On '87 & later cars with electric speedos with the sensor on the rear final drive housing, is there an electronic/mechanical adjustment to correct speedometer error? Changed tires & wheels and have about a 1.5mph under-read on the speedo and most likely an under-read on the odo.

Uhhhhh, no, not really. The rear differential mounted speed sensor sends recurring, regular pulses to the speedometer. The speedo uses a microprocessor to send the pulse to the speedo and odo and "change the oil service light on at 5000k or what ever miles"

Also, from this speedo-odo array, the speedometer repeats the signal to the Bosch or Rex-Regina engine control systems as it uses a vehicle speed sensor for a final engine air to fuel ratio trim at cruising speed and for use by the air bag SRS system.

The only way you can change it is replacing the ring gear with the magnet load to a different ratio.

If you are aware of the difference between actual automobile velocity that the speed indicating on your speedo, you can be mindful of actual vehicle velocity so you comply to posted speed limits.

You may also want to acquire the more accurate mobile GPS sensors to know actual vehicle velocity. Helpful, too, with figuring fuel mileage. You can find these used on your craigslist or eBay or Amazon as well as new GPS models.

Take heart, most auto speedometers and odometers in RWD Volvos are inaccurate. You'd have to use a speedometer repair service, and they may be able to make modifications to the speedo-odo circuit boards based on tire size, final output drive ratio, and more. I'm unsure, yet the microprocessors on the speedo-odo array may be changed, though using such a speedo repair service is very pricey.

Does that help?

Let me know when Saturday morning cartoons are worth a damn. At least we can see Dragon Ball Z Kai, though heavily edited and Justice League Unlimited on the CW Vortex Saturday morning cartoon programming block.

cheers,

Dud.
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Dud,

Thanks for the input. I'd hoped there might be an adjustment possible without the theatrics of going into the rear end assembly. There is a speedo shop in Denver about 110 miles North that maybe able to work on it if I take it out and ship or take it to them. I do use a Garmin Nuvi GPS which is how I discovered the under-read of 1.5mph. Previously, with the old tire size, and with a recent rear axle assembly change to a lower numerical ratio (down to a 3.73 from the stock 3.91) the speedo accuracy was unchanged and nearly dead on according to our GPS. Guess the wife and I will have to mentally adjust to and allow for the difference until I can contact the speedo shop to see if they are able to make any change in the speedo display accuracy.

Thanks again for your input!

Roger

1.5 mph off is relatively accurate! At what speed is this amount off?

What size tires do you have? Tires with 25.0 diameter make most accurate speedometer reading, for example 195/65-15.
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