Yesterday my battery died so I replaced it. This morning the engine was not very responsive and the check engine light came on after a couple of miles. I haven't checked the code, but I'm guessing it's the MAF. Would there be a correlation between the two or is this coincidence? I should mention there was very light rain while replacing the battery.

 

Post the code and then people can assist better. Best not to just guess...also...a bit more details about your ride...year, engine, model etc.

 

The battery won't have any effect on the preformance of the engine. It is probably a coincidence. Something else is wrong.

 

I would have to agree with snodbbs ^. The only time the battery is really used is when you are starting up your car then the alternator takes over from there anyway. My guess is that they are unrelated and there is something else going on...

 

Code is P0125 - insufficient coolant temperature for closed loop fuel control. Maybe I damaged the thermostat or ECT when changing the battery?

Vehicle is '98 4Runner 3.4L 180,000 miles.

 

Despite its name P0125 is frequently thrown by the O2 (or A/F) sensor being out of whack. It really means the ECU is confused by the sensor readings it is getting so that it stays in open loop, or startup mode, because it doesn't trust the readings it is getting. Don't waste time looking at the cooling system unless you really are running cold. How old is your O2 sensor? You should be about due for your third.

You did rule out an alternator problem causing the death of the battery, right? Because if you threw a new battery at a sick alternator you could be running a low voltage problem as the new batt discharges and a P0125 could be the first symptom. This would be the one case where what the folks above said does not apply. You should be seeing 13.5 volts or so at the battery with the engine running.

 

I'll check the battery voltage when I get home this evening. However, when I started driving this morning, first it felt better, but second, within 100 yards the CEL went off. Thoughts?

I'm not sure about the O2 sensor history. I bought this at 160,000 mi. Is an aftermarket replacement ok?

 

clean the MAF, reset the ecu by pulling battery again for 10 mins,

----
as the car ages, the ecu keeps track of how -out of whack it is- (sort of....)
and allows a certain tolerance for the maf and other stuff. sudden full resets of the ecu
(like a battery change) make the ecu want everything dialed again, and if there is a sensor
that has degraded (a dirty maf) suddenly it doesn't match what is expected

but yeah it is either a dirty maf, or o2 sensor or a/f sensor that may becoming ready
to fail