Hi all

My "new" (well, new for me, less than 1 month old!) 1990 964 C4 has suddenly developed a glitch. After starting one morning, the speedometer, odometer and spoiler all failed to work. The spoiler warning light came on the dash after starting, and I didn't know what to make of it. After accelerating to the required speed for self raising, nada, nothing, it stayed down. I tried a few more times and probably reached 80mph just to make sure I finally realised that the speedo must somehow be linked to the spoiler, and is the "trigger" that raises the spoiler. Anyway, I could still raise and lower the spoiler manually with the console mounted control. I started worrying about expensive repairs, but an hour later, back to normal. This happened once again 2 days later (with the wife in the car who I had promised that the Porsche was more reliable than the 30 year Ferrari Dino I nearly bought - very embarassing ).

Since then, which was about 4 days ago, same thing happens nearly every time whenever I start car, spoiler warning light comes on, and usually disappears after I have started moving, maybe 100 yards down the road or usually within 1-2 minutes of starting. Is this something that will get worse? Is the speedo "cable" loose? Is it all electronic?

Although speedo not working would not be considered a "show stopper" by some, here in radar crazy, speed limit obsessed Oz, very easy to creep over the limit if I only use tacho as a guide.

Any ideas or suggestions? I could take to a Porsche specialist, but not sure if they will be able to analyze due to the random, intermittent nature of problem.

Have done a search on Rennlist Forums, but doesn't appear to be a common problem.

 

Check your fuses, then check for fault codes. Do a search here on the DIY, it isn't too difficult. If it was a loose connection to the spoiler it wouldn't work at all.

 

the light stays on until you hit 5mph or so after start up. Thats normal for the spoiler light.

 

Thanks for the prompt reply Gary R. If it was a blown fuse, I assume it would not be intermittent, so I assume I am looking for a "loose" fuse"?

Excuse my ignorance, but how do I look up "fault codes"???

 

Thanks Jim. That makes sense, explains a lot, but still leaves me with 2 "events" where everything stopped working.

 

I have a sneaking feeling that this is not unrelated to the common problem of the dry joint connections on the back of the clock. I'm not sure why but I know my car suffered the same problem on a number of occasions - until I fixed the clock - and it's never happened again since. There are several threads on the subject if you search.

Regards

Dave

 

On the C2 there is an electrical pulse sending unit on the side of the transmission, 964 speedo & odo are electrically driven rather than by a twisting cable.

I had a similar problem several years ago w/my '90 C2, best I could tell, signals were not making it from the sending unit on the side of the transmission - I got under the car, pulled off the electrical connector to the sending unit and cleaned and greased the connection (e.g., dielectric grease to prevent electrical connections from corroding/oxidizing), plugged it back in and all was well. That signal drives/enables all three systems you mentioned. As I recall it was on the right side of the C2(manual) transmission case.

I seem to recall that the C4 is slightly different in this respect, but I don't remember details.

Edit: there was another symptom when my odo and speedo were out, namely that the spoiler would come up automatically at freeway speed (60mph+?) but would not later come down automatically. Had to use the manual switch on the console to retract it. This leads me to believe that there is a fail safe system or secondary signal source to activate the spoiler at higher speeds, perhaps using information from the ABS system. Well, yours did not do this, which may suggest subtle differences between C2, C4.

But if you can find the sending unit, checking its electrical connection would be a good first troubleshooting step.

 

Johnmetro

I had this a couple of times last year when I had the seats out and put them back in again.

Made sure all the connections under the drivers seat and never had it again.
The seats were the only things that I had touched so figured that I'd dislodged something under there.

Rob

 

Hmmmm, seats. It first happened after leaving Baby Kingdom last Saturday. I had been trying out some baby seats to fit (Safe and Sound, Compaq fits and was crawling in and out, and had moved the front seats ALL the way forward, folded down, and inside out, so I had some crawl space to get in and out with seats while fitting. It's a stretch, but food for thought. I will have a little "poke around" and see if anything amiss.

I can just see the conversation at Porsche specialist...

Mechanic: "What did you do"
Me: "Nothing"
Mechanic: "What did you touch"
Me: "Honest, I didn't touch anything"
well... maybe just a little....

 

See this thread , e.g. post #14

See also post #14 in this thread

[Search term query was "signal and (speedo or odometer)"]

 

I had the same thing, although intermittent - all cured with a new clock (but oddly for a different reason!). I'd look for dry joints on the connections there first (and it's the easiest one to get out of the dash!).
Good luck.