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Speedometer v. OBDII v. GPS

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I installed a Pioneer AVG-VDP1 Vehicle Dynamics Processor in my car a few months ago and it informed me that my speedometer was about 7% fast via GPS. Recently I bought an Innova 1303 for clearing CELs and checking codes, and I noticed the "Live Data" feature is able to read some engine info. What surprised me is that the MPH readout from the OBDII port is correct and matches the GPS reading. Why would the speedo (both digital and analog) read out different values than the OBDII computer? Is there some calibration step? Thanks!


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Please do a search here - this topic has been covered many many times.

You know, before I posted this, I was thinking about how I should probably do a thorough search before posting... yet I didn't. I'm not surprised that it has been covered. Sorry for my negligence and Thanks for the heads up!

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Don't feel bad at all, I had brought the same topic up a few weeks ago and DID do a search. While I love the people at Renntech, this has to be, hands, down , the absolute worst search engine of ANY message board I have been on (at least 20-30). It CONSTANTLY returns topics that have NOTHING to do with the keywords. Very frustrating.

To answer your question, the speedo is intentionally 4 to 5 mpg high for liability and european laws. My PGS also corresponds exactly with the Autoenginuity software reading the DME speed.

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