help!........ and greetings!

Greetings everyone, long time lurker here but I think it is time I finally commit.

There is a long back story and lots of work done on my car and yes, I have searched the forums here but to no resolve.

Within the last few days I have been having the "There is a problem with the transmission P lock mechanism" popping up. It has been bad enough that my car can not be used at all.

I have checked the battery, it was a little low ( I believe this was due to some engine issues I was having) But it is charged and sitting at 12.4 to 12.3 when I am messing with it and if I can get the car to start then it does come back up to 13.9 to 14.0 volts. This is read off the display screen in test mode and directly from the battery with a multimeter. I have checked the trunk hatch, solid. The doors are all tightly closed. The battery terminals and connections are tight, clean and secure.

I am really at a loss here. It seems everyone puts this solely on the 12v battery but as mentioned it seems to be fine. Please help

 

I bought the battery 3 years ago, it is an Optima yellow top battery. And as mentioned it is holding a charge.

 

Again as mentioned, It was a little low due to not being driven and some engine issues I was having. But I recharged it last night, went out first thing right off the charger with 13.1 volts and it would not start. Now I may be mistaken but it seems if it were a battery issue that it would have started when at such a good reading. Immediately after putting a load on it it did come back down to 12.3 to 12.4 which is where it should be. Then I removed the 7.5 amp main fuse and waited 30 seconds and replaced it and it then started. But then shut it off and we went right back to where we were.

 

This is a good point and I had not been taking this into consideration. I will be right back with some results

 

So here is a quick run at a 45 second test x2.

Started at 12.8 volts, turned on headlights and it dropped to 12.37 momentarily but then slowly came back up to 12.41 over the course of about 45 seconds. Did it again with the high beams and the results are similar.

I am happy to replace the battery if that is what it needs but this does seem to be a good battery. The last time I had it professionally tested was right after I did my engine swap (about 2 months ago) and all the readings came back desirable. I did not get specs from the tech just that there was nothing wrong with the battery. Reason for testing is after the engine swap it had ran it down because the DC/DC converter was not all the way plugged in......DOH

 

When in ready mode it reads a solid 13.9 to 14.0 volts

 

As mentioned.......right off the charger the battery was sitting at 13+V. And 13.9 to 14 when running does mean something. It means that the DC/DC converter is doing its job. Being this is a process of elimination I thought it worthy of mentioning.

 

Again I am happy to replace the 12v, I admit I do not know enough about them to say one way or the other for what I do know about batteries, dry cell are an even bigger mystery to me. I am not a tech, just a guy with a decent head on his shoulders....from time to time.

I am really curious though what the other causes could be. Can this be a transmission issue, or possibly a sensor? Again I did do an engine swap on it myself not that long ago and beings that the engine was "good to go" and "low miles" but unknown to me, I have of course been waiting for the other shoe to drop.

 

And the real question, even assuming the battery is bad, and needs replaced. If reading such decent numbers even if not for more than a couple hours, would the car still being doing this? Wouldn't it think everything was fine initially and then start acting up after the battery started to fail again?

 

Thanks, that is my next step. Luckily I have a back motor for parts if needed. Since I did the engine swap I found out just how hard some of these connectors click on and how easy it is to miss one. I missed the snapping of the DC/DC converter when putting it back together and was amazed at the array of issues that can come up from a 12v battery. I will update here when I have looked more into this

 

I only have a simple OBDII reader and there is nothing being thrown that I can see