Speedometer vs. OBDII

I was playing around with my OBDII reader and I noticed that the OBDII vehicle speed was consistently 2 mph lower than what was displayed on the speedo in the cluster.

Is this a defect with my speedo or is this something Jeep did to keep us from speeding?

I've done the cluster-check where you hold the odometer button while turning the key and the speedo doesn't land on all the check-points like you'd think it should.

yea my 97 is that way too; i seem to recall somebody saying that all manufactures did that for a long time but stop as GPS's were becoming popular

I wouldn't worry about it. Most speedometers read a tad bit fast. Federal standards on cars for the U.S. market used to allow up to a 5% error, that was back in the late 90's. probally holds true today. Its always better to read a few mph fast than it is to have it read slower than your true speed. I'd imagine its probally down to like 1% or 2% error on most new cars unless you have different size tires or regear your differentials.

My 92 actually reads dead on with my gps after I went from 225/75/R15 to 30X9.5X15 tires. The only vehicles I have ever seen that were dead on accurate were certified speedometers for police cars. When I worked at vw we had a few cars come thru with the instrument cluster coded for european options and tire size and those cars all read way to slow.

My stock 2000 reads about 2mph faster than the GPS. Most cars are 1-2mph faster than actual IMHO.

I've heard that the worst offender in this game is BMW with a 10% error in speed readings.