2011 GMC Acadia runs rough at 55 mph

Today when driving to work my 2011 GMC Acadia started running very rough at 55 mph and the check engine light came on. It ran fine at any speed below that, but the check engine light stayed on (solid). Any help on figuring out what the issue is would be much appreciated. It has 121,000 miles on it.

Have the error codes read and post them here. Most auto parts stores will read them for free. Post the actual number… in the form P0123… don’t just tell us what the counter person say they mean.

Hint… The counter person is not a mechanic!


The last time I borrowed a code reader from a parts store, the counter guy asked me to take a picture of the screens rather that provide a printout. Make sure you take your phone.

Expecting a knowledgeable automotive diagnosis from the guys at an auto parts store is not very different from expecting an accurate medical diagnosis from a cashier at Walgreens or CVS.


The car is trying to tell you what is wrong by lighting the check engine lightas This means that one or more trouble codes have beet set.
Those codes will tell lou what systems are reading sensors that are out of spec. A mechanic has to do tests to diagnose exactly what the problem is.

Sometimes replacing the main component of a system fixes the problem. Some times it does not.

That is why following a diagnostic tree prevents replacing parts unnecessarily.

you have given us next to no information.