1993 964 C4 speedometer malfunction
09-07-2006, 01:17 PM
#1
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1993 964 C4 speedometer malfunction
Hello everybody,
My otherwise utterly reliable and trustworthy 1993 964 C4 developed some annoying symptoms this afternoon. The speedometer stopped working, the ABS, locking differential and rear spoiler warning lamps came on and that was accompanied by an annoying warning beep.
From what I gather from information on Rennlist and from other online sources, it is either the electronic signal conversion box (part number 964 618 221 00) or the reed switch at the front left wheel.
I called the local Porsche dealership. None of the parts are in stock. They need to be specially ordered. As a result, I cannot return either of those parts.
Is there a way I can tell for sure which part is to blame for this problem? As additional information I should mention that the warning lights and beep come on the moment I start the engine. The car does not need to be moved at all.
Thanks for the feedback
Rik Gruwez
Brugge, Belgium
My otherwise utterly reliable and trustworthy 1993 964 C4 developed some annoying symptoms this afternoon. The speedometer stopped working, the ABS, locking differential and rear spoiler warning lamps came on and that was accompanied by an annoying warning beep.
From what I gather from information on Rennlist and from other online sources, it is either the electronic signal conversion box (part number 964 618 221 00) or the reed switch at the front left wheel.
I called the local Porsche dealership. None of the parts are in stock. They need to be specially ordered. As a result, I cannot return either of those parts.
Is there a way I can tell for sure which part is to blame for this problem? As additional information I should mention that the warning lights and beep come on the moment I start the engine. The car does not need to be moved at all.
Thanks for the feedback
Rik Gruwez
Brugge, Belgium
09-07-2006, 09:34 PM
#2
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First start by fully charging the battery... test again and if the problem is still there your diagnostic of the electronic signal conversion box might be correct.
I am positive others will chime in.
Edit: After searching on the topic... Replacing the sender should solve the problem. Let us know!
I am positive others will chime in.
Edit: After searching on the topic... Replacing the sender should solve the problem. Let us know!
Last edited by Wachuko; 09-07-2006 at 09:57 PM.
09-07-2006, 10:50 PM
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Does the car run ok ,, or is it missing or has it lost power:
I had a bad coil that created voltage leak and my dash lit up abs lights came on and the beep occured.
Replaced coil and a few bad plug wires and solved my problem.
But I did not have any issue with the speedometer so it may not be relevant in your case.
Good luck!!
Bob
I had a bad coil that created voltage leak and my dash lit up abs lights came on and the beep occured.
Replaced coil and a few bad plug wires and solved my problem.
But I did not have any issue with the speedometer so it may not be relevant in your case.
Good luck!!
Bob
09-07-2006, 11:18 PM
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I had the exact same symptoms (except for the beeping) on my previous 89 C4. Fixed it under warranty. It was either an ABS sensor or sender but it was definatley ABS related with my C4. Good luck
09-08-2006, 03:02 AM
#5
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Originally Posted by GRUWEZ
Is there a way I can tell for sure which part is to blame for this problem? As additional information I should mention that the warning lights and beep come on the moment I start the engine.
09-08-2006, 04:47 AM
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If you read the post the key information is that the warning lights come on the instant the engine is started. This immediately tells me that there is no power to the PDAS/ABS control unit (I PMed the poster yesterday with what to check). This is becoming a common problem here in Europe and it has happened to me twice. It has happened in the USA as well. We nicknamed this the "dissolving pin syndrome" in 1999.
The wheel speed sensors are not tested by the system when the engine is started. They will be checked the instant you move. Why? Because they are self generating units therefore they have no output until the wheels are turning.
The first thing to check of course if everything else is running properly. Based on the post I do not see other problems reported except those directly related to the opration of the control unit. Under or overvoltage failures usually manifest themselves in other ways apart from just firing up PDAS and ABS warning lights. The key is the ABS warning light. In the C4 bad batteries screw around with PDAS and the hydraulic boost pump setting off the beeper, but after a time not instantly. However the ABS warning light usually remains out.
If you have this problem the first thing to do is check fuse no. 16. This provides the power to the system. The next thing to check is the ABS relay R34 which switches power and controls the under and over voltage levels.
Unfortunately in the overwhelming cases that I have investigated including my own, the problem has been corrosion in the connector on the PDAS/ABS control unit. Once started it is almost impossible to control and repair especially if you drive in winter on salted snow.
The really hard part is advising people to remove the connector because if the power pins are corroded they will often come off with the connector and then you are in trouble.
This problem will usually first manifiest whilst you are driving. Maybe going over bump or when it's wet. This is saying that power has been removed, but obviously at this time the problem could be anything because it appears to be a dynamic problem.
Eventually if the problem is in the power circuit the warning lights come on as soon as you start indicating that power is not reaching the control unit at all. This is what I designate a static problem.
Jason is correct when he says the system is diagnosable with the Hammer when either the PDAS and or ABS warning lights are on, but the easiest way to check is to do the easy things first and check the fuse. Then the relay (which is not easy to check) then remove the conector and check for corrosion.
Components such as the ABS sensors can be checked with a multimeter for resistance and their output can be checked with an Oscilloscope.
Getting back to the posted problem, one always hopes it is something else, but personal experience in the European environment usually ends up with corrosion causing the problem.
The design of the PDAS/ABS control unit connector, its location and the fact that if the luggage compartment seals are worn of damaged, water can easily enter and collect around the connector itself. Maintenance of these seals is critical especially when driving in the wet or in winter in the snow and salt. I also recommend that you try and protect the control unit against water ingress.
Never change anything until you can confirm it failed especially nowadays when shotgunning is very expensive with Porsche upping their prices by 300% on some 964 parts nearly two years ago.
Ciao,
Adrian.
The wheel speed sensors are not tested by the system when the engine is started. They will be checked the instant you move. Why? Because they are self generating units therefore they have no output until the wheels are turning.
The first thing to check of course if everything else is running properly. Based on the post I do not see other problems reported except those directly related to the opration of the control unit. Under or overvoltage failures usually manifest themselves in other ways apart from just firing up PDAS and ABS warning lights. The key is the ABS warning light. In the C4 bad batteries screw around with PDAS and the hydraulic boost pump setting off the beeper, but after a time not instantly. However the ABS warning light usually remains out.
If you have this problem the first thing to do is check fuse no. 16. This provides the power to the system. The next thing to check is the ABS relay R34 which switches power and controls the under and over voltage levels.
Unfortunately in the overwhelming cases that I have investigated including my own, the problem has been corrosion in the connector on the PDAS/ABS control unit. Once started it is almost impossible to control and repair especially if you drive in winter on salted snow.
The really hard part is advising people to remove the connector because if the power pins are corroded they will often come off with the connector and then you are in trouble.
This problem will usually first manifiest whilst you are driving. Maybe going over bump or when it's wet. This is saying that power has been removed, but obviously at this time the problem could be anything because it appears to be a dynamic problem.
Eventually if the problem is in the power circuit the warning lights come on as soon as you start indicating that power is not reaching the control unit at all. This is what I designate a static problem.
Jason is correct when he says the system is diagnosable with the Hammer when either the PDAS and or ABS warning lights are on, but the easiest way to check is to do the easy things first and check the fuse. Then the relay (which is not easy to check) then remove the conector and check for corrosion.
Components such as the ABS sensors can be checked with a multimeter for resistance and their output can be checked with an Oscilloscope.
Getting back to the posted problem, one always hopes it is something else, but personal experience in the European environment usually ends up with corrosion causing the problem.
The design of the PDAS/ABS control unit connector, its location and the fact that if the luggage compartment seals are worn of damaged, water can easily enter and collect around the connector itself. Maintenance of these seals is critical especially when driving in the wet or in winter in the snow and salt. I also recommend that you try and protect the control unit against water ingress.
Never change anything until you can confirm it failed especially nowadays when shotgunning is very expensive with Porsche upping their prices by 300% on some 964 parts nearly two years ago.
Ciao,
Adrian.
09-08-2006, 05:19 AM
#7
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Originally Posted by Adrian
This is becoming a common problem here in Europe and it has happened to me twice.
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09-08-2006, 05:32 AM
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Jason,
Its the PDAS/ABS control unit with the 55-pin connector. To answer your question, tried and failed. It's actually 2-pins that go not just one and well Bosch did not make it easy to do. I gave up when I had to try and desolder the flexible connector strip from the bottom of the pins. If I had access to my former place of work I might have been more successful with specialist equipment which I do not have at home.
I actually sold my 964 without the control unit and discounted the selling price accordingly.
Ciao,
Adrian.
PS: I actually took the unit to two facilities here in Switzerland who claimed to repair such things. Both decided they could not do it either. Replacing the pins in the car side connector is a sod of a job as well, but this is achievable.
Its the PDAS/ABS control unit with the 55-pin connector. To answer your question, tried and failed. It's actually 2-pins that go not just one and well Bosch did not make it easy to do. I gave up when I had to try and desolder the flexible connector strip from the bottom of the pins. If I had access to my former place of work I might have been more successful with specialist equipment which I do not have at home.
I actually sold my 964 without the control unit and discounted the selling price accordingly.
Ciao,
Adrian.
PS: I actually took the unit to two facilities here in Switzerland who claimed to repair such things. Both decided they could not do it either. Replacing the pins in the car side connector is a sod of a job as well, but this is achievable.
