[vroecker]

I have an intermittent problem where the attention light for the ABS comes on. When this first happened, I had the master brake cylinder replaced, however that didn't fix the problem with the attention light, which comes on and then, after a short while (1-2 miles), goes off by itself. The mysterious thing about this is that when the light comes on, the speedometer drops to zero. When the light goes off, the speedometer starts working again. It seems to happen more when the car is cold. My mechanic says he had the same thing happen in his BMW and it could be one of two things. The dealer doesn't know what it is, and thinks that replacing the instrument board might fix it, for $1400. Any ideas?

Partial Post: Please Login or Register to read the full post.

[flash]

sounds like a problem at the sensor at the wheel - i believe the left front wheel has the speed sensor

Partial Post: Please Login or Register to read the full post.

[Anchorman]

Don't you just love the way some dealers go about "fixing" problems? Like this case..."We have no idea what the cause is, so let's do something expensive and see what happens." Ask them if they'll do the instrument board free of charge if replacing it doesn't fix the problem.

I think Flash is pointing you in the right direction.

Partial Post: Please Login or Register to read the full post.

[vroecker]

Thanks. I don't work on the car, so I have no idea where the speed sensor is - I guess it's used by the speedometer. But why would it affect the ABS light?

Partial Post: Please Login or Register to read the full post.

[flash]

i think they might share something - the fact that both things are wigging out simultaneously is what leads me there

i'm only going on blurry memory as to which wheel the speed sensor is on - a quick look at the wiring diagram will tell you though

i suppose it could be a fuse or relay in common too - again, i would have to look at the wiring diagram to know

either way, likely not an expensive fix

Partial Post: Please Login or Register to read the full post.

[firefish]

<!--quoteo(post=78171:date=Aug 19 2009, 02:33 AM:name=vroecker)-->QUOTE (vroecker @ Aug 19 2009, 02:33 AM) <{POST_SNAPBACK}><!--quotec-->The mysterious thing about this is that when the light comes on, the speedometer drops to zero. When the light goes off, the speedometer starts working again. Any ideas?<!--QuoteEnd--><!--QuoteEEnd-->

My guess is that the speedo/ABS quits and then the '!' light goes on, not vice versa. This sounds like a wiring problem. There is a good chance that ABS sensor and speedo wire are routed the same way so I would start at the wheel checking the wiring thoroughly. Might just be a bad connector and the wheel well is a pretty harsh environment so it is most likely that you will find the problem in that end.

Partial Post: Please Login or Register to read the full post.

[vroecker]

Where would I find the wiring diagram?

Partial Post: Please Login or Register to read the full post.

[flash]

workshop manual - a detailed search here will turn up a link

Partial Post: Please Login or Register to read the full post.

[jfrahm]

Unlike the 944, the 968 gets it's speedo signal from the ABS controller, which gets it from a wheel sensor. It is possible

Generally the wheel sensor wiring goes bad as the wiring from the car body to the hub is subject to a lot of wear and damage. It is also possible the ABS module is having problems, if it goes out you would also lose this speed signal.

The wheel sensor and reluctor ring in the hub can be cleaned, that sometimes helps. This ring and pickup arrangement sends an AC voltage signal to the ABS controller to indicate the wheel speed. It is possible to connect a DMM to the ABS controller inputs for each wheel and look for this voltage, and even leave the meter hooked up in the car to see if it goes to zero when you lose the speedo. The voltage is generated by the wheel and will still be there even if the ABS controller is not working. However if the wiring is in bad shape you will see that voltage go away when the circuit opens up.

If the problem happens when you hit a bump, that's a clue it's the wiring. I suppose it could also be a bad ground to the ABS controller or something, but particularly if you hit a bump with one particular wheel and that causes it, you are on to something.

If you like, you can try wrapping the lower part of the wire to the sensor with a stiff wire and some tape to act as a strain relief and see if that makes the problem better. If so you have a bad connection right at the wheel sensor. While you are at that you can easily check the other connections in the harness by the connection for the brake pad wear sensor.

Happily this part is only $70-$125 and even seems to be available at Autozone, I needed one for my Saab and it was like $350 so I got a used one, and used electrical wear parts make me feel icky.

-Joel.

Partial Post: Please Login or Register to read the full post.

[firefish]

<!--quoteo(post=78397:date=Aug 22 2009, 12:55 AM:name=jfrahm)-->QUOTE (jfrahm @ Aug 22 2009, 12:55 AM) <{POST_SNAPBACK}><!--quotec-->Unlike the 944, the 968 gets it's speedo signal from the ABS controller, which gets it from a wheel sensor. It is possible

Generally the wheel sensor wiring goes bad as the wiring from the car body to the hub is subject to a lot of wear and damage. It is also possible the ABS module is having problems, if it goes out you would also lose this speed signal.

The wheel sensor and reluctor ring in the hub can be cleaned, that sometimes helps. This ring and pickup arrangement sends an AC voltage signal to the ABS controller to indicate the wheel speed. It is possible to connect a DMM to the ABS controller inputs for each wheel and look for this voltage, and even leave the meter hooked up in the car to see if it goes to zero when you lose the speedo. The voltage is generated by the wheel and will still be there even if the ABS controller is not working. However if the wiring is in bad shape you will see that voltage go away when the circuit opens up.

If the problem happens when you hit a bump, that's a clue it's the wiring. I suppose it could also be a bad ground to the ABS controller or something, but particularly if you hit a bump with one particular wheel and that causes it, you are on to something.

If you like, you can try wrapping the lower part of the wire to the sensor with a stiff wire and some tape to act as a strain relief and see if that makes the problem better. If so you have a bad connection right at the wheel sensor. While you are at that you can easily check the other connections in the harness by the connection for the brake pad wear sensor.

Happily this part is only $70-$125 and even seems to be available at Autozone, I needed one for my Saab and it was like $350 so I got a used one, and used electrical wear parts make me feel icky.

-Joel.<!--QuoteEnd--><!--QuoteEEnd-->

Does the speedo get input from all four corners or is it disabled regardless of where the problem is as a sensor problem will shut down the ABS-unit and thus disable the speedo? Will the speedo always fail if the there is a problem with the ABS-unit. That would seem like a poor construction to me.
.

Partial Post: Please Login or Register to read the full post.

[jfrahm]

<!--quoteo(post=78412:date=Aug 22 2009, 12:51 AM:name=firefish)-->QUOTE (firefish @ Aug 22 2009, 12:51 AM) <{POST_SNAPBACK}><!--quotec-->Does the speedo get input from all four corners or is it disabled regardless of where the problem is as a sensor problem will shut down the ABS-unit and thus disable the speedo? Will the speedo always fail if the there is a problem with the ABS-unit. That would seem like a poor construction to me.
.<!--QuoteEnd--><!--QuoteEEnd-->


I think the speedo signal is only taken from the LF wheel. I am not sure if disabling the ABS controller will take out the speedo signal, maybe it is just a passthrough and the signal is still there if you pull the ABS fuses, relays, etc. Never tried it. However I read a post on RL about getting a speedo signal for a 944 Turbo with a swapped-in 968 6 speed, and they were using a 968 ABS controller to get the ABS to cluster signal. That seems strange to me but I guess it'd be one way to solve the problem, put a signal converter in the ABS controller that outputs a signal like the old speed sensor in the 944 transmission, then send that to the cluster. That way you do not need to revise the cluster (but they did that anyway, the speedos are different.)

I'm just trying to be through, odds are it's a wheel sensor wiring issue.

-Joel.

Partial Post: Please Login or Register to read the full post.

[firefish]

<!--quoteo(post=78514:date=Aug 24 2009, 12:49 AM:name=jfrahm)-->QUOTE (jfrahm @ Aug 24 2009, 12:49 AM) <{POST_SNAPBACK}><!--quotec-->I think the speedo signal is only taken from the LF wheel. I am not sure if disabling the ABS controller will take out the speedo signal, maybe it is just a passthrough and the signal is still there if you pull the ABS fuses, relays, etc. Never tried it. However I read a post on RL about getting a speedo signal for a 944 Turbo with a swapped-in 968 6 speed, and they were using a 968 ABS controller to get the ABS to cluster signal. That seems strange to me but I guess it'd be one way to solve the problem, put a signal converter in the ABS controller that outputs a signal like the old speed sensor in the 944 transmission, then send that to the cluster. That way you do not need to revise the cluster (but they did that anyway, the speedos are different.)

I'm just trying to be through, odds are it's a wheel sensor wiring issue.

-Joel.<!--QuoteEnd--><!--QuoteEEnd-->

So the main suspect should be the LF wiring as a problem with the other three would risable the ABS but not the speedo.

Partial Post: Please Login or Register to read the full post.

[Lim Yong]

Hi all,
Here is my current problem. after replacing pads. the pad light comes on but only after i am under way. Then the abs lights starts to light up, again after I am underway. I just now notice that the speedo gauge needle drops when I go over bumps.

I thought it was the struts are back so I order replacements form Paragon. Also had the odometer gear problem so I ordered the 15 tooth gear from Odometer gear. I took out the instrument cluster to check the gear and then realized that I can drive without it, I have no AC. so I put the cluster back in the car and now have AC. now the left temp/fuel gauge is not functional, but the brake pad light still comes on.....So..what the"""".

will check the temp/fuel gauge connecter tommorow. Any suggestion are welcome.
thanks

Partial Post: Please Login or Register to read the full post.

[flash]

check the connectors at the back of the cluster - if they are at all loose or improperly seated, weird things happen - this happens a lot when the little locking ears are broken

Partial Post: Please Login or Register to read the full post.

[unknown4u]

I had the same symptoms, After investigation it was a culprit relay. After 18 years it was burnt. Check it first because I had the same symptoms. Speedo drops and abs light goes on. It the realy works again if you hit a bump than the speedo goes up and the light out. vice versa.

Simpel fix, hard to find because the relay because you dont can simulate a bumpy road when standing still and measure it all.

Good luck.

Partial Post: Please Login or Register to read the full post.

[Lim Yong]

update,
ordered the ABS relay from sunset.
Also, per flash I reconnected the electrical plugs..now the fuel gauge is acting funny and the brake pads light
still stays on after starting the car. I did install the odometer gear and so now have that working..

Rats, now the airbag light is on. Forgot that I should not turn ignition on without the console plus in....Oh well

Partial Post: Please Login or Register to read the full post.

[Lim Yong]

Ok, update......
replaced the relay and that didn't stop the ABS light on and speedo drop over bumpy roads problem..having the struts replaced now by a specialist.
will look at the ground wiring once i get the car back....

Partial Post: Please Login or Register to read the full post.

[vroecker]

It's been a long time, but other things took priority, like finding a job.... Anyway, finally took the car in to be diagnosed and try various things. It turns out there were two separate problems. The speedo problem was a bad instrument cluster circuit board, which apparently is fairly common in 968s, 944s, 924s, and 928s - the speedo people recognized the problem right away, and my mechanic said he knew it was a problem but there were other things it could be so he didn't want to commit. The speedo people replaced a couple of parts that could have been the problem (capacitors, I think) but that didn't fix it. Replacement circuit boards have to come from Germany, but my mechanic found a replacement cluster from a parts supply house. The odometer on the replacement didn't work so I sent it to the speedo people (I'm on a first name basis with them now) to replace the two broken gears - $125 plus shipping. The ABS light was still coming on, which it turns out was a bad relay. The used cluster was $375 and the relay was $104. Not to mention the speedo sensor ordered from Germany that turned out not to fix the problem, but had to be tried first in case it did fix things. While the cluster was out of the car I tried driving it a little - turns out the battery doesn't charge when the cluster isn't there and the car ran out of electricity and had to be towed. So - bad circuit board and bad ABS relay. But it's finally fixed!

Partial Post: Please Login or Register to read the full post.

[Lim Yong]

Thanks for following up.....Is the speedo sensor for the LF wheel? I still have htis problem and I replaced the ABS Relay with no luck

Partial Post: Please Login or Register to read the full post.