ABS triggering on light braking...

[DavidMeredith 10]

Hi all

 

Just wondering if I am missing anything obvious before taking car to garage for an ABS issue (VR6). Over the years previous to now the ABS either worked or the light was on and it didn't (probably in about equal measures -- either the light didn't go off at start or would come on part way through a drive) but it has always behaved itself on MOT day.

 

Now I have a new issue. Mostly the ABS light goes off after the start up check procedure and all seems well until I drive off.... then I hear rapid clicking sound and next time I touch the brake pedal the ABS kicks in (the light stays off). Sometimes though the ABS light oomes / stays on and then it doesn't happen.

 

I have WD40ed the connectors on the front sensors, which are reading ~1100 ohms resistance. The sensors look clean and the sensor rings look ok although a bit rusty (does this matter?). I've not taken back wheels off as I can't see that I can do a lot there, but maybe I will when it stops raining. Unfortunately, I don't have a fault code reader...

 

I have solved the issue for now by disabling the ABS (unplugged a front sensor), but I'll need to sort it out at some point. I've probably reached the limit of what I know (ie what I have found on the internet!) and just wondered if there was anything else I could try before biting the bullet?

 

Sorry if I have missed anything out, I'm not that mechanically minded, so any help appreciated!

 

Thanks, David

[Dox 23]

 

 

 

Now I have a new issue. Mostly the ABS light goes off after the start up check procedure and all seems well until I drive off.... then I hear rapid clicking sound and next time I touch the brake pedal the ABS kicks in (the light stays off). Sometimes though the ABS light oomes / stays on and then it doesn't happen.

 

 

 

 

 

Thanks, David

 

It sounds like the air gap between one of the sensors and its reluctor ring is varying triggering the ABS into thinking a wheel is locked (each sensor counts the segments of the reluctor and the ecu compares them to determine if a wheel is locked).

 

I'd check the condition of the reluctor baskets on the back of the rear disks first

[DavidMeredith 10]

Thanks Dox -- will I be able to check those by taking the wheel off? I had a quick look under the car and it all seemed much more enclosed at the back...

 

Cheers, David

[Dox 23]

Thanks Dox -- will I be able to check those by taking the wheel off? I had a quick look under the car and it all seemed much more enclosed at the back...

 

Cheers, David

 

No, you will need to dismantle the brakes and remove the disk to inspect the sensor / reluctor.

[DavidMeredith 10]

Ah, ok, I think that it a bit outside my spannering comfort zone -- I suspect I could take them apart, but whether I could get them back together again and working is another question! I think I'll pop it in to the garage...

 

Thanks again, David

[Dox 23]

Well the other end is the ECU, its known for the windscreen seal to fail and water gets inside causing corrosion. Its located by the passengers left ankle behind a plastic panel, check the connector pins for corrosion, if OK open it up and check the PCB for corrosion also.

 

You'll only need a screwdriver to check this, but its recommended to remove the earth connection from the battery first.

[DavidMeredith 10]

Cheers, I'll have a look at the ECU before committing it to a garage... A quick search on the bay suggests that the ECU is not that pricey (~£30) so is it worth getting one and swapping it out if there is any evidence of water damage / corrosion? If it solves the issue great (and it will be cheaper than a garage diagnosis), if not I'll have a spare in case it does fail in the future.

 

David

[Dox 23]

You need the correct part number to match yours, so remove yours first.

 

Put a wanted advert up here, many of us have known good spares rather than hit and miss eBay stuff and it all helps to keep this community going

[a_riot 0]

Cheers, I'll have a look at the ECU before committing it to a garage... A quick search on the bay suggests that the ECU is not that pricey (~£30) so is it worth getting one and swapping it out if there is any evidence of water damage / corrosion? If it solves the issue great (and it will be cheaper than a garage diagnosis), if not I'll have a spare in case it does fail in the future.

 

David

 

I'd be a bit surprised if it was the ECU. They are pretty robust. I've heard of owners getting them submerged in water and they still work once dried out. It can happen though. My guess is that a wheel sensor is touching a speed ring somewhere. I think I have this going on as well at my right front wheel. The ABS will kick in, the brake pedal stays down briefly and I hear clicking. My ABS light doesn't go on and no codes are thrown, but I took a look when this was happening a few weeks ago and the ABS sensor was being ground down from making contact with the ring. I replaced the sensor and bent the ring a bit to avoid contact, and it stopped for a while, but now has started again. I think I might have an issue with that wheel hub or bearing, as I'm not sure why that would occur, but if you can spin the wheel and watch with a flashlight to see if its making contact that might be a good place to start. I think there are two different wheel sensor codes, one is the sensor has failed, likely getting an out of range voltage, and there is a mechanical failure code, which I think is the one that occurs when the sensor makes contact. If you can scan your system you might see one of those codes.

[Dox 23]

Post 30

 

http://the-corrado.net/showthread.php?104653-2-0-16v-Corrado/page3

[DavidMeredith 10]

Thanks both, a couple of things to look for -- I'll update!

 

Cheers, David

[a_riot 0]

I took a look at my ABS issue over the weekend, and the right front ring has rust on it in some areas, while the left is perfectly clean. Looks like the sensor is scraping against the ring in places causing the ring to rust where it makes contact, which then causes the ABS to kick in when its not needed. I used a screwdriver to try and slightly bend the ring out of the way of the sensor. But as I looked at it, I wondered how could it be that one ring is touching in places and the other isn't all things being equal.

It occurred to me that maybe the axle nut on the right side wasn't torqued up, allowing things to shift ever so slightly when the wheel steers, so I got a socket on it and it spun 1/8 of a turn with a quick impact burst. So I think it might not have been fully torqued down. Now that that's been done, no more ABS sensor scraping noises and no more ABS kicking in after making a sharp turn, especially in reverse. Car feels more solid on the road as well. Got to make sure those axle nuts are properly torqued. I usually put a black felt marker line across the nut and end of axle after torqueing them to be able to easily see if they are backing out, but I forgot to do it to this one. On to the next issue...

[DavidMeredith 10]

Progress... of sorts.

 

So, I found the ABS ECU (1HO 907 379E) and had a look, and there does seem to be a bit of water damage on the PCB (bottom, left of centre). Checked connector terminals and all looked shiny and bright. Put back together, and reconnected the front sensor that I had pulled to stop ABS triggering. Now ABS light is firmly on, doesn't flicker at all on startup and no signs of ABS doing self test. So, does that mean the ECU is dead, or does the ABS system have to be reset in some way after having been run with a sensor unplugged?

 

Good job I've got plenty of time until the next MOT!

 

Cheers, David

[a_riot 0]

So, does that mean the ECU is dead, or does the ABS system have to be reset in some way after having been run with a sensor unplugged?

 

If the ECU was dead, I don't think the ABS light would come on at all as I think the ECU is what triggers it, but if I recall correctly, some ABS codes are persistent, so even after a repair is made, the code needs to be cleared with VAGCOM to get the ABS light to shut off, but I don't recall which ones are...

[16v_alan 0]

To answer your question David, no the ABS won't need resetting after disconnecting and reconnecting a sensor. Should just be able to plug back in - check procedure will detect it's connected on start-up again.

 

I suggest clean the contacts of the one you unplugged. If you were driving around for any length of time with them disconnected there's a chance you could have collected dirt in there.

 

I'm doing some ABS whispering myself, similar symptoms. will update on here when I get to the bottom of it...

[swiftkid 1]

Mine does the exact same thing, been doing it for years and it's the ABS pedal sensor on the master cylinder. Well known for the connections to go crusty inside and there's a write up on here how to take it apart and clean it but I've got a full teves20 system to go on so never bothered. I think Stealth do a repair service on them

 

My symptom is when I'm at a relatively low speed I get a humming noise like a compressor with the ABS in full action. As soon as I touch the brake pedal its full brakes, annoying as hell but I've learn't to live with it. Also just to add, my ABS light is off as well.

[SteveM 10]

Mine was also an issue with the pedal sensor. Got lucky with a secondhand replacement and all has been well since.

[16v_alan 0]

Yeah, those are the symptoms Swifkid. And I had my BPPS repaired by Stealth too. Not too difficult to remove if you have a kebab skewer handy to unseat the circlip.

 

As well as that, diagnostics also suggested that front OS sensor and Rear NS sensor and Ring were faulty on mine. After replacing all parts with new and clearing codes, ABS began triggering consistently upon braking at low speeds.

 

On the off chance that I might find a quick fix, I cleaned up the old front sensor with WD40 and switched out the new one. One month later all is well, ABS light is behaving and I pray to the corrado gods every night.

 

To summarise, considering this and that there were no signs of mechanical failure to the Rear Ring, I recommend cleaning those pesky sensors before replacing – the fronts are accessible without removing, the rears aren’t accessible without popping off the brake calliper etc.

 

Hope that helps someone.

[DavidMeredith 10]

As promised, an update... rather delayed as I took the car off the road for the winter months as I wasn't using it much and the ABS light was now on all the time.

 

Anyway, earlier this month I finally bit the bullet and took it up to Stealth Racing. Diagnostics showed all manner of issues - the pedal position sensor, the ABS pump and most of the sensors. Just over a week later, and I had a heavily refurbed / renewed and most importantly working ABS system. Plus as a bonus, a much improved gearshift action, so thanks to Vince / the guys at Stealth!

 

Driving the Corrado again after a bit of time away did remind me what lovely cars they are :-)

 

Cheers, David