jackal2513

Hi guys, im out on a road trip. My ABD and ABS lights came on which i understand could be all sorts of different things but that@s not the problem. The problem is one time when i pulled away the ABD and ABS warning lights did not come the ABD engaged with the ABD green light illuminating. The whole car pulled strongly to the right and almost took me into the next lane ! This then happened for a second time. After that the ABD and ABS warning lights came on again.

Now first of all I was travelling in a straight line and over 60mph so the ABD should never have engaged. My guess is its getting a faulty reading or shorting or something. Chances are I wont be able to sort this whilst I am away but what I do need desperately to do is to make sure that the ABD never enagages again as it could pretty much kill me if it happened ***** nilly at the wrong time on the wrong stretch of road.

So, in short, does anyone know how to disconnect or stop the ABD from working. Is there a relay I can pull for example. Of failing that, can anyone say with absolute certain that once the ABD warning light comes on, the sustem shuts down and stop functioning (it certainly seems that way as it never happened again once the warning lights came on again)

Hope you can help .... thanks, Rich

bobt993

You can disconnect the connection between the ecu and and abs module I can look up the wire code in the shop manual . Never heard of abd causing what you described . Any water in the car under the seats ??

jackal2513

hi thanks, no water under the seats but i will check the front boot

i gather there are 3 relays to the left of the spare tyre ... maybe pulling one of them will nullify the ABD ?

one thing i remember was thath about the same time the speedo momentarily flicked to zero and then back again so I am thinking that a faulty speed sensor is causing all of this ... if the ABD doesnt know what speed its doing then it can engage at any time I would imagine.

Be good if you can get me that wire code Bob, thanks.

jackal2513

ABD is surely just a long pulse of braking administered by the ABS unit so pulling the ABS fuse should disengage ABD and ABS for good ? Or have I oversimplified.

bobt993

No, ABD in the 993 is pretty crude. The relays on the left side should not be removed. R65 is used by the control unit if return feed of the pump is required (ABS). R68 provides solenoid control of the ABS system. Jumping this relay will cycle the pump for test purposes. Throttle information to the ECU is provided by terminal 47 on the ABS control unit. If you unplug the ABS ECU and hold the harness in your hand with the wire end on the right side (looking at the pins) terminal 47 in on the upper right. Count backwards to the pin (top far right pin is 55 so count back to 47).This pin connects throttle information from the engine ECU to the ABS/ABD system. Wire is white/blue trace verify first with the pin 47 for continuity. It is only used to make the ABD system operate and not the ABS which is standalone. You can also remove the dash light Pin31 blue/brown wire and the ABD info light pin 32 white with green.

I am still not sure that this is your real problem, but the workshop manual the ABD will no longer function or even know the engine is one without pin 47 connected.

993KT

I think you most likely have a faulty rear wheel speed sensor. The tone wheel could be missing a tooth, or the sensor is too far from the tone wheel, or there is metal shaving that got into the sensor. You can do a visual inspection to make sure everything looks clean in there. Of course it could be intermittent electrical issue also, but my bets are the ones that I mentioned.

ABD is controlled via the ABS module. The ABS module monitors the wheel speeds and it takes a while to detect a fault if the WSS issue is intermittent. Once the fault is detected, ABS and ABD will stay off for the remaining of the drive cycle.

For the short term, I would suggest try unplugging one of the wheel speed sensor. This will be registered as a electrical line fault and it will disable ABS and ABD at vehicle start. (You may also have to exceed 12 kph for it to set the fault). The reason for this over pulling the ABS fuse, is that you still want the electronic brake distribution (EBD) to continue to function, so you won't lock up the rears before the fronts. If you do that correctly the ABS warning light will be on, and the red brake light will stay off. If you pull the fuse, I think the red brake light will be on also.

Why do I know all that? Maybe because I have been working on this stuff at Bosch since 1997. Maybe I have look at that algorithm so much that it is in my mind grapes. Seriously though, let me know if that works. I'm not 100% sure of what's in that controller, but I'm sure it's close.

Good luck!

993KT

Oh yeah, that's a good idea too. By killing the engine communication, ABD usually won't engage. I still think you have a wheel speed sensor fault, so eventually you will get the ABS light and red brake light.

If you car pulled to the right, then I think it's the rear left wheel speed sensor with the fault. The controller thinks your right wheel is spinning up, and tried to give it some brake. Go ahead and disconnect that faulty sensor in the short term.

bobt993

^^^^

I think your explanation sounds more like the root of the real problem. I had a similar issue on my race car which threw all sorts of fault codes in the ABS module. Right rear wheel was locking up continuously.

jackal2513

ok thanks, will do some testing tomorrow

souunds like if the abd and abs warning lights are on then the abd wont function in any case which is reassuring

if anyone has a picture of the correct pin i would be very grateful for a post of that

993KT

You can disconnect the wheel speed sensor at the wheel end. There is usually a 2 pin connector there.