P0121 - Throttle/Pedal Position Sensor/Switch A Circuit Range/Performance Problem
P1110 - Atmospheric Pressure Sensor Low Input
P1120 - TPS Out Of Range Low
At first glance, none of these have anything to do with the speedometer. We've been running into a lot of weird symptoms though that seem to have nothing in common with their causes. A friend recently ran into a truck that had a very noisy transmission, and that cleared up after repairing a broken wire for the ambient air temperature sensor. That one really surprised us, but we've been seeing more and more things like that the last few years.
You didn't list the right engine size so I'm not sure which throttle system you have, but if it's the "throttle-by-wire" system which adds another unreliable computer to the car, I can see where these things can all be related. There's two things to consider. First, have the dealer erase the fault codes, then test the electronic throttle system. If that solves the problem, at least for now, they may be using the speedometer as a way of getting your attention so you have the throttle system repaired. In my opinion, electronic throttle systems are dangerous and I'll never own a car with one. That's what put Toyota in the news a few years ago.
The second thing the mechanic can do is use the scanner to view live data to see why the cruise control won't set, and its "reason for last cutout". I suspect the "reason" will be "vehicle speed too low" or "below minimum threshold", but that will just verify what we already know about the missing speed signal. From there, he can see if multiple computers aren't getting the speed signal, or if just one computer isn't reading the signal being sent to it.
Thursday, June 18th, 2015 AT 7:18 PM