ABS Module???

the tenor man · Post by **the tenor man** » 13 May 2018, 12:32

Hello all and thanks for looking...

I have a 2004 S60 2.4 FWD 5 Speed Manual STC ...

Here's the trouble...I'm getting no brake (no Fluid) pressure to either of the two rear brake calipers. I have no ABS warning lights on the dash...nothing other than rust on the rear rotors.

I just thought I would ask to see if anyone has any ideas...could it be a defective module (the electronics part) or a bad pump...

Interestingly, I've been driving like this more more than two years and only gave it some thought when I discovered the rust on the rear rotor surfaces...

Any help would be appreciated...

The Tenor Man

Post by **abscate** » 13 May 2018, 13:14

The front brakes do about 4x more stopping than the rears so if you drive like me you could have the rear brakes fall off and barely notice.

If you are just using rust as the 'no pressure' diagnostic, you should remove the rear wheels and check the calipers for free motion - on these cars the calipers don't float, so it is more accurate to say watch the brake pads for motion.

The calipers are probably frozen up, especially if you don't follow the 2 year protocol for brake fluid refresh.

If it is just surface rust, resurface them at a shop, check the parking brake shoes while they are off , and you should be good to go with new calipers.

Post by **oragex** » 13 May 2018, 16:42

As above, I suspect you have already inspected the sliding pins? That would be the first step.

But it's also possible to have an issue with the ABS valve body or with the master cylinder. May as well be a failing flexible lines at the caliper if the car has more than 200K miles.

A leaking brake booster will also reduce significantly the braking power. Mine was leaking (hissing) near the pedals and the brake rotors were wearing only over a reduced area - see pic

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the tenor man · Post by **the tenor man** » 14 May 2018, 06:32

Thank you for the speedy replies...

My first thought was also frozen rear calipers, but I took it to the local mechanic that I have been going to for years to have the rear calipers changed (they are probably the originals), and he said the after doing one wheel and trying to bleed it, there was no pressure fluid pressure in the line. He also thought it could be a hose but ruled that out because both sides barely dripped.

After reading another post here, I don't hear the pump motor cycle when I first turn on the ignition key.

I think I may give the pump motor a slight smack with a small hammer and see if that may free-up the motor...otherwise, I think I'll just pull the electronic module board and send it out for repair...

Any suggestions would be greatly appreciated...

Thanks again,

The Tenor Man

Post by **abscate** » 14 May 2018, 10:15

The pump only gives pressure when ABS is activated - you have to be able to get clear bleeding from pedal action alone or else something is badly plugged up.

Try driving the car and listening between 10-20 mph - you will hear a slight burp as the pump self-tests.

Did the mechanic take off the hose and see if fluid ran clear? I hope so. If s/he just tried the bleeder and gave up....back to school.

the tenor man · Post by **the tenor man** » 14 May 2018, 11:19

Thanks for the replies...

If I remember correctly, he removed the right rear caliper, installed the new one and then tried to bleed it. He said at the time, only a trickle of brake fluid came out when he removed the old caliper. He said he thought that there could be a bad brake hose on one caliper but has never seen both brake hoses bad...he checked both...same trickle...

He also stated that the pedal was hard as a rock, but pushing the brake pedal still didn't force any fluid to the rear calipers.

He removed the new calipers and put the old ones back on...he doesn't think it's the calipers...back to square one...

The only thing that I can think of is that a piston(s) in the valve body is frozen or (this is a stretch) that the pump motor is stopped in such a spot and to inhibit the flow of fluid to the rear calipers.

OR the line from the ABS unit to the rear calipers has been crushed...somehow...

Yikes....

Tenorman

Post by **oragex** » 14 May 2018, 11:40

I too noticed a rather weak fluid coming out of the bleeders even when using the pressure bleeder. I guess the ABS valve unit gets some issue when mechanics force back the caliper pistons to install new pads/discs without opening the bleeder: this may mess the solenoids inside the ABS valve unit because of the back pressure although it doesn't always happen.

Post by **abscate** » 14 May 2018, 12:08

the tenor man wrote: ↑14 May 2018, 11:19 Thanks for the replies...

If I remember correctly, he removed the right rear caliper, installed the new one and then tried to bleed it. He said at the time, only a trickle of brake fluid came out when he removed the old caliper. He said he thought that there could be a bad brake hose on one caliper but has never seen both brake hoses bad...he checked both...same trickle...

He also stated that the pedal was hard as a rock, but pushing the brake pedal still didn't force any fluid to the rear calipers.

He removed the new calipers and put the old ones back on...he doesn't think it's the calipers...back to square one...

The only thing that I can think of is that a piston(s) in the valve body is frozen or (this is a stretch) that the pump motor is stopped in such a spot and to inhibit the flow of fluid to the rear calipers.

OR the line from the ABS unit to the rear calipers has been crushed...somehow...

Yikes....

Tenorman

Pop the soft brake hose off the hard brake line to diagnose collapsed or plugged hose

Then remove hard brake line at ABS to diagnose plugged hard line.

It’s much more common to plug hoses than hard lines, the insides collapse over time or old (>24 months) brake fluid

the tenor man · Post by **the tenor man** » 29 May 2018, 08:43

I thought I should post what repaired the rear brake problem I was having...

It turned out to be the ABS pump...I purchased a used one from eBay for $60.00 and mounted it (matching my pump number) ...as soon as I turned on the ignition, I heard the ABS pump motor operate...my old unit did not do this.

I was able to re-use my electronic module as the dash and VIDA showed no codes or faults with the ABS unit. I would believe that a bad pump should throw a code, but did not.

I was able to use the VIDA laptop (from Dave Leach) to activate the ABS motor which facilitated the bleeding of the brakes...

The rear calipers are working now and the pads are beginning to polish off the rust...

Many thanks to all who chimed-in to help and special thanks goes to Dave Leach who set up a laptop with VIDA and offered excellent customer service...

The Tenor Man

93SCMax · Post by **93SCMax** » 29 May 2018, 10:47

Nice follow-up! Thanks for sharing your solution.