Break Failure Stop safetly P0571 - my repair done nothing

[leyus]

I get Break failure stop safely notice with ABS light on.

Breaks keep working
Cruise control keeps working.
If I stop and turn off engine it goes away instantly
It comes up entirely randomly, I commute 60 miles one way sometimes both ways nothing, sometimes few miles and comes up.

I tried:
Replaced break pedal position sensor (used one from scrapyard). Still the same.
Replaced break light switch - new one from ebay still the same
Cleaned with contact cleaner break pedal position sensor connector and wrapped cables around it with electric tape -no change
Took it to my car mechanic he could not reconstruct this error, he claims he only 0074 error and he thought it was abs pump or ecu but previous owner regenerated those and provided me reference number for work done with lifetime warranty, so I am unsure of this diagnosis.

Patient is 2003 D5 V70. Any advice what to check and what else can I do will be appreciated. Is it possible that break pedal position sensor from scrapyard was simply bad and im looking in wrong direction ?

[Clan]

Originally Posted by leyus

I get Break failure stop safely notice with ABS light on.

Breaks keep working
Cruise control keeps working.
If I stop and turn off engine it goes away instantly
It comes up entirely randomly, I commute 60 miles one way sometimes both ways nothing, sometimes few miles and comes up.

I tried:
Replaced break pedal position sensor (used one from scrapyard). Still the same.
Replaced break light switch - new one from ebay still the same
Cleaned with contact cleaner break pedal position sensor connector and wrapped cables around it with electric tape -no change
Took it to my car mechanic he could not reconstruct this error, he claims he only 0074 error and he thought it was abs pump or ecu but previous owner regenerated those and provided me reference number for work done with lifetime warranty, so I am unsure of this diagnosis.

Patient is 2003 D5 V70. Any advice what to check and what else can I do will be appreciated. Is it possible that break pedal position sensor from scrapyard was simply bad and im looking in wrong direction ?

P0571 isn't a recognised volvo brake fault code..

I see you mention 0074 which IS a relevant code it means one or more electric vales in the hydraulic unit may be sticking. Has your brake fluid been changed every 2 years? You need to activate the hydraulic valves with your diagnostic tool and make sure each one clicks . Changing the Brake fluid may help if it has been neglected.

[leyus]

Originally Posted by Clan

P0571 isn't a recognised volvo brake fault code..

I see you mention 0074 which IS a relevant code it means one or more electric vales in the hydraulic unit may be sticking. Has your brake fluid been changed every 2 years? You need to activate the hydraulic valves with your diagnostic tool and make sure each one clicks . Changing the Brake fluid may help if it has been neglected.

Thank you for your answer, I have cheap OBD reader via bluetooth and use car scanner so maybe that's why.

I honestly don't know about break fluid I just bought it a week ago and car was rather neglected window not rolling back up and attached with gaffa tape, I fixed that. Mirror is going all the way up every time I enter, didn't deal with it yet. Only central speaker is working so I am expecting fuse or amplifier gone.

But I put fixing handbrake, window and this ABS issue as priority before I move to next thing. I will replace break fluid this weekend but if that doesn't help, is it just volvo that has this diagnostic tool to activate hydraulic valves or is it something all mechanics will have?

[leyus]

I checked paperwork and ABS pump refub was done on November 2023. As pump was send to regenerate it. I assume break fluid must have been changed when pump was removed from the car. I will contact company about warranty on it, unless anyone have any idea what can i DIY to resolve this?

[TeamG]

Originally Posted by leyus

I checked paperwork and ABS pump refub was done on November 2023. As pump was send to regenerate it. I assume break fluid must have been changed when pump was removed from the car. I will contact company about warranty on it, unless anyone have any idea what can i DIY to resolve this?

As Clan suggests, a brake fluid change would be a sensible step. Particularly if you know that the car has been neglected, as this is often a service item that is missed. It’s probably only £10 or so to do the change.

[stuart bowes]

never hurts to bleed brakes anyway

just get a pressure bleed kit and put enough fluid through each corner that you've effectively replaced the fluid

how much total fluid in the system? divide by 4 and get that much out of each corner

[4x4]

Originally Posted by stuart bowes

...how much total fluid in the system? divide by 4 and get that much out of each corner

Except there will be more fluid required to the rear calibers than the front

[stuart bowes]

yeah ok bias a little to the rear. but how much though, presumably not a lot