Hey all, this one is hurting my head.
The car is a 2000XKR. Never spent the night outside, never modified, 49k miles. First the right passenger window seemed to lose it's ability to properly lower itself when door opening. Everything I have read indicated it was a battery low voltage problem. Didn't seem like a crisis, so after a couple month's (I'm a bit busy) I found the time to have the battery checked...the results were good.
Later that very day I right after battery testing, I got an orange indicator that later turned out to be p0171/p0174 (L/R banks too lean), and at one point a restricted performance alert. While I wasn't that in tune to the timing of it all because the top was down in Florida (really bright), it was as if they connected their battery tester and caused the car to go kaput. Once the restricted performance indicator went away on it's own, I got on it a bit in sport mode...the car runs great, but I still have the little orange indicator. I don't think the fuel pumps/pressure can be faulty given the rate of speed I attained...but did not check the fuel pressure.
Today a message appeared (wife was driving) stating the coolant level was low. OK, i haven't checked it yet but less than 2k miles ago (8 months ago) I replaced the fluid and thermostat. The cooling level I will check tonight. maybe it's a combination of a battery, vacuum leak, and bad coolant level...but I don't buy it.

So the question...what kind of dumb things might make all of this happen at the same time...could the battery voltage actually be low causing all of this and the kid that checked it missed it? What can low battery voltage cause? Any input is appreciated!

All the best
Twinsfather
(their 16 now seeking education at West Point...I could be screwed financially for life :-)

 

Was the battery load tested, or did he just take a simple voltage reading?

 

A load test will significantly drain even a good battery. If the rest of the charging system is not up to specs that would explain at least some of the symptoms you describe. Ask the parts store to check the electrical charge system.

Probably not the low coolant but these cars are famous for tiny coolant leaks. 'Rent' a pressure tester while you are having the charging system checked and test it cold.

 

You have three of the most common problems on these cars. Fortunately none are major if they are attended to.

Chances are your battery is on the way out, or the charge is low if you do not drive it regularly. That would explain the window issue. Another way to check it is to read the voltage across the battery after the car has been off for 8 hours with a digital multi-meter.
Under 12.3-12.4 volts is a bad or undercharged battery.

There is probably a slow coolant leak in the system. As test point states, a pressure tester is the best way to locate it.

There is probably a small air leak in the intake system, past the MAF sensor, causing the P0171/4 and the restricted performance. It could also be a MAF sensor problem.

 

I checked the radiator fluid last night. If low it's only by a few tablespoons. I'll add the 1/4 cup.

I did not mention it before, but I cleaned the MAF sensor after getting the P0171 and P0174 codes. Inspection of the duct revealed no cracks and the gasket at the throttle body was soft and plyable and fit well. Sure wish there was an easy way to find vacuum leaks....sure miss my 68 Firebird now!

 

One technique is to monitor the short term fuel trims with an OBDII reader, then spray either starting fluid or water around various intake seams...when the values start fluctuating wildly, you found your leak.