IMA Battery Problems after Dead 12v Battery Replacement
 

2006 Honda Civic Hybrid - ~153,000 miles, original IMA battery replaced under warranty in 2015.

My 12v battery was very old and needed replacing, but I foolishly did not replace it right away. Maybe a year ago, I had left an interior light on overnight and needed a jump. However, since then, if I left the car more than 4 or 5 days without driving, the 12v battery would die and I would need a jump again. It worked fine if I drove it frequently, which I was able to do until last month.

I had left it sitting for several days and found the 12v battery dead again and the car would not start, so I had it jumped. It seemed to work fine, but the battery died again after 3 days of non-use. I didn't get a chance to run the engine very long after the jump though, so I thought that might have been the issue. I jumped it again and it seem to run fine that day. However, the next day when I went to drive the car, it started with the starter-motor and the IMA, Battery, & Check Engine lights came on. I drove it a few blocks and the IMA assist wasn't functioning at all, so I pulled over and shut the car off. It wouldn't start again after that, wouldn't even try to turn over. And now it wouldn't even stay on when I tried to jump it. It would die again shortly after the jumper cables were disconnected.

My schedule didn't permit me to deal with it for another week, but I replaced the 12v battery. The car would now start (with the starter-motor), briefly, but then immediately die, and the green key immobilizer light was flashing, indicating that the car wasn't recognizing the microchip in my key.

So I had to get it towed to a dealer to have them re-program my keys, which allowed the car to start with the starter-motor and run just on the gasoline engine. However, the IMA assist was still not functioning. The dealer advised to bring it back for them to diagnose the problem. I needed to drive for work the next day, but I planned to bring it back the day after. On my way to the dealer, all the electrical systems went out and I had to pull over again. The 12v battery had drained again and I got another tow to the dealer. They are now saying that the IMA battery is not working and needs to be replaced. Unfortunately, this one is no longer under warranty so I'd be on the hook for the full price. I left a message for the dealer asking for the codes that came up, and I'm waiting to hear back.

I have two questions:
1. Could the IMA battery have been somehow damaged by the dead 12v battery or the repeated jumps?
2. Is there any possible alternative reason why the IMA would not work other than a damaged IMA battery? I checked the fuses and they were fine. I just want to explore all the alternatives and the guy at the dealer didn't sound like he was a hybrid expert, so I'm not sure how thorough he was in his diagnosis.

Thanks, I appreciate any advice!
Thanks.

Re: IMA Battery Problems after Dead 12v Battery Replacement
 

If the IMA battery is bad enough the car won't charge the 12V battery unless the RPM are in the proper range. There should be a warning light on the dash when this is happening. So even if you have a brand new 12V battery it will seem like it is bad unless you pay careful attention to make sure that it is charging.

If you decide to replace the IMA do not buy it from Honda! Get one from Bumblebee instead. The 2015 IMA replacement was almost certainly populated with old sticks scavenged from original packs, so it is now really 9 years old, not the 3 you think. That it has failed is therefore no surprise. Bumblebee will use all new sticks.

Re: IMA Battery Problems after Dead 12v Battery Replacement
 

Thanks for your reply.

So the dealer called up the chain with Honda for help and they were able to find that the IMA battery itself is ok, and that it was just the big fuse that goes with it that was blown. So they replaced that, but now they say a new code comes up for the DC-DC Converter. They are going to check with Honda again. Hopefully this is the last thing that's wrong with it.

Thanks.

Re: IMA Battery Problems after Dead 12v Battery Replacement
 

That makes sense. By running a failing 12V in it for so long, you were probably running the DC-DC at full capacity and eventually wore it out.

Should be nice and expensive and not covered under warranty. Suggest you shell out the $110 for a 151R or 51R battery next time.

Good luck,

Steve

Re: IMA Battery Problems after Dead 12v Battery Replacement
 

Hi Andrew,

I have the same issue in my Honda Civic 2007 Hybrid. May I know what you mean by the big fuse? Is it the big blue fuse in the secondary under hood fuse box?

Thanks,
Vajira