TheM@x

Hi,

this e-mail I have send to Adrian, but I hope others can help me too:

I have red al the articles here about the speedo and ABS warning light problems.

I own a 964 C2 Cabrio Tiptronic from 1990.

In the morning when I drive away, now and then the spoilersignal keeps burning, the speedo is not functioning and after aprox 10 meters driving the ABS light turns on, together with the beep sound.

As you have wrote, on a '90 model the speedsensor is on the transmision, on a '91 it's via the ABS by the left front wheel sensor.

My dealer has noticed (not sure) that indead the speedsignal on my '90 was by the ABS's left wheel sensor.
Also after he checked the sensor, is had a different value then the others.

He replaced the left sensor and the problem was gone......for two days ........ Till yesterday, the same problem did occur, after I drove it for half an our, went saling, came back and started the engine again. Grrrrr... <img border="0" alt="[grrrrrrr]" title="" src="graemlins/cussing.gif" /> .. ABS........

Can you help me

Can it be indead a sensor on the transmission, where is that sensor, or are they the same as on the frontwheel, but then on the backwheels ?

Is it possible that my '90 model indead uses the ABS for the speedsignal by the sensors on the frontwheels ?

Pleas help me out, before I go back to my dealer.

Like to hear from you.

Regards,
Max - Holland

Adrian

Dear Max,
What is the 10th digit of your VIN. If it is L then you have a 1990 model and I think you need to find another mechanic. One that can read a wiring diagram. If the 10th digit is a M then it is a 1991 model. Make sureplease that you are giving the model year and not the year of manufacture.
No it is not possible that if you have a 1990 C2 tip that it uses the ABS wheel speed sensor unless the whole 964 has been modified with a new harness.
The ABS issue and the spoiler issue may well not be directly related. This is looking like a wiring harness problem.
For the record it is quite normal for the wheel speed sensors to be different when measured for continuity.
However I think you need to tell me what actual model year you have. If you have a real 91 model then I feel you have a wheel speed sensor problem. Does the rear spoiler open?
Ciao,
Adrian
911C4

Adrian

An update for you Max.
I might have been a little harsh on your mechanic because I can see now how this mistake can be made. I have consulted my Tiptronic manual as well to be sure.
For a 1990 model year the drive speed (speedo) is provided by the pulse sender mounted int he transmission. It is mounted on the left side from the drivers seat position.
Now there is a little complication which I can see causing confusion.
The Tiptronic electronic control unit has to calculate longitudinal and lateral acceleration. Lateral is via an accelerometer. Longitudinal is via the wheel speed signal input from the ABS control unit. ALL four speed sensors provide this information (averaged) not the myth of the front left. The tip control unit calculates wheel speed accelerations to obtain vehicle acceleration. The C2 ABS control unit calculates the same internally.
So your speedo is getting inputs from the pulse sender and from the tiptronic control unit.
Now the tiptronic control unit cannot use raw data from the ABS. The data has to be converted. The tip is fitted with a frequency converter assembly for this purpose. 1991 and up C2s, C4s and Turbos also have a similar device installed.
Now you have not reported any transmission problems so I have to assume that your ABS output to the tip control unit is okay.
You still need to answer my question on your actual model year of tip.
Ciao,
Adrian
911C4

TheM@x

Hi Adrian,

thanx for your reply, I will check when I am at home.

Answer to your first question, the spoiler light keeps burning together with a not functional speedo, so I think the spoiler does not come up.

After I drive while, the spoiler light goes out, spoiler comes up and the speedo is getting signal.

When I restart the car after that, the ABS, speedo and spoiler problem is gone.

(p.s. the problem is not always occuring)

Mostly till the next morning.

I'll keep you posted.

Regards,
Max

TheM@x

Hi Adrian,

hereby the VIN-number:
WP0ZZZ96ZLS422984

I know that my speedo has two green wires to the speedo pin in the multiconnector. That's where I get my signal for my gps-navigation system.

Hope you can help, monday the car goes back to the mechanic.

regards.
Max

Adrian

Dear Max,
You have a 1990 model year tip. This means that under normal as delivered status, your speed signal is from the pulse sender mounted in the transmission. As per the description in the manual. However you have thrown a curved ball. You have a GPS fitted. I have no idea how this is wired in. It could have all been rewired to suit the requirements of the GPS. I have seen this once before.

Summary:
Speedo input is from the pulse sender
ABS signal is supplied to the tiptronic control unit.
Failed speedo would cause the problem.
Failed speed sensor would cause your speedo problem.
Failed speedo sensor will cause the spoiler warn to fail.
Failed speedo will cause the spoiler warn to fail.
ABS speed sensor failure will cause the ABS light to come on.
Right rear only ABS speed sensor failure will cause a rear spoiler failure.

The only thing I could think that they all might have in common is the frequency converter relay.
Sorry I cannot help you anymore but unless I have the data on the GPS installation there is little more I can do.
Ciao,
Adrian
911C4

TheM@x

Hi,

The GPS is a Blaupunkt RNS149 (later installed), I just needed a speedsignal, I looked at the wirescheme and found the green one. I don't think it has to do with the problem. The GPS works fine (if the speedo does , it is not attched at the moment and I still have the problem.

ok, conclusion, there should be a pulse sender on the transmission, so we have to find that one.
I also have to find the frequency converter relay, I haven't seen one yet.
The tiptronic is working ok.
It can be the speedo.
It can be one or more speed sensors.

At least I have more info now, thanx!!!

Regards,
Max

TheM@x

Adrian, still a question.

Isn't it logic that there should be a connection between, the not functional speedo, the spoiler light and the ABS alarm ?

Because if sometimes in the morning my speedo is working, the spoiler light goes out and there is no ABS alarm.

There should be a connectione, but when I read your last mail, you suggest three differen errors. Wich one should likely be the problem ?
Can it be the ABS controller ? ($1500,- )

Adrian

Dear Max,
The ABS uses wheel speed sensors, the spoiler raising and lowering is done by wheel speed sensor input. The speedo uses a separate input source as does the spoiler warning system.
The only item which I could see causing you a problem in this area would be the rear spoiler control unit (under the right seat on a 1990 model). If it is failing it might be dragging the speedo and abs control unit signal outputs down.
The ABS control unit feeds the tiptronic so if there is a problem your tip would also be incorrectly functioning. I am assuming of course that you do know how the tiptronic is supposed to work and when it changes gears up and down. Check your owners manual and make sure the tip is working correctly.
All I can suggest is you pull the connector off the rear spoiler control unit and see what happens. The speedo I would have suspected first but seeing as the speedo has nothing to do with the ABS on the 1990 models I find it unlikely but I suppose anything is possible. Did you have the problem before or after you hooked up the GPS. If after, I would disconnect the GPS and see what happens.
Ciao,
Adrian
911C4

TheM@x

ok,

the problem is fixed, at least I hope , the two fron speed sensors where defect, de connection of the two rear sensors was terrible.

The bleu frequenty converter was defect too.

So there was more then one problem, the ABS did after all nothing to do with the speedo.

Thanx for all the advise, i think my mechanic did a good job.

Regards,
Max