Disabling ABS?

Jolfa · 30-08-12, 09:19 PM

My new 90q has got the ABS button but it doesn't appear to work, it switches off fine when the diff is locked, but not on the switch. Is it likely to be a switch fault?

Can I just permanently disable it by cutting a wire or something?

Stuart16v · 30-08-12, 09:58 PM

Don't quote me on this but when I take the fuse out on my 95 Coupe it runs just fine and the light stays off, try that maybe.

sam · 30-08-12, 10:12 PM

pull the fuse and the bulb from the clocks... had no ill effects on my 90q done this way and brakes get abused...

Jolfa · 30-08-12, 10:17 PM

Well that's that then, cheers guys!

Hanuman · 30-08-12, 11:24 PM

As a very quick response, (late night guessing) if the ABS is otherwise fully functioning, I'd say there is a switch fault, or someone may have simply bypassed the switch to overcome a witch fault.

The problem that you have is that the abs should be either fully operational, or the system completely missing for the purposes of the MOT (if I understand the requirements). So whatever you do, you should make the the effort to do it in such a way as to make it easily reversed if required.

I'll dig through my various antes later after another think.

Jolfa · 30-08-12, 11:29 PM

The problem I've got is that the ABS kicks in nearly every time I brake, even gentle braking at low speeds.

I'm sure I could address the problem and fix it, but I don't like ABS anyway

Hanuman · 30-08-12, 11:46 PM

That sounds like sensor issues. Often, the system just needs a good clean up of the sensors at the hubs.

There is a relay which enables the system assuming that a number of parameters are met.

-The supply line must be above a minimum voltage.
Recently, when I lost the output off my alternator, system volts dropped below 9 volts before the ABS switched off.
-it compares signals from all sensors. 4 wheels and later systems with the accelerometer. At standstill, it can only verify that the sensors are providing some input. It isn't until the car starts moving that it can compare the signals from all the wheel sensors. Often, bad sensors, dirty, or damaged drive shaft toothed rings will result in a system fault after moving away. I recall a distance of about 60ft(?)
-switches. Diff lock and the ABS on/off. The on/off switch resets each time the ignition is turned off. Ie. it should default to on every time.

The idea of all this is to have a fail safe. The light being part of that.

msh · 31-08-12, 05:53 AM

Agree about sensors. Sounds like rusty tooth rings or sensors themselves too far from the rings. About the switch - it's likely that the contacts inside are dirty, I had the same problem with my A90q after it spent two years in a garage, I was too lazy to take it apart and instead quickly pushed it for a couple of minutes. Now it usually works, in worse case on second or third attempt.

P.S. Last winter tried ABS in snow, having the car equipped with very old all season tyres with 3-4mm thread - to get the ABS kick in, the principle was as usual - I had to brake harder than I wished

Of course, there is some situations when ABS is not good, for these there's that switch

Hanuman · 31-08-12, 06:58 AM

Toothed rings.

The ABS sensors are looking at toothed portion of the drive shaft. As the shaft rotates, the ecu sees a pulse waveform from each of the wheel sensors. It compares these initially from standing to moving, to see that all wheels are turning. If the signals are comparable, all sensors are good.

It then continues to monitor these waiting to see when one signal is changing by more than all the others. Locked wheel. It then does its thing on that line. Release left or right front, or rear (one line, so both released)

If under braking, the ABS is kicking in early, then it must be seeing a bad signal. The signal is not so bad that it fails the comparator. But bad enough to indicate a locked/locking wheel.
rusted sensor rings on the drive shafts are common. Most common on the front. Some suggest that front left is worse than righ. My ur demonstrated many of the same issues, and it is surprising how bad the rings can be before the system can no longer cope. Damp increases the problems.

The Sensors are easily removed and reseated on the later cars. Wipe them off. Have a look down the hole with a small torch, and you should be able to pull out any debris in there.

The switch in the dash is a simple illuminated switch, common to yours, used on my V8 also.

rtz62 · 31-08-12, 07:00 AM

From an Objective point of view, don't disable the ABS; if you have an accident and there is any inspection of your car and it shows it was disabled / inoperative, you'll have no claim.
However, pressing the button to disable a properly-functioning abs system is totally different....!

30-08-12, 11:24 PM	#5
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,016	As a very quick response, (late night guessing) if the ABS is otherwise fully functioning, I'd say there is a switch fault, or someone may have simply bypassed the switch to overcome a witch fault. The problem that you have is that the abs should be either fully operational, or the system completely missing for the purposes of the MOT (if I understand the requirements). So whatever you do, you should make the the effort to do it in such a way as to make it easily reversed if required. I'll dig through my various antes later after another think. __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

30-08-12, 11:46 PM	#7
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,016	That sounds like sensor issues. Often, the system just needs a good clean up of the sensors at the hubs. There is a relay which enables the system assuming that a number of parameters are met. -The supply line must be above a minimum voltage. Recently, when I lost the output off my alternator, system volts dropped below 9 volts before the ABS switched off. -it compares signals from all sensors. 4 wheels and later systems with the accelerometer. At standstill, it can only verify that the sensors are providing some input. It isn't until the car starts moving that it can compare the signals from all the wheel sensors. Often, bad sensors, dirty, or damaged drive shaft toothed rings will result in a system fault after moving away. I recall a distance of about 60ft(?) -switches. Diff lock and the ABS on/off. The on/off switch resets each time the ignition is turned off. Ie. it should default to on every time. The idea of all this is to have a fail safe. The light being part of that. __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

31-08-12, 06:58 AM	#9
Hanuman Trickster Classic Audi Club Member Join Date: May 2009 Location: Heckling from the cheap seats, Phnom Penh, KoW Posts: 7,016	Toothed rings. The ABS sensors are looking at toothed portion of the drive shaft. As the shaft rotates, the ecu sees a pulse waveform from each of the wheel sensors. It compares these initially from standing to moving, to see that all wheels are turning. If the signals are comparable, all sensors are good. It then continues to monitor these waiting to see when one signal is changing by more than all the others. Locked wheel. It then does its thing on that line. Release left or right front, or rear (one line, so both released) If under braking, the ABS is kicking in early, then it must be seeing a bad signal. The signal is not so bad that it fails the comparator. But bad enough to indicate a locked/locking wheel. rusted sensor rings on the drive shafts are common. Most common on the front. Some suggest that front left is worse than righ. My ur demonstrated many of the same issues, and it is surprising how bad the rings can be before the system can no longer cope. Damp increases the problems. The Sensors are easily removed and reseated on the later cars. Wipe them off. Have a look down the hole with a small torch, and you should be able to pull out any debris in there. The switch in the dash is a simple illuminated switch, common to yours, used on my V8 also. __________________ I wish they would keep the damned Chinese away now that I can go home, so that I can enjoy Fish amok and a draught Angkor

30-08-12, 09:58 PM	#2
Stuart16v Newbie! Join Date: Aug 2012 Location: Carnoustie, Scotland Posts: 15	Don't quote me on this but when I take the fuse out on my 95 Coupe it runs just fine and the light stays off, try that maybe.

30-08-12, 10:12 PM	#3
sam Grown up member Classic Audi Club Member Join Date: May 2008 Location: North east Posts: 778	pull the fuse and the bulb from the clocks... had no ill effects on my 90q done this way and brakes get abused...

30-08-12, 10:17 PM	#4
Jolfa Grown up member Classic Audi Club Member Join Date: Apr 2010 Posts: 349	Well that's that then, cheers guys!

30-08-12, 11:29 PM	#6
Jolfa Grown up member Classic Audi Club Member Join Date: Apr 2010 Posts: 349	The problem I've got is that the ABS kicks in nearly every time I brake, even gentle braking at low speeds. I'm sure I could address the problem and fix it, but I don't like ABS anyway

31-08-12, 05:53 AM	#8
msh 4 ring whore! Join Date: Jun 2008 Location: Rucava, Latvija Posts: 3,816	Agree about sensors. Sounds like rusty tooth rings or sensors themselves too far from the rings. About the switch - it's likely that the contacts inside are dirty, I had the same problem with my A90q after it spent two years in a garage, I was too lazy to take it apart and instead quickly pushed it for a couple of minutes. Now it usually works, in worse case on second or third attempt. P.S. Last winter tried ABS in snow, having the car equipped with very old all season tyres with 3-4mm thread - to get the ABS kick in, the principle was as usual - I had to brake harder than I wished Of course, there is some situations when ABS is not good, for these there's that switch

31-08-12, 07:00 AM	#10
rtz62 Senior Member Join Date: Nov 2008 Posts: 1,527	From an Objective point of view, don't disable the ABS; if you have an accident and there is any inspection of your car and it shows it was disabled / inoperative, you'll have no claim. However, pressing the button to disable a properly-functioning abs system is totally different....!