You have been seriously misinformed. First of all, there can be well over a dozen relays, but there isn't one for the odometer. A relay is an electric switch that uses a small current to turn a high-current device on and off. A tiny ignition switch turns a large starter motor on and off through a relay. A puny little computer circuit turns the radiator fan motor on and off through a relay.
Going way back to the '90s, the instrument cluster is a computer module that talks back and forth to the many other computers on the car. Even on the late '80s cars I worked on at a Chrysler dealership, the odometer mileage was stored in the Engine Computer. We could easily change that if it was wrong, but it was only wrong if that computer had been replaced and the mileage wasn't updated. Changing the mileage in the Engine Computer doesn't affect what is shown by the odometer. It simply changes when the "Maintenance Required" light turns on the next time.
To change the mileage shown on the odometer, at a minimum you would have to replace the instrument cluster. On a lot of cars that involves programming it to the vehicle's ID number, and often that can only be done by the dealer. If an instrument cluster is sent in for repair, they read the mileage, then program that value into the cluster they send you.
Changing the mileage is so involved, and you can't be sure it wasn't recorded in numerous other computers, so it really doesn't pay. The government has created way too many ways already for dealers to get in trouble without even intentionally trying to do anything to hurt their customers. They don't need to add odometer tampering to the list. Dealers even have to worry about a lawsuit involving YOU tampering with the odometer on the car you traded in.
Also, no one person can change the odometer reading. Someone has to order a different instrument cluster, someone has to install it, and they'll be wondering why they were asked to replace it. A used cluster from a salvage yard is just as likely to have a higher mileage on it. Someone at the salvage yard is going to have paperwork showing where that cluster went. How is the seller going to explain how the car can have a lower mileage now than what was recorded on the previous owner's title? We don't even talk about this issue any more, and there's little reason for you to worry about it.
The only way to stop accruing more mileage is to disconnect one or multiple speed sensors. Since Chrysler developed the computer-controlled automatic transmission for the '89 model year, a failed, (or disconnected) speed sensor would keep the transmission in second gear, would set multiple diagnostic fault codes, and would turn on the Check Engine light. Would you want to drive around all day in second gear? Would you buy a car with the Check Engine light on? The speedometer wouldn't work either. Your time is better-spent worrying about how the previous owner babied or abused the car you're looking at.
Be aware too, that as a generalization, customers who assume a dealer is out to defraud them almost always find some reason to be angry, even though the vast majority of dealers are honest and want your repeat business. Every week we had at least one naturally-suspicious person come through the door, and they are the hardest to work with and find the best deal for. Luckily most of our customers were satisfied, repeat customers, and they provided the best word-of-mouth advertising. When we know you don't trust us, what incentive is there for us to prove otherwise? As in every other profession, there are always the few of us who will live down to your expectations.
Saturday, June 27th, 2015 AT 9:31 PM