DrewG

I have searched through multiple spoiler threads, but have yet to see anything quite like my situation. The spoiler on my red '91 C4 is completely functional. The spoiler light illuminates on the dash, and goes out when under way. The spoiler goes up at 50mph and back down when coming to a stop. The spoiler can be raised and lowered using the switch at the console. It works perfectly.

On my white '91 C4 the spoiler light does not illuminate on the dash. The spoiler does not go up at 50mph, nor 75mph. It can be raised and lowered using the switch on the console, and I can hear the relay clicking when it is fully erected or fully retracted. I checked fuse #37 and it has an intact 15amp fuse. In order to further diagnose the issue, I took the spoiler control module from under the dash in my fully functional red car, and installed it temporarily on the white car. Still no dice.

Based on the things that I have ruled out, I am thinking that the speed input info is not making it from the wheels speed sensor to the spoiler control module. I have heard that sometimes cars with alarms or aftermarket sound systems have spoiler issues, and I don't understand how those could be linked. My car has both (although I wish it didn't). I am not sure how to proceed.

Any help or recommendations are greatly appreciated. Thanks.

boxsey911

Seeing as you get the spoiler light on the clock in the red one but not the white one, I would start by trying the clock from the red car in the white car. A bad clock is well known to cause electrical gremlins.

DrewG

Thanks for the suggestion. I will try that and report back. Should I be able to just pull the gauge out from the front?

boxsey911

Yes. You might have to start it moving with a flat blade screwdriver and a cloth to protect the bezel. It will be very stiff if it hasn't been out for ages. You just have to keep working it out. The rubber gasket will most likely come out at the same time. The clock is the easiest one to get out.

DrewG

Hi Boxsey,

Thanks for the suggestion. The clock appears to be the issue. I have installed the clock from the red car in the white car and the spoiler light now illuminates. I haven't taken it for a drive yet, but that should be the confirmation. The clock that came out of my white car has a 993 p/n. It appears that the previous owner of the white car must have had an issue with the clock and tried swapping a newer one in. This now makes me nervous that there could be something upstream that is causing clock failure, but I won't know until I try it out for a bit. I wonder if there are any clock rebuild threads.

DrewG

Okay, so I have some news. The clock from the red car is now in the white car (I know that the spoiler works in the red car using this clock). The spoiler light comes on when the car is started, but does not go out when I start moving. I have checked the clock from the white car, and the previous owner decided that the solution to this problem was to remove the cluster bulb from that opening. This would imply that the speed information is not making it to the clock in my white 964. Does anybody have suggestions how to further diagnose?

Thanks,

Drew

boxsey911

Drew, at least that's some progress. The clock in mine is from a 993 (I replaced it myself) and works fine with the spoiler. It sounds like it's not getting a speed input, hence the light stays on and the spoiler will not work automatically. I believe that early cars get the speed signal from one of the front wheel sensors. However, if you've got a bad wheel sensor you would also get an ABS warning light so that may not be the issue. Hence why I'm hesitant to suggest trying swapping speed sensors between your 964s.

Have you had any ABS issues on the white one i.e. do you know if it works?

ras62

Try swapping R24 between cars and see if this solves the problem. It's the speed signal FCU.

boxsey911

Good call Rob. I was checking through Streather's trouble shooting pages last night and that relay was mentioned. So definitely worth checking out. However, all of the book's references to the spoiler not going out mentioned that the speedo would also not be working. Drew hasn't mentioned anything about the speedo?

ras62

Hi Steve, yes the speedo should not work if the FCU is faulty. Could be just a connection issue so worthwhile swapping them around and also checking the connection on the rear of the speedo itself. Failing this it looks like a wiring fault.

DrewG

Hi guys,

I have swapped R24 and also R51 (as it looks as though that relay is also related). Unsuccessful. The spoiler light stays on full time. The speedometer is working. When I get home from work, I will check the connection on the back of the speedometer.

I have also heard that aftermarket stereos and accessories can sometimes cause issues. My white vehicle has a small fob that can be removed below the steering wheel to prevent startup when leaving the car unattended. I don't know if it is an alarm per se, but I suppose it could be wired in to the speed sensor?
I am quite apprehensive to start digging into that wiring.

DrewG

I have not been in any situations where the ABS would activate, so that is another thing I will check out this evening.

ras62

If the connection at the speedo is ok then you need to check wiring continuity between the red/white wire on pin 2 at the speedo to the red/white wire on pin 12 at the spoiler control module.

JB 911

Sounds to me like someone did the boman spoiler mod to the white car, a popular 993 mod that takes away automatic control, but retains manual control similar to what you are stating. When you swapped the modules, that wouldn't make any difference. Open up the plug that plugs into the module and see if any wires are disconnected.

cxiaoga

There is a black wire connector under passenger side dash. Reconnecting it will solve the automatic spoiler raising and lowering problem. My 964 had the same issue before.