Battery Cables or ECM

[Jatanna Willis]

Hey y'all.
I have an auto 05 Wrangler X 4.0 that I rolled last year in a wreck. Finally got the time and money to work on her and she runs like a dream, cosmetic damage only, I thought.. until the battery started dying when we tried to get her to the body shop. Replaced battery and alternator and gauge is still reading low voltage. So, here is what I am thinking. The first responders cut my battery cables,cut them super short actually, when I wrecked it (even though they did not need to... GRR (my husband and I are also emergency service workers)). We've tried to use the existing cables and replaced the terminal connectors. I am wondering if there is a short in the battery cables from being cut and it's not getting proper connection, or is my ECM is going bad. I also noticed that the transmission will not shift out of second gear when the battery is near dead. It threw a code, but the check engine light went off when we replaced the battery and has not came back on.. yet..

Ideas, suggestions, advise.. anything is welcomed.

 

[ac_]

First don't replace the ECM unless you know for sure that is the problem. I suggest basic troubleshooting first.

First you want to change the battery on trickle for like 24 hours. That should give you a good charge. Then load test it. (Turn everything on) It shouldn't go below 11 Volts if it does your battery is bad. Next lets say it is good. Start the car and check the battery on the terminals, it should be over 12.6 volts. If it is not, it is not charging. Check it on the terminal clamps then there terminals. If it is 12.6 on the clamps, but not on the terminals, then the connections on the battery is bad. Lets say you are under 12.6 on the battery clamps then go further up and check where the wire comes off of the back of the alternator. it should be over 12.6 If it is, then the problem is somewhere between that spot and the battery.

That should give you an idea of a few things to check before replacing the ECM.

If your alternator is pushing more than 15 volts you may need to change the ECM as I believe the ECM does do voltage regulation.

To check for a draw, disconnect the negative battery cable and put a test light from the negative terminal to the negative on the cable. The light should be off. (If you do this give it a few minutes for all of the delay voltages drop. ie dome light or anything else that holds voltage after the key is off) I usually give it a half hour before testing this way.

If you have a light, you have a draw drawing on the system.

 

[Chris]

There could be more problems than meets the eye, especially if you rolled it.

Hoever, it's very possible your PCM is bad, which sounds like the more likely explanation. Still, I would do what @ac_ suggested first, before jumping to conclusions.