Mklll Golf GTi odometer issue

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Hi everyone, first time on this forum for my 1996 Golf so hope someone can help

I have a problem with the odometer, it's not giving me a mileage reading and is not increasing as I drive.

First noticed the issue a couple of days ago, the current mileage shows on the display until I start up the car and then I get either a flashing error message or 5 dashes (these alternate as I drive along), as soon as I turn the engine off the mileage re-appears on the display. The actual speedo works fine.

Not been doing any work on the car, battery v is fine etc..

Any ideas help please.

Cheers

Sarah