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Re: Checking speedo
From: Sachelle Babbar <firstname.lastname@example.org>
>How do I check if the speedo head is fried on my car? The trans hall
>sender is good. I don't know if it is the wiring, speedo head, or another
>component. By the way, it IS electronic.
All the sender does is ground out the input pin on the speedo - on my Avant
it does this 6644 times per mile. If you turn on the ignition, then you
could test out the speedo by tapping a grounded wire against terminal 31b
(pin 9 on the IC - UAF 1025 or equivalent). After 6644 taps, the odometer
will have incremented by one mile (or after 50 or 60 taps, the last digit
will have nudged forward about 1/10th of 1/10th of a mile.
I usually drive this pin with a signal from an oscillator (+12dBm, 600ohms,
315Hz) which makes the speedo read 170.68mph!
It's worth checking for loose connections or a blown fuse before starting
any of this.
Contact me if you need more info. I have a circuit diagram of the VDO
circuit and a data sheet on the chip.
1984 Audi 80 quattro
1989 Audi 100 Avant