 ordered totalled after 3 weeks
1998 V70 GT dealer stock car
2002 S80 T6 ordered totalled
2004 S80 T6 dealer stock car and current car owned

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Re: What does Brake Assist Service Required mean?

Post by abscate » Thu Sep 13, 2018 7:43 am

edited title for search on text string for next gal/guy
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Re: What does Brake Assist Service Required mean?

Post by mrbrian200 » Fri Sep 14, 2018 1:17 pm

Interesting they replaced the stop light switch also (8622064). Since I didn't run the diagnostics I'll not officially question it. I'll just leave it at 'interesting'. It's possible likely they know something I don't (eg the message can be caused by either part failing, so to prevent the possibility of a return they replace both at the same time as standard practice).

For somebody like me who has replaced that on my own car, the total bill (over $500) makes me a little faint. But I suppose that's why I work on my own. I'm simply not accustomed to the costs associated with handing the car over to somebody else (who needs to make a living at it).

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