While travelling the roads for many miles this holiday season I discovered a few potential problems with my speedometer, odometer, and/or trip computer. It kind of went like this..... at 5 AM Sunday in the middle of Indiana on I-65 I decided to compare my speedo with the trip computer.

So I set the cruise control on 80 and reset the trip computer. The trip computer reported 76 mph over flat terrain while the speedo indicated a dead-on 80 mph.

That didn't seem right so I compared my odometer with the mile markers over a ten mile stretch of road (flat and straight as things are S of Indy) and found I registered 10.5 miles on the odometer over that ten mile portion of road.

Both instances indicate a 5% error in the reporting but why would the trip computer deviate from the odometer. Don't they use the same sensor somehwere (tranny most likley) to determine tire rotational speed?

I still have Auto Trans and the original OE tires (Potenzas) mounted. IS this something I should worry about? Can it be corrected? I still have 8K in warranty left.

 

You might be on to something, I've found the MPG to be about 2-3
off. On highway trips computer says 28 -29 MPG while actually getting
26-27 on 92 octane. Hope this is not computer problem calculating our TOTAL
mileage that would suck.

 

Hmmm... like getting out of the warranty period 5% early? But I digress.

 

My trip computer reads high as well. Says 24.5mpg on the highway or so and I only get 20-21mpg. I only run super unleaded. How are you getting such good mileage?

 

Not sure of why your getting that low MPG on highway. I have 20k miles and stock intake (for now)changed the air filter at 15k, run about 32 psi in tires (stock RE92's). I get 19-21 city driving regularly.