Odometer Mileage Incorrect?

[Sooty Si 1]

Hi all,

 

Was messing around last night with the AlfaOBD Android app, and it showed that the car's mileage (according to the ECU?) is around 126000 km. That works out to around 78750 miles. The odometer in the dash reads 84717 at the moment. I seem to remember the same scenario when I last plugged her into MultiEcuScan. Could the ECU have failed and been replaced after only 6 or 7 k, or is there another reason for the error? I don't know if the two are independant or if the speedo get its readout from the ECU. If the ECU / speedo had failed, at that point the car would still have been under warranty, right? So you'd think Alfa would have corrected the figures, perhaps, if thats possible?

 

Another possibly related snag is the infocenter displaying mpg in km/l, which, I've been led to believe, can be cured by fitting a new speedo. So, if I were to do that, (not likely, as I don't give a fuck about mpg and a new unit would probably cost a small fortune), would the mileage on the new speedo update to the car's actual mileage, or is that something only Alfa could do?

 

Sorry if it all sounds a bit garbled and twisted, I'm on the last night of my weeks' nightshift and am feeling the strain a little.

[Smaky 73]

First of all I wouldn't worry, all cars which use the ABS to generate the speed signal suffer this error.

 

The ABS is used to calculate the speed signal in Km/h based on a fixed wheel diameter figure and this is what you see on the speedo, the way the guage is marked up has no effect on this as it's purely a low voltage signal to excite the electromagnet around the base of the needle. This is the figure the Engine ECU will give you, although it's marked up as Miles on the diags, it is in fact the Km reading (12600). This reading excludes reverse.

 

The Speedo head takes this figure and has an additional calculation which comensates for the RPM against fixed wheel diameter, this gives you the other number (84717), as in if your tyres where the OEM 16" ones and ran the correct pressure with no wear in a straight line, this is the distance you would have covered, including in reverse.

 

And by comparison your discrency is pretty average, 9% isn't bad, I've seen well inexcess of 15% before.

[Sooty Si 1]

Thanks Smaky, for that illuminating and highly informative reply. That's put my mind at ease and I'm glad I posted it here and not on the 'other' site - I can just imagine the replies I'd have had there, things like "Yeah, sounds like your ECU / speedos knackered, you need a new one." and "Thats what happens with these newfangled fly-by-wire thingys, they're not real Alfas!"