Hi,
I have recently replaced complete ENGINE (including IMA Motor excluding CVT Transmission & Engine wiring) of my 8th Gen (HYBRID) Civic. From the very next day, I have started receiving error P0A7F.
Once I clear/reset error (via my 327 bluetooth scanner) then I don't see this IMA error even if I drive for hours but yes IMA error light appears if I switched off car for more than 1.5-2 hours.
Before Engine replacement there was absolutely no IMA error.
At night, right after parking in my garage, once I rest the error and then in morning I don't see any error even if I drive for hours. But it again appears if I park for long period.

NOTE: Before IMA light comes up (Most of the time), battery starts re-calibration for one time.
After receiving IMA light, Autostop, Battery Charging (Green Lights), Motor Assist (White Lights) still works,

I will really appreciate if anyone can help in diagnosing the issue.

 

First of all, the hybrid is not an 8th gen. The motor and transmission are unique to the hybrid, and they share very few components.

I'm assuming you have a 06-11 Civic Hybrid (HCH2).

P0A7F = failed hybrid battery. Given the circumstances leading to the engine replacement, I suspect it sat not running for an extended period of time. The #1 failure mode of the HCH2 is excessive self-discharge of 1 or more of the 132 individual cells in the hybrid battery. My diagnosis is also supported by your description of the post-engine-replacement behavior (recalibrations, worse when parked).

Given the circumstances, it sounds like you're at the threshold of failure. It's highly likely that grid charging the battery will improve its performance and eliminate the error. It will require follow-up charges, typically once every 30-90 days or whenever you get a recalibration. Depending on the condition of your battery, it could be nothing more than an overnight charge every so often with a full grid charge once per year.

There are no guarantees that this process will work for you, but the fact that you can get significant operation between recalibrations and IMA light indications are very positive signs it will work.

Also, ensure your 12V battery is 100% good. I recommend replacing the 151R with a 51R for the 40% higher capacity. You have to discard the plastic shrouds, but it fits pretty easily.

Good luck.

 

Thanks for a detailed answer. Yes, its 06-11 Civic Hybrid.

Please look at attached image for Battery Cells' Voltages status (after over night parking without starting the vehicle. Key position on switch-2).
I am assuming that battery cells are OKAY (are they not?)
Regarding 12v battery, after overnight parking its showing 11.75v. (without engine start). Don't you think that this is the ONLY culprit?

 

Are you measuring the 12V with a voltmeter at the battery with nothing on, or are you measuring it key on?

If you measured 11.75 via voltmeter at the battery with the car completely off, then you need a new 12V.

If you're measuring it with key on, then it's a little weak, but 11.75V UNDER LOAD isn't a concern.

REGARDLESS OF THE STATE OF YOUR 12v, What is concerning is the 15.70-16.50V range in your 11 IMA battery voltages. This is 100% confirmation that your hybrid battery has failed and is the cause for the P0A7F. Period. No question. No doubt.

In a healthy battery, its rare to see anything outside a 0.1V range, e.g., in your case, all 11 voltages should be 16.40-16.50V. A marginal battery has a 0.2-0.3V range, so it's possible that you have up to 5 of 11 semi-healthy sub-packs, but more likely, only 3 are good.

With a 0.8V range, it's no surprise at all that you're getting IMA lights on a regular basis.

The numbers you're seeing are confirmation of the typical HCH2 battery failure - pervasive self discharge of one or more cells in every subpack.

To summarize, your hybrid battery has failed with a P0A7F with 100% confirmation via the 11 subpack voltages. You MAY need a new 12V depending on how you measured the 11.75V, but any 12V issue you may have is NOT a factor in your IMA light/P0A7F/recalibration issues.

What else aren't you telling us? It's pretty shocking to go from your initial post to professional grade diagnostic data.