I bought an 06 H3 about a year ago and the speedometer consistently reads 20 mph low. What could be causing this?

 

20? What size tires mounted?

 

Lt285/70r

 

P.S. The chart doesn’t account for a 20mph difference. When my speedometer reads 10mph I’m actually doing 30mph. 30mph is actually 50mph

 

70r-WHAT:size wheel?

 

17” wheels

 

You have been driving it for about a year while this has been going on? How do you measure actual speed to make your comparison?

When was the last time you changed the Transfer Case Fluid? Do you have an MT or Auto Trans? Does your cruise control work?

The speed sensor (#6 below) is screwed into the Transfer Case above the fill hole to the right. The proper fill instructions for a 2006 require filling to the fill hole, then install fill hole plug (#10 below) and remove speed sensor to add an additional 250ML/8.45oz. Reinstall speed sensor. If the speed sensor is not installed properly, it either will not work at all, or may work incorrectly. I would not expect a constant error of a certain amount, but anything is possible.

There is another speed sensor inside the Trans that is correlated by the PCM with the T Case speed sensor comparing trans input to T Case output. That would likely cause different problems if bad.

Easy stuff first. Inspect the T Case speed sensor and wiring connector/harness. Check if it is loose or not installed straight. After all, it is an electronic part that can go bad as well.

Good luck.

 

I questioned this when I bought it and the previous owner said it was like that when they bought it. I think I’m the 3rd owner. I haven’t changed the transfer case fluid. I use my phone’s map app as a standard. Cruise control works as designed. It has an automatic trans.

I will check the sensor install and condition.

Thanks

 

if cruise holds at the correct speed then it might just be bad servo motors on the dash cluster.