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My speedometer and odometer both stopped working today. I went the gas station, and reset my trip computer as I always do when I refill the tank. As I was driving home on the highway, I noticed my speedometer wasn't working. It was oscillating between 0 and 40 mph, just bouncing up and down. I came to a stop, and the speedometer worked up until about 40 mph, then oscillated again, and then fell to 0 and stopped working entirely. I also noticed that my trip computer and odometer had stopped working. I'm guessing this is a gear issue, but wanted to get everyone's thoughts. I hit a few significant bumps on my drive, but the odometer reset right before all this started has me thinking its a gear issue. Would that impact both the speedometer and the odometer? Any thoughts before I explore having the gear replaced? I'm in the Bay Area so I was thinking of having Palo Alto Speedometer take a look. Thanks all.
Last edited by A4Ultrasport; Feb 14, 2026 at 01:55 PM.
Hi A4,
The speedometer is electronic. My understanding is that there is a circuit board with capacitors that regulate current flow to the needle. When they dry out, the speedometer reacts to the hard pulses and jumps in cadence that match the speed sensor's output pulses. All of the above is from what I have read, 2nd-hand, so it will need a little investigation on your part. Also, if that is the case, the cost of the capacitors is under a buck each. When soldering them in use a lead-based 60/40 rosin-core solder. The lead-free solder has a higher melting point, which can damage the board, and it also has much lower ductility, making it prone to cracking from vibration. Use a 25- to 35-watt soldering iron, not a higher-power one, to avoid damaging the board.
Hope this helps,
Andy
Last edited by pp000830; Feb 14, 2026 at 02:25 PM.
I would pull the speedo out and make sure all the wires are connected, if I remember correctly there are several connectors on the back side.
The other thing you might look at is to make sure bits of the broken/melted old gear didn’t get jammed somewhere to cause it to stop working.
These are remote possibilities but worth looking into.
Btw, with all the odometer failures in some German cars it makes you wonder about the validity of the mileages.
Speed is derived from the left rear wheel sensor. As shown below, the signal is conditioned by the ABS control unit and Central Informer. The speedo uses that signal directly (speedo pin 4), then conditions it and distributes it to a number of other consumers- one of which is the On-Board Computer. Since your OBC is also acting up, I'd suspect the speed signal - it's common to both. Check your Cruise control, too. More info here that may be helpful in tracking down the problem.
Update: After letting the car sit for a week, the speedometer and odometer are working again. I drove the car several times today, and everything worked all day. Truly scratching my head now. Guess I'll keep an eye on it and see when it happens again.
Curious if this changes anybody's thoughts on what might be up?
Unless the car went thru some traumatic event just before this appeared, it's likely to come back - intermittents are like that. No sense throwing money at it until it comes back - hopefully long enough to troubleshoot.
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Speedometer / Odemeter
