History/background
I have a 2004 Civic Hybrid manual transmission. A few minutes into a recent drive I heard a strange noise, then after a few seconds it went away. (It turns out this was the sound of a piece of debris dislodging my serpentine belt.) After driving for another 20-25 minutes I exited the freeway and found that the car then started bucking and hesitating. I pulled over and then noticed steam from under the hood from a leaking radiator. I let it cool, added water, and then was able to drive it the last few miles to my home. It started easily and drove normally. At that point I diagnosed the problem. Without a serpentine belt, the water pump was not turning and the car overheated. The resulting pressure caused the seals of the radiator to fail. The radiator cap also broke ad failed i a way that it did not relieve the pressure live it should have. (I found the spring from the cap in the neck of the radiator.) Since then I have replaced the serpentine belt and the radiator. In the process, I disconnected the 12 volt battery and removed it to make space.

Problem
When I reconnected the 12v battery. I heard a continuous clicking coming from behind the rear seat (from the area of the BMC & DC-DC converter). This clicking occurs whether or not the key is in the ignition. At the same time, the instrument panel lights flicker in time with the clicking. If the key is inserted and turned to position I (On) there is no change. In positions II and III (Run and Start), the clicking stops and the regular instrument panel lights illuminate that you would see during these operations. However, there is no sound or activity from either the IMA motor (for starting) or the backup "standard" starter. Whenever the key is not in position II or III the clicking/flickering continues as before. The only way to make it stop is to disconnect the 12v battery.

Questions
1) Has anyone ever had and/or solved this problem?

2) If not, does anyone have any insight into what the problem might be?

Without knowing what happened or why, I'm worried that just replacing the charger/inverter/converter or the BMC might just result in the new units being fried like the old.

The 12v battery is fine and starts & runs another Civic without issue. There were no sparks or arcs when removing or replacing the battery. I have done this on various vehicles 100s of times. Likewise, there were no issues with the serpentine belt or radiator replacements. The clicking is NOT the common clicking from a starter solenoid in a no-start condition.

I have been fixing cars (mine + friends' & relatives') for ~40 years and this is a new one to me.

Any thoughts?

Your ideas and responses are greatly appreciated.

 

I don't know

 

New info:
The clicking is coming from a relay in the compartment housing the IMA battery, DC-DC converter, etc. In the lower left corner of the compartment there is a connector holding two relays. The sound is coming from the top relay.

I also have a 2005 HCH1 that has transmission problems but is otherwise functional. I have been able to use it as a test bed and to swap parts. Doing this I have found out what is NOT the problem: the relays, the battery control module, & the charger/inverter/converter. No matter what parts I swap, the problem stays with the bad car and the good car behaves normally.

Also, the car is currently displaying DTC code U0110. The code description mentions a possible faulty BCM (which I've already eliminated) or an open or short circuit in the harness or connections. This is about the last thing I wanted to hear since chasing down a wiring fault is among the hardest and most tedious things to do.

If anyone has any ideas on where to start or helpful tips for chasing these thigs down, I'm all ears.