About 5 weeks ago, my voltage meter on my dash started going down. I automatically assumed alternator or battery. Took it to Autozone and had the battery tested. They said the battery was fine but there is either an issue with the alternator or ECM. To know for sure I would have to remove the alternator and bring it in from a bench test. Removed the alternator, took it in. Alternator is fine. So must be ECM. I bring the the alternator back home, put it back in my jeep. I start the jeep up just out of curiosity and bam the voltage meter is back where it should be right in the middle and everything is fine. Everything was fine for 5 weeks. Today, the voltage meter is back down around 9. I have checked my connections to the alternator, removed them, put them back on, still gauge reads close to 9. Unhooked the battery for a little bit, hooked it back up, still 9. So here is my question. Could the ECM still need to be replaced? Why would have it corrected itself after I took the the alternator off and then reinstalled a day later? Does pulling the power from it for a bit reset it or something? Before i buy a new ECM I want to explore all possibilities. Any suggestions?

 

If the engine still starts with the gauge reading 9 volts, I would suspect the primary battery wire from the battery to the PDC being corroded or loose. The PDC is the fuse/relay box under the hood. Look for corrosion around where the wire comes out of the battery cable clamp.