[cowboyt]

I've seen that kind of thing before. At your next fill-up, do it with a calculator and compare it to what the car's computer is telling you. Odds are, the car's computer is off for some reason.

How long has it been doing this, and was there any maintenance done on the car that might correlate with when this started?

 

[cerritos]

That's interesting. I'd never suspected that the car's computer could be wrong. I'll start to monitor the odometer readings and the amount of gas I added. Since I don't drive much on the S430, it will take a while to have a meaningful data.

The instrument cluster was replaced in March. The transmission was serviced at the same time. I wonder whether it's possible that some cluster parameter is set wrong that caused this.

 

[cowboyt]

Transmission service...that could do it. After I replaced the conductor plate on the 2003 S430, the car's computer reported incorrect MPG information for several months, in this case, about 20% too optimistic. Yep, even after resetting the "learning" in the transmission with SDS. But eventually it did go back to normal, and it was within 0.5 MPG almost every time from that point forward.

 

[cerritos]

How long has it been doing this

I only drove it for 200 miles since March, and don't know how long it has been doing this.

 

[cerritos]

My transmission service did not involve conductor plate replacement.

 

[tusabes]

I only drove it for 200 miles since March, and don't know how long it has been doing this.

There’s your problem none of these mileage computers are accurate on rarely driven cars

 

[cerritos]

That makes sense.