Searching threads it looks like this commonly goes with p1074. Both banks lean. The only code is p1071 - left bank lean. First, and pardon my ignorance, this is a transverse engine so which is the left bank?

I have yet to start digging into this and it is my bro-in-law's truck and has 70k. I believe that he said that it did go on recently after an oil change - but that should have nothing to do with this. I also cannot say that he is the best at maintaining his vehicles. I will check for vac leaks, but any experience with this - on only one side, is appreciated.

 

The "front" of the engine is always the side opposite the PTO, the side that connects to the transaxle. So in this case the "left" side of the engine is near the bumper, the "right" near the firewall.

Check your codes again. You said you have a P0171 code, which is actually the right bank not the left.

As for why the code on only one bank, well that could be many reasons. That bank may have reached its threshold limit before the other, and they may both be running lean. You could have a low-flowing injector on that bank. You could have a bad HEGO sensor. There could be a vacuum leak on that side of the intake.

In other words, you could just do some of the "normal" stuff for this engine and replace the intake gaskets, which costs very little, or you could maybe have the injectors cleaned and see if that makes a difference. Since it has a few miles on it, you could also replace the HEGO sensors just as a matter of maintenance, but these are just guesses unless you have the equipment to monitor live data and see what the computer sees from its sensors. You might be better off just paying someone to diagnose it and then perform the repairs yourself.