Speedometer inaccurate (not just the usual complaint!)

If it's constantly off you could probably tear the unit apart and physically move the needle position... Never done it though so I'm just speculating.

 

ScanGaugeII = 60 MPH
Garmin 885T = 60 MPH
Tacoma Speedo = 62 MPH
Mile Markers = 120 Sec / 2 Miles

 

I set my cruise control on 35 (because that was the speed) when I saw one of those police radar gun things that tell you your speed. I believe I was going 33 when I had it set on 35. Same thing with my GPS when I set it up.

 

Because your speedo NEEDLE is off- but the speedo signal is just fine. That is why the SGII speed read out (from the trucks ECU) is dead on with the GPS. The error comes from the digital (ecu signal) to analog (needle) conversion. The odo is still getting the digital signal and is therefore a-okay.

I'm not sure...I don't have a scangauge so I don't know much about them.

 

I've had the same issue in 4 rental cars with not matching GPS speed. They are: Chevy Colbolt, Pontiac G5, Dodge Caliber, and Toyota Corolla. I thought it was due to how my GPS doesnt have altitude in it's programing; GPS calculating speed thinking I'm at sea level while I'm actually driving a lot higher so covering more distance than GPS is thinking. For example, if I drove 60 miles in 1 hour, at sealevel I only drove approx 58 miles... Just a guess though, I could be wrong.

P.S. I don't know how scanguage works so I can't answer that one.

 

GPS uses timing signals- They are all relative to each other. So I don't think that altitude will create a speed discrepancy...but I'm not positive.