Speedo Reads 3 MPH fast
 

The speedo reads 3 MPH fast on my 2002 S. Anyone else had same problem?? Since under warranty dealer should fix it.????

mike :)

Hi,

Are you on Stock Tire and Wheel Sizes? Are these Original to the Car? If not, the error may have been induced when switching sizes and failing to get the DME recalibrated. But, what are you referencing your speedo against? Are you sure the reference is accurate and not possibly the one with the error? Hope this helps...

Happy Motoring!... Jim'99

ya mine is about 4 mph slow, and I have stock wheels..The funny thing is if I hook my laptop into the obd the ECU shows the correct speed but the dash is off.
I dont know how true it is but I read somewhere that the acceptable tolerance is +/- 5mph which I thought was crazy for German engineering. But again I dont know how much truth is to that.

The dealer should be able to tweek it so it reads correctly. If that is something that is covered, that I don’t know I would say that it would be but if that crazy tolerance thing is true you might have to wheel and deal to get it fixed..

Hi,

You are correct, the Speedo readout adds what Porsche Calls a Safety Margin to the True speed.

If you own a '97-'00 Model, you can access the True Speed (in kph) through the Diagnostic Program Datastream hidden in your AC Climatronic Unit. It is C code 20c. This value is True Speed w/o the added Safety Margin. This code only updates once/sec. Hope this helps...

Happy Motoring!... Jim'99

My speedometer reads about 3-5 mph slow.

Yes stock wheels and tires, about 85% left. So there should be no error. Bascially to check the speedo use the paddle markers along the road driving at constant speed over the measured mile. Use the seconds over a mile divided into 3600 gives you the speed. Do this for a few miles and can get really close to speedo error if any.

mike

Hi,

This will give you a fair approximation, but so many variables can upset it and you're only looking for a 3MPH error. Failure to drive the Surveyor's Line on which the Mile Posts are established, Lane Changing or Lane Wandering, Tire Pressue and even Barometric Pressure (to a very slight degree) can all add up to some error.

I'm not disputing your speedo may be off, but I think if you want to really nail it, you're gonna need to have the Dealer get involved w/ the DME. I'd wait until you need to get him in there for something else and then have it corrected. Hope this helps... Jim'99

The other option, if you have one or have access to one, is to use GPS unit. That will give you a pretty accurate reading of your true speed. I use it so that I can set my cruise control to as close to the speedlimit tolerance level as possible :-)

The rest of the time, it ensure I don't get a speading ticket, even if I am slightly above the speedlimit. These Aussie cops have nothing else to do than raise revenue through speeding fines. Here in Melbourne the tolerance limit on urban roads is 3km/h. That's 2mph in normal speak - can you believe it! :eek:

While pulling a DTC code and watching the sensor readings to see what's up, I noticed something. Not something I would normally pay attention to, but I saw this thread earlier today so it sort of stuck out.

The car is idling in neutral, and what do I see? The 4mph safety margin Jim pointed out. The computer says the car is moving at 4mph, but it's sitting in the garage.

No wonder Porsche's look fast even when they're sitting still!! :dance: