Considering Reviving a Dead HCH II
 

About three years ago a friend bought a low mile '08 Civic Hybrid at the insistence of her dad to save money. She paid way too much for it, but it got decent mileage.

A little more than a year later, she noticed the fuel economy was dropping, then one day the dash lit up like a Christmas tree and the car died. They took it home and her dad and uncle tried to get it going again, but couldn't, deciding that the IMA battery pack was dead. Neither are mechanics nor know much about hybrids specifically. It now has just over 100k miles.

The car has been parked ever since, as they couldn't afford a new battery pack. She's been borrowing a friend's car since the Civic died.

I'm considering helping her get it running so she can recoup some of her losses.

What is the likely problem? With the batteries being a notorious issue, I suspect that is the likely cause, but surprised that it would suddenly die like that. Any tips for diagnosing?
I'm an experienced amateur mechanic, but have never torn into a hybrid or EV. Am I getting in over my head?
Is it better to just dump the car for whatever she can get as is and not throw good money after bad?

I'd start by checking the 12v battery. That's usually the culprit, especially on a car that is only 10 years old.

Bad IMA battery leading to death of 12V battery. Sounds run-of-the-mill to me.

I've owned 2X '06 and 15 battery packs.

Classic HCH2 hybrid battery failure. Battery deteriorates to the point that the car is continuously recalibrating and force-charging, robbing the car of power and dropping the MPGs.

HV battery can fail to the point that the 12V won't charge anymore (no alternator; DC-DC converter from the HV system).

Per red, replace the 12V and start there. Also, check the main (-) cable and the ground straps from the engine and cvt to the engine mounts.

Once the 12V is replaced, and the ground are good, I recommend the following:

1) start and idle the car until the IMA system stops charging at idle (or 5 minutes).
2) disconnect 12V battery for 60 seconds.
3) reconnect 12V and repeat #1 for a total of at least 3 times - you want the last time to very quickly show full charged within a minute or two.

Grid charging may also be an option.

If I do this and it shows full charge, what does that mean? That the battery pack is fine? Or it's only MOSTLY dead?

If I replace the 12V battery and I can get it started, is it fine to drive to my garage (15 miles away) even if the battery pack is FUBAR?

It means you've given the car plenty of opportunity to charge without subjecting it to high current and are minimizing the risk of killing cells at low SoC.

If the car runs normally otherwise, then it's probably okay to drive 15 miles. The biggest risk is if the 12V charging system is inop.

NOTE that when starting with the backup starter, it can take several seconds with the key in the start position before it engages.

Can't the hybrid system be disabled and the car driven normally?

The G1 Insight and HCH1 can be bypassed by turning the master off and unplugging certain connector(s) from the BCM/MCM; however, the HCH2 is a different beast. On both of my '06, I could bypass it simply by flipping the master switch off. I would get 12V charging between 1500 and 3500 rpm or so. I maintained confidence in the 12V state by running a voltmeter in the cigarette lighter port.

Others have reported this DOESN'T work for them on other years, and their 12V is run flat. I know of no other way to bypass it on an HCH2.

The concern with bypass is retaining 12V charging. It's worth experimenting. One could also mount an alternator. I think somebody did it on this forum or over at Greenhybrid. It wasn't pretty, but it worked.