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Q: SUV slowed from 60 to 40 mph and lost acceleration

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While driving over 60 mph on a busy highway, my SUV suddenly slowed to 40 mph and It thought it was going to stop. I pressed the gas pedal, but it did nothing. Then I tried to move to the right to avoid having an accident and while doing this, the SUV independently shifted and started accelerating again. After that I got off the highway and took back roads to get home. The next day I took the vehicle to the dealership and they could not find anything wrong with it. The engine light had been on for over a month, but even with that, they couldn’t locate the problem. They told me to come back if it happened again. One night I went to the store and on my way back to the house, the SUV completely stopped in the middle of the street, fortunately near the house. A neighbor helped me push it into the driveway. The next day it started and I took it to a different mechanic to have it looked at and the new mechanic told me the same thing: he would have to experience the problem before knowing what to do. I feel totally unsafe in this SUV. I don’t understand why the diagnostic tests don’t show anything. Can you give me any advise as to how to find the problem for this?

A: Diagnostic codes can be somewhat transient....

Diagnostic codes can be somewhat transient. If the engine management system observes the problem clearing after several drive cycles, it will turn off the Check Engine Light and clear the problem code. There is no "history file" kept. There are devices available to the dealer which they can temporarily install which can capture the state of the system when the driver presses a button for instance, allowing capture of temporary problems such as this. You can also purchase a device which plugs into the diagnostic port of your vehicle (On-Board Diagnostic II), which comes with an app which runs on your smartphone. This allows you to access the diagnostic codes immediately when the Check Engine light comes on, so that you can have a better idea of the problem.

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