Speedometer off, reads 10-15 faster than normal

[Lawman86]

Ok, so I’ve been through this before on here, but when I mentioned it I hadn’t thought of moving the dials to adjust for correct speed. Since I’ve corrected the speed vs against 2 different speed apps, I plugged my Autel in and my engine speed is off by 10-15 just like it used to be on the dash. I had taken it in to reprogram because of I was thinking original owner may have had larger tires but then realized the ECM is still showing 10-15 over while dash shows less. Since the stealership had supposedly reprogram/reflashed it. What if anything is there that I can do? Anyone ever ran across this? I mean the speedometer is telling the ECM I’m going a lot faster, so it’s hard to do some on board testing while out on the road with the speed being off. Anyone got any ideas?

[Supreme Pizza]

I  don't know anything about what your working on, but if your speedometer is off, I would suspect that the tires are the incorrect size, the speedometer gear / sensor is incorrect part or defective, or the stepper motor in the dash gauge might be having a problem. Might be computer coding as well.

 

You can always use your phone as a "Speed-O-Meter" if needed. Google maps has a speedometer on it, as well as many other free apps.

[Lawman86]

Just now, Supreme Pizza said:

I  don't know anything about what your working on, but if your speedometer is off, I would suspect that the tires are the incorrect size, the speedometer gear / sensor is incorrect part or defective, or the stepper motor in the dash gauge might be having a problem. Might be computer coding as well.

 

You can always use your phone as a "Speed-O-Meter" if needed. Google maps has a speedometer on it, as well as many other free apps.

Replaced the senators on trans originally thinking it was that. I work at a gauge rebuilding company and it wasn’t the stepper motors, it’s a 2011 GMC Sierra crew cab z71 4wd. The computer says one thing while the dash says another now. The tech said he had input the stock tire size for the truck which is the ones that are on it now, and got charged $50 for something that didn’t work. So I took it home, checked the motors, after knowing I changed the sensor for the trans, I got my gps unit I use for my drag racing car, and used it in town and on the Hwy, and now I’m only3 mph too slow. Not a big deal to me. 3 under is better than 3 over. Dash doesn’t seem to be effected by the change either, all works like it did before the ECM just shows a higher speed on the Autel. I’ve even input it on my Autel to try and program it but it didn’t work. I’d bought the Autel before I worked on this and was waiting for it and just got impatient so I took the cluster to the shop and tested the motors and it just seems that the ECM is commanding it to show faster than what it’s really going like someone else programmed it to bigger tires and somehow it’s locked onto that size now. Hell if I knew what size tires it had I might put them back on depending on how it looked.