Alright.

I am stuck.

I have been happily driving HCHII for the past 4 yrs. In 18 I bought a bumblebee IMA battery. That car ended up totaled (airbag) deployment. But ran fine to the scrap yard with no codes.
Fast forward. Got another 08 civic hybrid with a bad battery in it but still driving. My 12v light was on. Figured it was one of the IMA codes. Swapped my 2018 bumblee battery in it and the 12v is still on.
No IMA light.
No CEL
On a chance, I replaced my 12v battery with a new Duracell battery.
12v still on. No codes.
I have driven it 50 miles between. 12v trickle charges waiting for a light to come on with nothing.
I replaced the DC DC converter with the one out of my air bag deployed car.

Still on

I'm still charging my IMA battery and have good performance.

What are the odds the DC DC went bad in 2 months of sitting/when the airbag blew.

Any other tips?

 

Assuming you live in Michigan, corrosion is likely a problem After 11 years, it's probably a good idea to replace your main (-) battery cable and the grounding straps. They can corrode internally yet look perfect.

Do the CEL and IMA lights come on with key to ON prior to start?

When you say "no codes," you've checked it with something besides a cheap consumer OBDII code reader?

Based on what I've read so far, sounds like the DC-DC. I'd try another.

 

Thanka for the response.

Yes indicators come on when key is on.

Continuity from negative battery terminal to the body including when I twisted and moved the cable.

Continuity from grounding strap to the body, Measured with my meter it reads 0 ohms, too small for my meter to measure. I can get a more sensitive meter from work but cant believe less than 1 ohm to prevent charging all together.

Being from Michigan. Grounds are the first thing to get checked. 👍 I'm trying to prevent disconnecting the neg right now so I can see if a code will generate. Might be worth disconnecting just to replace the straps all together.

This will be the 3rd DC to dc converter. Seems improbable right?

Code reader it's not as sophisticated as I want but usually reads stored codes fine and history. Nothing for the past 50 miles.

Any recommendations for a good PC based scan tool?

I missed the passenger side. Will check when I get home. Maybe I will be pleasantly surprised.

 

Have you confirmed that you are indeed NOT getting charging?

If you've covered all the basics, the only reasons the 12V light is on are:

Cause related to a DTC - typically IMA related
DC-DC converter
Gauge control module

O'Reilly Auto parts uses Bosch brand code readers and read codes that your basic code readers can't.

While it would almost certainly cause a code, are you certain you installed both the IMA battery and the DC-DC correctly?

An IMA battery over-temp condition, which may not set a code, will cause 12V charging shutdown. The cable from the car to the IMA battery temp connector could be at issue.

 

It's a Bosch 1350. I got it in sale for near 70% off. Im looking to replace soon with more live time data.

Can you run me through the process to confirm I am not getting charging?

I have 12.9v new battery resting.

Start the car and monitor with my meter using alligator clips at the output taps from the DC DC converter. Voltage drops slowly but steadily while running down to 11.8v until I recharged the battery.

I still make mistakes but I'm not sure what I could do wrong while isntalling the pack/converter. Everything is tight, everything fits. No spare parts. Leads are correct, connectors are seated tight.

I've checked the pins in the the bcm, and ecu for corrosion/damage. I haven't found anything.

As for the cooling, it's been garage parked, 60*. The battery light comes on within 5 sec of the car being on. Almost like something shuts the converter off. I can hear the fan running when charging in park, and the light never goes off, even when i hit mid rpms.

I ordered another dcdc. Will try it.

 

If you're saying you hear the IMA cooling fan in 60°F weather, then the car thinks the IMA battery is hot. IIRC, the fan doesn't come on audibly until about 90°F.

You've likely identified the cause - the car thinks the battery is hot when it isn't, so 12V charging is disabled.

 

Thanks for your time.

Let me clarify: The car isnt parked in the sun but inside at about 60*, so the pack doesnt start hot. The fan is not on when the car starts or idles or drives normally. However, if I drive spirited, or accelerate hard (all assist bars) the fan will come on. If I sit and idle high to attempt a force charge (as some other posts suggest their 12v goes away with high rpms) the fan will come on after a min or so of higher rpm. Do you have a test where I can see if the car thinks the pack is overheating? Ill gladly follow this lead until the new Dcdc arrives.

 

Living here in Phoenix, I rarely heard the fan come on even with the pack was over 100°F. I can't imagine that your "spirited" driving would cause a 40°F temp increase.

To my knowledge the only way to tell the pack temperature is to hook it up to HDS to read the reported temps.

Regardless, if the fan isn't running at cold start, and the 12V isn't charging, then it's not likely a temperature issue.

Did you torque the main bolts when you attached the main leads to the batteries?

Do you have access to the entire IPU from the totaled car? If so, probably worth swapping over the MCM/BCM.

 

HDS?

It is not running at cold start, and still not charging.

I toqued them by hand, snug, then a hair more with my ratchet.

I wish I had access to the entire IPU, Im still kicking myself for selling it without the entire thing pulled.

If I guess at parts next, it will be the, BCM, MCM, then the ECM. However, I have seen these go bad in other HCHII ive had/worked on and have and all have thrown codes when they go.

 

HDS = Honda Diagnostic System

Agreed on codes.

The simple solution is the DC-DC. Let's hope that's it.