So, I lent him my handheld code reader so he could check the codes. He told me he hooked it up, read the codes, cleared the cat code and then they car would not start. It tried to turn over, but did so just barely. He had to jump it to get it going. Then overnight it went dead again. So, he's thinking it was due to the code reader, but I'm thinking it's just coincidence and he has a bad battery, right? He drove the car around after that for a few days, without using the code reader, no problems starting.
So, he drives up here to NJ from NC and stops about 10 times along the way at rest stops, shutting the car off. Each time it starts with no problems. He gets to my house, shuts the car off and within a few mins, I hook up the code reader, read the codes, the cat code was set again, I cleared it. Then I go to start the car, and it barely tried to turn over just a bit. I was dumbfounded. Next I took a look at the battery. It looked old to me, he checked where he bought it and they say it's 3 years old. I pulled the caps off and found one cell that instead of water, had what looked like solid black crap in it. So, the battery is kaput. But the mystery remains. How could he drive around for a few days, no problems. How could he drive up here, stopping 10 times and the car starts, yet when you hook up a code reader and clear the codes, it can't start?
I thought about this awhile and the only angle I can figure is that resetting the computer causes it to somehow use more power on the next start? Like maybe it wakes up all the various electronic modules in the car to say hello, check status, etc, while it doesn't do that on a normal start? Any ideas? It's one of those mysteries that you since once in awhile.