In my country, people believe that some vehicle sellers reset the mileage of vehicles to a lower number when selling the vehicles.

I want to know whether it is actually possible to do this in modern vehicles, and if it is possible, whether there is a way to identify that the mileage has been reset.

Also, is it possible to identify whether any engine trouble codes that were previously there has been reset? Does the ECU keep track of trouble code resets?

  • It once happened to a work colleague "by accident" when his company car went in for scheduled maintenance at a main dealership, and came back with 20,000 less miles on the clock than when it went in. Unsurprisingly, no explanation was ever given. We just assumed somebody had "clocked" the wrong car, either legally or illegally!
    – alephzero
    Oct 1 '19 at 16:06

Yes, many ways, one being replace the dash cluster.

For the codes, once they are cleared then they are gone... I have chatted with garages and one with dealer level readers and once cleared...

  • I can verify that. I replaced an instrument cluster when it malfunctioned at about 55000 miles, with one from a scrapped vehicle showing 75000 miles, and I inherited the larger reading (I didn't really mind: the vehicle was 14 years old at the time). This is one reason why you should always buy a vehicle with "full service history" showing the mileage at each service. Oct 1 '19 at 16:03
  • One thing you don't mention is, the mileage is stored in several places in the vehicle electronics (on most newer vehicles since 1996 and the advent of OBDII ... or there abouts ...). If the cluster is reset through electronic means, it is not uncommon for the cluster to reset itself to the actual mileage, though that may happen tomorrow or a year from now, no telling. With it being stored in several places, I would venture to assume there is a way of pulling the mileage and being able to tell if it was changed on the cluster (or if the cluster itself was changed). That's a guess on my part. Oct 1 '19 at 20:25

Yes it is possible. I commonly offer services for mileage correction on old and new model cars. There are some tools designed just for this and can be done via OBDII port other need to be calculated and modified manually in the eeprom memory containing the mileage data.

Most of us who do this type of work are honest and are correcting mileage to match actual mileage after the part has been replaced. In many cases we may be even rolling the miles UP but as always there are those who are not so honest and do things they should not. I see this quite often in some of the specialist forums I hang around in.

Sometimes you can use a good scan tool to check other modules like PCM for mileage and compare but not always. Unfortunately there is no one way to confirm but your best bet is to check for maintenance records and use good judgement.

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