I bought 9v battery memory saver. It plugs into always alive cigarette lighter. This is used so ecm memory isn't erased when battery is disconnected for battery replacement and other works. I was wondering if 9v battery (about 300 mAH) is left in the lighter plug and the engine is turned on, what happens?. Can that extra 9v and 300 mAH do damage to electric components in the truck? Change the way monitors work, example? I wouldn't leave it for more than 5-10 minutes.
The alternator has a voltage regulator. Can 9v battery back feed and cause some kind of damage?

 

Why would you want to leave that device in the circuit if the engine is running?

 

I think the fuse of the circuit and the battery will mitigate any issues before that.

 

Thank you for the replies. I have ecm problem where drive cycle takes me to good reading on my obd2 reader, then if ignition is turned off for few minutes ecm loses the memory. I asked about this in other threads. Not this forum but someone mentioned that truck will be ok but the battery could see trouble, possibly explode. I don't know how that would work but I'm believing the poster and will not try running the engine with the battery plugged.

 

Why would this battery hold the memory in the ECM if the truck battery won't? Have you tried this? Why not just fix the ECM battery? Or, replace it with a Reman ECM? It seems as if you are trying to put a band-aid on instead of fixing the problem in such a way as that it will not return any time soon.

Jonathan

 

i think the only way to roundabout solve your issue is ON power to your ECM despite key OFF but that is not really long term or logical

 

Sorry for the wrong impression. I will not use this to "fix" any power problem to ecm. Just to pass this year's inspection. But it looks like memory saver is not going to work. I've seen a video (a good mechanic) where 9v is plugged in first, then the battery removed, so assume those few minutes are ok, but that is without the engine, and the alternator, running. In nj and absolutely the car has to be engine off at the beginning. The inspector himself must start the engine. I asked. Then while the engine is off, ecm loses the memory. I was hoping 9v will keep the KAM. I also asked the inspector if he will unplug the memory saver, but absolutely not.

 

Stop creating new threads for the same question on the same truck.

 

I think of this question, and some others, as a separate issue apart of the main pcm problem I was having. That is because I'm thinking: what's memory saver got to do with the convoluted (in my mind) pcm problems? And so what if I go off track a bit? Anyway, your publications are very well appreciated.

The 9v memory saver did not work. It does have a diode so it didn't blow up the battery or anything even with the engine running, but it didn't keep the kam. It is possible that it didn't work because my original pcm was faulty. I say faulty only because now the truck works with new pcm. All of this was over my head. I think better way to handle some electricals would be to remove the fuse instead of the battery. Radio, for example. If replacing the battery, 12v (like the youtube mechanic) may be an option.