1990 964 C2 rear spoiler light & speedo

[johnhedge]

Hi list,

This is my first post, I hope you can help.

The rear spoiler light stays on after a cold start and the speedo doesn't work. The rear spoiler wont raise either at 50+ mph.

Once the car gets warm everything starts to work as it should, light goes out, speedo works and spoiler raises.

TIA

John

[Don Plumley]

Hi John - welcome.

I think the coincidence between the speedo not working and the spoiler working when the speedo starts working is a connection.

The spoiler needs a speed signal to raise. So when the speedo finally gets a signal to start working, then the spoiler knows when to raise and lower.

The speedometer gets it's signal via the ABS wheel speed sensor, once the signal is converted by the pulse sender. I found this:

The ABS control unit receives wheel speed information from sensors at each of the four wheels. Among the many inputs and outputs from the ABS, Pin 17 provides a signal to Pin 6 on the FCU or Frequency Converter Unit, also known as G16, located in the Central Electrics (AKA main fuse box). FCU Pin 5 is the output signal to the speedometer. Pins 2 and 7 are power and ground respectively.

So, I'd check the ABS Fuse (any other warning lights?), the ABS Wheel Sensor, and the Pulse Sender (FCU).

[johnhedge]

Thanks for the very detailed response, Don. I'll check it out and let you know how it goes.

Best wishes,

John

[computamedic]

This is a classic symptom of the "famous" clock problem. The time of day clock has a lot of internal circuitry that has an impact on many. many circuits around the car - the speedo included. The clock circuitry suffers badly from cold solder joints and re-soldering them will generally solve all such problems.

Dismantling the back of the clock is fairly straight-forward but does require the use of a soldering iron and a solder sucker. Once apart, the inside surface of the printed circuit board needs all of the joints re-soldered.

Incidentally, the early cars (up to 1991) used a speed transducer in the transmission to generate the speed signal to the speedo and spoiler control unit. The later cars (post 1991) used the ABS wheel sensor signal via a frequency converter in the fuse box to generate the necessary signal.

Regards

Dave

[Don Plumley]

Thanks for the details and correction Dave.

Don