I have been reading through a number of the threads on here the past few days trying to figure out what is going on with my car. First the IMA light came on but went off the following day. About a week later the IMA Light came back on along with the Check Engine Light. I went and got the codes pulled and I had P1600 code and P1449. This morning when I started up my car and began to drive to work I noticed that the battery light was coming on when the car was around 1,000 RPM and would go off when it went a bit above this. Does anyone have any ideas about this? Is this most likely more than just having to get the IMA battery replaced? Is it alright to drive the car or would it most likely end up not starting at some point?

You might be interested in knowing there are 4 subcodes associated with a P1449. You can find out which one by reading the Blinking Light Codes. This is described on the Insight Forum under a post called Reading Blinking Light Codes.

I was getting the 12V battery light coming on under 1600 rpms when I had a blown 100 amp fuse on the 144V battery. However, I was also getting a P1575 code then. After fixing the 100 amp fuze I now get a P1600 and P1449 (subcode blinked out on the IMA light of "78" which is Battery Module Deteriorating...one of the subcode definitions) when using a code reader. My 12v is being charged ok or at least the 12V light is not coming on at the lower rpms. My CEL blinks out a "69" which I have been unable to locate a definition for. I would find out which subcode under P1449 is there and maybe that will give a clue as to why the 12V is not being charged at low rpms. Please post what you find out. You might also just get the 12V battery tested. Lots of strange things seem to happen wrt the IMA and codes when the 12V goes bad.

I have a 2004 HCH with 220K miles and this 12V battery thing is annoying the heck out of me. It is very annoying and unpredictable. The problem always initiates on ignition and is very sporadic. If you start the car and the battery light flashes then goes out and stays out (as it should) you are fine, but if it comes back on your driving experience is a nightmare. It's almost as if you have a bad altenator, but the car never shuts off completely it just operates vith very low voltage throughout the system. radio cuts out, transmission doesn't work properly (very jerky) and acceleration is annoyingly slow from a standstill (feels like you are stalling out). After about 1200 RPM the light goes out and it feels almost normal and on the highway (cruising) it's like normal. I can't seem to figure out what triggers it to get into this "low voltage" mode. I know when you disconnect and reconnect the battery it resets the system and your next start up is usually normal (with no 12V batt light on). Strange and weird stuff! I was gonna get another HCH, but too many issues when the battery goes bad!

You might have a bad/weak 12V battery coupled with a deteriorated/weak 144V battery. IMA light on? May be the car is shutting down the DC-DC converter (144V to 12V).

The Civic IMA/"alternator/generator" does not put out enough charge below 1500 rpms. During theses times(at idle) the 12V pulls charge from the 144V. If the 144V is weak and/or the DC-DC converter is shut down due to a certain 1449 code/subcode the 12V will not get enough charge to run the ICE properly if the 12V is weak/low charge.

Resetting the codes by disconnecting the 12V will allow the DC-DC converter to operate again until the car detects a bad condition and resets the IMA code(bad 144V) and shuts the DC-DC converter down again.

Got a brand new 12V battery, but the problem persists. On similar note, I was traveling on the hwy yesterday (10hr trip) and was pushing the car a bit. At around 7hrs of driving, the 12v battery light came on and stayed on while cruising on the hwy. This stayed on for about 30mins then the car just died at 80mph... I mean everything died...lights, engine everything... very scary moment. I immediately pulled over turned the ignition off and on and it was as if nothing happened! Just a warning for anyone who sees this happen... it's best to take some preemptive action and reset battery before this happens. Thank goodness it wasn't at night and traffic was light. I plan to install a breaker switch in the cab of the car to disconnect/reconnect the battery to reset the system.