I purchased my 06 HCH May 2015. Reviewed carfax and received receipt of purchase and install of new IMA battery. Haven't had an issue until recently. Before whenever i started my car, i would put the key in the ignition and turn it over, the car would do a silent start. (no cranking or engine revving) I thought his was a cool feature, no loud noises when i start my car early in the mornings. Recently when i put my key in the ignition and turn it over the engine wont start. All the lights flash on and power goes to the dash but engine wont start. I'd have to keep the key turned until the i would hear the engine start cranking loudly and finally start. Once on the road i had no problems with the IMA at all. Charging is good and auto stop functions normally. if i let the engine crank over and start then turn the car off and then turn the key again the engine will immediately silent start like normal. Lately it has gotten worse, when i turn the key my navigation screen flickers on and off, almost as if not enough power is reaching the dash and engine. Even though the battery seems to have an almost full charge when i turn it off for the night. I don't know if it's a battery issue or not since it all functions normally once i begin driving. No noises are heard when turning the key. It just won't silent start automatically like it used to. Any ideas?

 

I can't see your location, but in extreme cold, the BCM protects the IMA battery from potential damage and can trigger a 12V start instead of the using the IMA system. No batteries like cold, but NiMH can get damaged at low temps under heavy load. Your 12V starter battery is expendable and cheap by comparison.

I don't know the threshold, but it's likely around freezing.

Don't think that the big battery behind the back seat does anything for your instruments, lights, coils, etc. The car is heavily dependant on the 12V for all of the same things for which a normal car uses it. It can only charge it with the DC-DC converter fed by either the IMA motor or the IMA battery. Additionally, a weak or marginal 12V may trigger IMA codes.

Weak instrument cluster lights, navigation, etc. is either a wiring issue or your 12V battery.

Unless the 12V is new, I recommend you upgrade the 12V to a 51R instead of the stock 151R. You'll have to discard all the plastic battery housing pieces, but it's a comfortable fit. If it's new, you should confirm its health with an actual load test.

I also recommend something like one of these to monitor your 12V health:

http://www.amazon.com/s/ref=sr_nr_p_...nid=2470954011

Good luck,

STeve