ABS ECU sorted - DIY

[finny 0]

The dreaded ABS light had been coming on and off more recently and decided to have a go at fixing it. I’m not very mechanically or electrically minded but always willing to have a go and learn from experience. Disclaimer: working on your own or someone else’s brakes and braking system are done entirely at your own risk and own competence. Apart from that I didn’t find it too difficult………………..

Tools:

4mm hex socket but E5 torx socket better

¼ drive wrench

Precision screw drivers

Flat head screw drivers

Dremel if required

Useful vice and another clamp

Junior Hacksaw

Stanley knife or scalpel

Soldering kit

Lacquer (nail varnish)

High temperature sealant

Freezer bags, cable ties, old rags/ old clothes,

To remove ABS pump if required:

10mm socket,

11mm spanner,

Brake fluid,

Brake bleeding kit

VAG-Com (but not necessary)

Removing the ECU: On my OBII, 96 Highline, the ABS ECU is attached underneath the ABS pump in the engine bay. There are 4Nr bolts to undo from underneath the ECU. The heads are along the edges in a recess of the ECU. I used a 4mm hex socket and 1/4 drive wrench and 3 of the 4 bolts came undone and off quite easily, but the most accessible bolt (nearest left), the head of the bolt started to round off.

Originally my search on the Web revealed either a 4mm hex or E4 torx socket was better. I found an E5 torx socket was actually the correct fit for the bolts. However still couldn’t get the last bolt off due to awkward and limited access. To avoid getting grease on my clothes from the bonnet locking mechanism (on the slam panel), I put a rag over it the lock when leaning over the engine.

If all 4 bolts can be removed then there are just two bits of wiring to disconnect. The first being the main loom that that comes off by pulling out a tab (towards you) and then the connector can slides up and away from the ECU. The 2nd wiring is just the ABS pump connecting block. Then it’s a case of wriggling the ECU free from underneath the pump and around the brake lines.

Removing ABS pump and ECU if required: For me there was no alternative except to remove the whole ABS pump and ECU complete from the bulkhead/ firewall. The ABS pump unit is held by 3 Nr 10mm bolts on top and cracking opening and undoing 6nr brake unions from the front with 11mm open spanner. Slow process due to closeness of brake lines. Used a load of old clothes to collect and soak up the brake fluid dripping down from the exposed brake lines.

The whole ABS unit is now free from its holding bracket and you have to wriggle it out and push some of the brakes lines out the way to get it clear.

Now with the ECU still bolted to the ABS pump, I’d put it in a work vice and used pliers/ mole grips to try and turn the remaining bolt loose. No good due to the tight recess around the bolt. So got the Dremel out and grounded off the head of the bolt and use pliers to twist and release the bolt. If haven’t done so already, the pump wiring that just clips (two pin connector) into the ECU can be pulled out, to completely separate the ABS pump and ECU. What you will find is that there are 10Nr cups on the ECU side and with pins on the ABS pump side.

At this stage the car was obviously not drivable but you can refit the ABS pump back and reconnect the brake lines, refill with brake fluid and bleed the brakes. I tried to bleed the ABS pump via the VAG-Com (unregistered) but it wouldn’t let me (being unregistered software). I had no issues using normal brake bleeding procedure to bleed all the brakes anyway.

I also temporially put a freezer bag underneath the pump to cover the pins/ pistons from dirt/water and cable tied it to the pump and also a bag over the ABS loom connectors. The car was now drivable but the ABS light will be constantly on and obviously no ABS feature.

Back to the ABS ECU; there are 4nr tiny ring clips that need to be remove from where the bolts go through, this can be done using the precision screwdrivers (ones you get in those little clear plastic boxes, only a few quid from Maplins). Don’t loose the rings clips as they need to be refitted.

Using the vice, the ECU is clamped where I used a junior hacksaw and gently saw through the sealant indent line around the unit where the two halves meet. This is very easy to do and don’t get carried away as its only sealant you are going through. Using a small flat head screwdriver or two, gently prise the ECU apart. I found there was a plastic tab between the two closest bolt holes, as I didn’t saw too hard, this remained intact.

So now you are looking at a PCB, look hard enough and you’ll see probably see some dry joints which is likely to be the source of the problem. These can be all over the place and generally these are the larger soldering points that need attention or where the main connecting loom would sit.

STOP: if you have never soldered before or no good at it. Don’t bother, send the unit away to someone who knows what they are doing re: soldering.

However I did have a go. The PCB is covered with a clear membrane which needs to be cut with a scalpel and lifted off before any soldering; I ended up with lots of tiny bits of membrane and vacuumed out the bits out.

My joints were rubbish and joined on to the next joint etc, it was a mess. Once finished, you should covered up the joints with the membrane or put some clear lacquer to protect the new joints. I didn’t bother just yet as just in case the fix didn’t work (knew it wouldn't). Refitting is reversal of removing expect the pump is already on the car. Unfortunately the ABS light was still on and now the handbrake light stayed on. Using VAG-Com, it acknowledged the ABS ECU but could no longer communicate with it.

So this time I removed the ECU only and just sent away to Starsoldering http://www.starsoldering.co.uk/ to sort out my mess and re-do for me. The turn around was quick.

Refitting the ECU: I agreed that I would reseal the unit up myself; this was done using some high temperature heat resistant black sealant from eBay and applied around the edges of the unit. Used my vice and another clamp to hold the unit tightly together overnight. Refitted the small ring clips around the bolt holes.

Refitting the ECU back underneath is still fiddly and I gently forced the brakes lines aside to get the pins underneath the pump to slot into their cups on the ECU but at least the unit was smaller this time round. Connected the pump wiring at the back for the ABS pump and the main ABS loom, this kind of ramps/ slides down when you push the tab forward i.e. it will not connector together if you push it vertically straight down, its slides in effectively.

Using the E5 torx socket and ¼ drive wrench and do up the 4 bolts (mine just 3 for now).

I fired up the car and the ABS light disappeared, released the hand brake and the handbrake light went out. Happy days

More info: While the ECU was off I did find some more useful websites which explain the procedure and quite common with Volvo owners as the ABS ECU is the same, as with the fault. The fix has worked for most and their soldering skills are better than mine.

http://www.freewebs.com/dacvolvo/absrepair.htm

http://www.matthewsvolvosite.com/forums/viewtopic.php?f=1&t=12651

http://www.starsoldering.co.uk/

I’ve read that these re-soldering fixes can fail again. It hasn’t done so yet but I can only assume this is dependant on the soldering and the solders deteriorate due to heat, vibration etc over time.

Easier part was splitting the ECU unit open, most difficult for me was soldering = Fail, best to send the ECU away. Most annoying had to be removing the ABS pump unit in order to get the ECU off.

Hopefully this is may be useful for anyone attempting the fix themselves, otherwise there are firms out there who do this as a business and provides guarantees apparently. This DIY fix unfortunately doesn’t.

[roosevelt1st 1]

This deserves to be a 'sticky' thread! Congrats on such a thorough write up.

[veeare6 0]

It could not have been put any better... I wish I had signed up on this forum a long time ago... wouldn't have had to figure it out on my own..

[finny 0]

Thanks, done over 500 miles since and always a relief to see the ABS light go out when starting up the car.

[Timah89 1]

very well put, been meaning to get round to doing mine for the last 2 weeks, but will be doing it this week for sure, problem now is the car wont start at the moment

[VR6-DUB 3]

Finny just curious to know how long did it take you to do, start to finish? And also are you looking to do anyone elses on here? How much you looking to charge for this to be done on someone eleses vr?

[finny 0]

If its just removing the ABS ecu, then its not even a 10 min job, providing none of the 4 bolts are rounded off.

Splitting the ecu apart is quite simple but unless you know what you are doing with the soldering part I would send it off to get done. The chap I used I guess could split the unit and reseal it again.

If your local to me I could remove the ABS ecu for you or show you how to - no charge and hopefully with no stuck bolts.

cheers,

[varr6pete 0]

Very interested in your repair, I have had an ongoing problem for more than 9 months, I paid for a specialist to use his equipment to check the problem, and it came up with a rear offside sensor. Changed all sensors it passed mot, but the light came back on again but is intermittant,. Rather than pay the specialist another £75, is the VAG unit you mention accurate enough to isolate specific abs problems and who sells it and for how much? ps live in Reading cheers Peter

[finny 0]

The VAG-Com unit?, eBay for the third party cable and basic software (unlicensed) ones about £10 or genuine Ross-tech ones - registered/ licenced with support circa. £260.

Its probably the ABS ecu as I had the same fault as you as well as replacing sensors. The problem is that the soldering type done back then becomes brittle and fail.

Try the chap I used. No guarantee it will work as he dosen't have facilities to test the ecu but worth a punt? or go with companies that fixes these as a business.

[varr6pete 0]

Thanks for that, can you give me your repairers details? May consider buying a used ecu, then swopping over once its resoldered?

[finny 0]

Before you buy a used ABS ecu, you need to check that it matches your existing one. There are number of versions out there so you need the right part nr. Also if your pump was say faulty, you will need the right pump so check part nrs match. The pump part nr will be on a sticky label (hopefully) and for the ecu will printed on the underside.

The chap I used is Starsoldering.co.uk - links in my write up

[varr6pete 0]

Thanks Finny, can you confirm what the link between the handbrake light and abs? my handbrake light is ok? and secondly did you VAG tester show an ecu fault? hence its removal etc....

[finny 0]

No link between handbrake light and abs, its just I screwed up soldering so must have affected the PCB. Previously to that, the only time handbrake light on, was due to low brake fluid.

My VAG-Com only indicated error with rear abs sensors but from reading up (after changing the sensor) for the abs light still coming on, must mean it was the ABS ecu.

No expert, but I would think its the ABS ecu PCB joints needs to be redone. I would remove your existing ecu and send it off (by Special Delivery) for fixing.

[Timah89 1]

you got a pick of your pump an ecu as i swear i cannot locate 4 bolts that hold the ecu onto the bottom of the pump. there are several clips around the perimeter of the ecu casing???

[gary.scales 0]

good write up, I think I have the same problem, at the MOT last year the vag-com picked up a sensor issue NSF, got this replaced, light went out, MOT passed, drove out of the garage and light came back on, now is intermittent. Proably my ECU then!! Cheers!

[finny 0]

Tim, click on one of the links in the write up for pics from others.

You are right, that they are along the perimeter of the casing underneath.

[finny 0]

good write up' date=' I think I have the same problem, at the MOT last year the vag-com picked up a sensor issue NSF, got this replaced, light went out, MOT passed, drove out of the garage and light came back on, now is intermittent. Proably my ECU then!! Cheers!

[/quote']

For me it was the opposite. 2 years ago car failed MOT as the ABS light came on during the test. Drove it out and the light went out half a mile down the road. Turned around and went back to the MOT station. The guy came out, switched off the engine and then fired up the car and the light went out . Gave me a pass then. However the light started to come on more often.

Hope its a permanent fix - well at least for a couple of years. Not really sure when an untouched ABS ecu starts to fail 5yrs/ 10yrs? mine lasted 13yrs.

[gary.scales 0]

mine lasted 13 years too! Do you have the name/number of the guy that did your ECU or know any sites/companies that do this?

[finny 0]

Click on the green arrows in the write up.

Other people I can think of are ecu-testing.com or BBA-reman. Never contacted these people.

The guy I used, doesn't have anything to test the PCB so there is no guarantee. But he did a very good job.

cheers

[gary.scales 0]

Thanks a lot! Cheers

[varr6pete 0]

contact star soldering at http://www.starsoldering.co.uk/

Will be sending my ecu to him asap

[Timah89 1]

cheers finny, i'll have a look now.

[varr6pete 0]

Hi Finny, just to clarify, are you saying I can remove ecu and continue using the car until ecu is fixed? Will there be any risk to the wiring, ie no receiving signals etc if used without ecu in place. I know I will have normal braking just can't be without the car at the moment, but need ecu to be resoldered...

[finny 0]

Yes, bag up the pump's pistons and use string/ cable ties to make sure the pistons underneath won't attract dirt/ water and bag up the ecu's loom connector.

It was absolutely fine when I drove my car in this state for 2 or 3 days.

But if you can avoid driving it I would, only beacuse you have 'tampered' with the car braking system. ie physically removed the ecu rather than its there as it should be but nevertheless faulty, if you see what I mean?

I reckon send it 1st class Special delivery on say a Monday, arrives Tuesday and gets worked on, leaves overnight for ecu to be sealed up and chap sends it back late Wednesday and you may get it back Thursday?. So min 4 day turn around.

Hope the fix works for you, cheers

[varr6pete 0]

Thanks