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  1. #1
    Junior Member
    Join Date
    Apr 2009

    how low should state of charge go?

    I recently purchased a new 09 HCH and I think something is wrong with the IMA system, but am not sure if the issues I have are just how it is supposed to work.

    The first issue is that the car will almost never assist if the SOC is at 4 bars or less. Sometimes it will assist until the bars are down to 3 bars, but then it won't assist at all, no matter the speed, elevation, how hard I press on the accelerator pedal or the engine RPM. I go through a lot of mountains so this is a frequent issue. I will start ascending an incline with a full or near full SOC, and the IMA will assist for about 60-90 seconds but once it reaches 3 or 4 bars, it will stop assisting at all. I end up driving up the rest of the mountain with no assist at all, at about 4000 - 5000 rpm, 45-50 mph (which kills my fuel economy). Often, the IMA is also trying to recharge the battery at this point. Once I reach the top, I go down the other side of the mountain, the battery fully charges in about a minute of coasting/regen (keeping the iFCD at 100 mpg), and then I have to apply the real brakes to keep the car under 75 mph (the speed limit is 65). I repeat this whole procedure through several other hills/mountains. Generally I know the rule of thumb is avoid using assist to maximize fuel economy, but in this case, whether the SOC gets down to 3 bars or 0 bars (if that is even possible), the battery will be completely recharged when I go down the other side of the hill, just by coasting, so I am wasting gas powering up all these hills without IMA assist, just to brake going down hill. So my big question is, is it normal for the SOC to only get down to 3or 4 bars before it absolutely refuses to assist?

    The next, related issue is that sometimes it does the same thing as above, but instead of no longer assisting at 3 or 4 bars, it will stop assisting at 6 bars! Generally this is just an issue of fuel economy, but sometimes it becomes a safety issue. The other day I was on a two-lane mountain road behind a truck going about 35. When we came to a passing lane, I went to pass but had a hard time doing so because the IMA wouldn't assist. The SOC was at 6 bars and I had to run the engine up to about 5500 rpm to get my speed up to 55 mph so I could safely pass before the passing lane ended.

    Possibly related, sometimes the SOC will drop from 6-4 bars rapidly. I read on another post that this may be normal if the car gets confused about the actual state of charge, but since I am having the other issues, I didn't know if it might indicate one or more of the battery cells is bad or something.

    No trouble lights have come on, including the IMA light. I took it into the dealer and they didn't find a problem with it, other than that there was a computer software update, but they also had a hard time reproducing the issue because there are no hills or inclines near the dealership. They also said that Honda changed the IMA programming to prevent the battery from getting low because people complained that the battery level would get too low and that it created a safety hazard. I would understand that if it saved the battery power for emergencies, like when you floor it, but my car IMA still won't assist when I floor it.

    Any insight would be extremely helpful.


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  3. #2
    Junior Member
    Join Date
    Oct 2006

    HI Tim; Much of what you

    HI Tim;

    Much of what you mentioned is quite normal.

    I believe you'll find the answers to many ofl your questions by reading the HCH-II FAQ. Just type the words "Honda Civic Hybrid Frequently asked questions" in Google and the top most article will give you all the explanations you need.

    Your dealer is also not correct regarding changes made by Honda to the Electric Assist affinity. With this said, this car was definitely not engineered for sustained sporty behavior and if you need to "floor it" on a regular basis you should at least attempt to manage its SoC.



  4. #3

    For passing situations

    For passing situations putting the transmission in S will help.

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