355 Speedo failed and suspension light on

Hi All

Today the speedometer in my 2.7 motronic 355 failed to work and I have the orange suspension warning light coming on.

Are they both connected in any way and what can I do for a fix?

Thanx

 

Probably a coincidence.

The speedo is driven by a sender that screws into the left side of the gearbox. It's a common failure.

Suspension light could be one of the shock actuators. There are threads discussing how to determine which one.
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Thanks for the reply

I think I read somewhere that a speedo failure can trip the suspension light...

Does anyone know if this is correct?

 

Yes it is, the suspension is speed sensitive driven from sensor output so when realises something is wrogn will light. correct the speedo and light will be resolved.

 

Thanku

Mad

 

You aré right. Mine failed and the light appears. Once you change the speed valvle you Will fix The problem.

Cheers

 

I just replaced my speedo sensor on my (1999) 5.2 F355 a couple of months ago.Must be a common failure item. I didn't get any failure light though. Not hard to replace.

 

Michael

To get at the sensor do u go in from underneath the car or from above?

Is it located under the drive shaft?

 

I wish I would have done a photo documentary of the procedure. I attacked from the bottom. I have ramps that I backed up on to get under the beast. Maybe some fellow F chat bros will chime in. I'm 99.99% sure that your sensor died. On a positive note, it'll keep your mileage down : ) Oh.....that's cheating...

 

http://ferrarichat.com/forum/showthread.php?t=330006

 

Thanku

I'll get at it soon

 

In addition to using speed inputs the suspension system also has sensors for g-forces (left/right and front/back), and gear selection. Pretty crazy system for it's time. Losing any one of those sensors triggers the suspension light and has the actuators freeze the suspension in the middle of the adjustment range until problems are resolved.

 

Wow

Thats pretty amazing

G force sensors

What do they do to the actual shock?

 

The G force sensors are looking for .3 G's front/rear or left/right. Depending on if they are seening that or less it changes what the computer is telling the shock actuators to do. The car has a preset pattern for either sport or normal suspension setting. Depending on the sensor inputs the actuators will adjust the actuators to the conditions. How it reacts will differ if you switch from sport to normal.

 

Just wanted to add, although likely to be the sensor, it could be the speedo itself. one problem I've had is a loose connection in the dash. The nuts can work loose. Found this out by replacing the sensor first and no change!

 

Mad

If it was the speedo itself then would i still get the check suspension light staying on?

 

Yes, it could, depending where would be the failure in the speedo. The suspension ECU is using an output of the speedo, as well as the Motronic and the F1 ECU if any, and not directly the sensor signal.
The speedo divides the frequency of the sensor by 2 before feeding the suspension, the Motronic and the F1.
So, a loose connector on the speedo could create those symptoms, but the most probable, and common, cause is the sensor.

 

Where is the gear sensor/switch? Or is that just on F1 models?

 

Complicated stuff

Thanks

 

I didn't realise your UK based. If you want I can try find my old sensor that was working and send it down for you to try that. Thats an easy first thing to try, as odds on as has been said.

 

Really too kind Mad but...I am in the south of spain

Thanks anyways.....how come u replaced the sensor if it works ok?

 

Not sure on that. I have never had to delve that far into it.

 

Process of elimination! Turned out speedo fault.

 

On a run into the Napa Wine Country this weekend, mine has developed the same problem. I did notice the speedo come back on eratically, but now seems fully off. We hit a thunderstorm on Wed night, so I thought everything getting wet might have had something to do with this? Also, the suspension error light would only come ON on the next ignition key cycle after the speedo would quit. Mine's a '95 F355. I'll have a look at the speedo first, and then replace the sensor if everything looks good there. Will keep the list posted.

 

I bet it's the sender. It looked like it's not too hard to change. Just had my guys do this and car works perfectly, and suspension light is now off.