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Old 11-27-2015, 10:21 PM   #18 (permalink)
S Keith
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Originally Posted by rpearson View Post
I am rpearson's husband. Don't want to confuse.

I went to auto zone and told them I wanted to replace the battery although I didn't actually believe it was bad. They said take it out of the car and we'll stick it on our charger/tester and you'll know for sure. An hour later they called and said the 12 volt was fine.

In all this I also found a bad IMA fuse in the fuse bank under the hood. Replaced it. I haven't measured any voltages since replacing the burnt fuse.

I'm not really sure what is going on. The 12 volt seems to be charging as the car never fails to start. We've driven it maybe 200 miles without incident.

The only thing I am certain of is that we get the error code P1639 and that the IMA charge/assist lights don't come on.

I've reset the error codes several times and P1639 returns within 10 seconds or so. My wife and son think the car is actually receiving assist from the IMA system. I'm not sure about that. The charge/assist light comes on when the ignition is first energized but then goes off. I guess there is a moment where it says it is charging at 3 bars for a few seconds when the car is first started and then it goes off and stays off. Tomorrow I plan to put the old IMA battery back in and read the error codes with it. Then put the new IMA battery back in.

How do you replace the red IMA light? It seems that would be an additional diagnostic that would be good to have. What does the MOTD do?
If the 12V light is on, 12V charging inop. If it's off, the 12V is charging. Your wife confirmed is it on at idle but off at 2000rpm. This means the DC-Dc converter is working w/o the IMA battery. It's charging the 12V based on its input. Idle output of the IMA motor is too low, between about 1500 and 3500, it's good, 3500+ is too high.

Your wife linked to a thread on Greenhybrid where someone had the same code. It was a missing fuse.

The next diagnostic in that thread was to swap out the MCM (one of the boxes in the IMA cavity with the battery) with a used unit.

Unfortunately, I don't have a service manual for HCH1. The HCH1 is closer to the Insight than the HCH2. The Insight mentioned a P1638 code relating to the MCM, but the HCH2 has nothing close.

The diagnostic for the Insight is to reset the MCM via the #18 Back Up Fuse (under dash) or the Honda Diagnostic System. It does not indicate that a 12V reset would do it, but I'd be surprised if it didn't. If that doesn't correct it, replace MCM with a known working unit.

Probably a good idea to confirm you get the same codes with the old pack. If you don't, you can try to swap the junction boards between the packs. It's pretty easy. If you go that route, be careful, there's 90V or so exposed when the junction board's off. Do NOT touch more than one of the Aluminum spacers at once.

Don't know how to replace the IMA light. Likely have to access the back of the cluster.

You might consider a service manual of your own:

2003 2004 Honda Civic Hybrid Shop Service Repair Manual CD Engine Drivetrain | eBay

My HCH2 manual is from that source ("Bishko", not that seller), and I've been very happy with it.

Good luck,

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