Brake pressure sensors - is this they?

[John Brennand]

A big thanks to Dave (reggit) who has just read the error codes on my 2006 XC90 2.5.

Its for the Anti Skid Service error message and the code was BCM-0133 - indicating a faulty reading on "brake pressure sensor 2". Indeed when he looked at the readings, sensor 1 was in normal range (when brake went from, off to on) whilst number 2 was clearly out of range. I forgot to write down the actual numbers !

So the plan is... first to check the wiring/connectors and clean them with contact cleaners. If that doesn't fix it, I will replace unit 2.

Therein lies the issue - where are they !

I assume they are in the servo unit as shown in the attached photo. Is that them? If not where are they hiding? If so which is number 1 and which is 2?

Also, are there any tricks to be aware of when (a) pulling off the electrical connectors and (gently!) cleaning the contacts - and - (b) removing the offending sensor (is there any brake bleeding involved?).

Thanks for any input - John

[gmonag]

Those sensors on the servo unit are the pedal position sensor (L) and pressure build-up valve (R). From VIDA:

The brake pressure sensors are positioned on the master cylinder. One sensor is located on the primary circuit and one on the secondary circuit. The information is transmitted via two analogue signals (measurement range 0-5 V) and is used by the brake control module (BCM) to calculate the brake pressure during active yaw control, and when the driver applies the brakes.
The sensors are supplied with voltage via the brake control module (BCM). There are diagnostics for the sensors.
When replacing the brake pressure sensor, the brake control module (BCM) must be calibrated according to the information in VIDA vehicle communication or manually according to the test drive.

Never seen them myself.

[John Brennand]

Originally Posted by gmonag

Those sensors on the servo unit are the pedal position sensor (L) and pressure build-up valve (R).

Never seen them myself.

Cheers. That rules them out then !

Anyone else got a more precise location in relation to the master cylinder - e.g. a link to a picture or similar.
Too dark/cold/wet to mooch about now - I will investigate tomorrow in the absence of anyone's know how, and have a peek in the Haynes.

just spotted this from Clan in another thread which gives some more info ....
https://www.volvoforums.org.uk/showthread.php?t=265557

[Bagnall]

I had anti skid code, which turned out to be one of the brake pressure sensors

I have a 2005 2.5 xc90 D5, if it helps I changed both of mine, they are behind the abs pump on the right hand side of the engine as you lift bonnet.

Unsure if yours is the same 😐

[John Brennand]

Originally Posted by Bagnall

I had anti skid code, which turned out to be one of the brake pressure sensors

I have a 2005 2.5 xc90 D5, if it helps I changed both of mine, they are behind the abs pump on the right hand side of the engine as you lift bonnet.

Unsure if yours is the same 😐

Cheers will take a look there. There are some piccys here that seems to show them...

https://www.volvoforums.org.uk/showt...=237402&page=3

https://www.volvoforums.org.uk/showthread.php?t=239454

[Bagnall]

Yup that’s them. They’re not hard to find.

Searching eBay will show you what your looking for too

[John Brennand]

Originally Posted by Bagnall

Yup that’s them. They’re not hard to find.

Searching eBay will show you what your looking for too

Any tips for changing them over?

Is removing the electrical connector tricky - requiring multiple non-intuitive tab pushes?
Its a 27mm deep socket - I believe?
Brace it with a x-head screwdriver through the top hole on the union?
Working quickly - out and in - should cause very little fluid loss and so no bleeding required ?

Anything else ? John

[Bagnall]

If your able to attempt the fix yourself, I’m sure some skills with a small flat head will remove the connectors. I can’t remember exactly, but they’re all bloody fiddly! Why do they make them all different?

I didn’t attempt to remove the 27mm, I got two sensors from a breakers which cut the pipes.

So I did a quick spray with wd40, braced the sensor and removed the small pipes either side, quick swap and done.

Didn’t bleed mine, as you said hardly lost any fluid. No problems with them since.

Straight forward to be honest. Your biggest problem will be Storm Jorge!

[John Brennand]

As predicted...

Took a quick look this aft and fell at the first hurdle. I can't for the life of me see how the electrical connector releases off the bottom of the sensor and how the one at the other end of the lead disconnects either.

Can anyone say for sure how to release the two connector ends?

Its also a bit cramped in there so not sure my big hands will be able to release the unit from the union so may have to go for the brake pipe release - hence only the one to get off ! However there are 2 nuts holding each brake pipe to the union - do they both come off ?

[John Brennand]

Just to complete this thread for posterity.

I decided to order a used sensor from eBay (£20) with the intact electrical connector still on it. When it came it was obvious how to remove the connectors.

To remove the old one, it is far easier and there is much more room for big hands, if you remove the engine stay bar - quick and easy just 3 bolts.

Pop the connector off the bottom and WD40 the connector joint. I do have a 27mm deep socket, but found it easier to get a 27mm Flexible head ring spanner on it. With my lad holding the union bit with both a screwdriver through the hole and a spanner on the top (belt & braces) a quick tug and I cracked the sensor off easily.

Opened up the brake fluid reservoir and then unscrewed the sensor fully by hand. With an old rag underneath, a few ml of braked fluid came out and I quickly screwed the new one in by hand and tightened it down with the flexi-spanner.

Replaced the connector and engine stay bar. There was no need to top up the brake fluid as the level had barely altered.

Worryingly, on start up the error message was still there, but - after a run around the block and a restart all was clear.

Thanks to all who contributed. John