No one-phase charge, DC-DC charge, P0A09

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Oct 23, 2023
Hello all,

before I get my hands dirty and approach the miev from under... I have a error code P0A09, I have no charge on the slow 1-phase factory charger and the main battery does not charge the 12V battery (the red light is lit when in ingnition). I've bought a new 12v battery, the car starts up and drives.

My suspicion is the DC main fuse that should solve all the problems here. Am I on a right track here?

And since the OBC isn't functioning I guess the fast charge is also out of the question, right?
The Chademo DCQC fast charging will still likely work okay even with this fault IF there is a good, strong, fully charged 12V auxiliary battery connected up front. The 12V will be loaded down during driving and charging since the DC/DC Converter is not working properly to keep the aux battery charged, so an external charger will be needed to keep the 12V fully charged.

There is a 20A HV fuse under the small cover plate of the drive inverter aka Motor Control Unit (MCU) located to the right of the OBC in the rear compartment. This fuse is in the path to charge the HV pack from the OBC, and also supply HV power to the DC/DC converter while driving in READY. Your car seems to fail both of these tasks so worth looking at the fuse. The cover has one Torx head screw to slow down your access, a useless PITA.

If the 20A fuse is blown, then time to look inside the OBC for possible snubber capacitor failure on the HV DC Output section or other damage on the AC Input section. Take a look at page 1 of the OBC Troubleshooting thread for pictures and links to posts. There is also a DCDC Converter thread but its not clear yet where your problem resides.

Where are you located and what year/model is your car?
Hmm... i did not seem to get any extra volts up front last time. It had only 10.8V left when I towed it home (a 3hr tow from a fully charged state). And I would not bet that the fast charger would work either. The 12V battery is just replaced brand new 35ah. I was betting all on the majn fuse regarding all the symptoms that occure.

The car is from 2012 and located in Estonia.
With a low, weak or old 12V aux battery, the car will likely NOT go to READY or charge by any means--either with single-phase AC or DC quick charge.

But with a good, fresh and strong 12V aux battery, the car may start to READY, and charge with HV DC on the Chademo port--but only for a limited time until the 12V battery is once again depleted because of the P0A09 fault (DC/DC Converter fails to charge the 12V aux battery). So don't try to drive except for testing purposes to find the root cause (diagnostic testing) or you will get stranded.

First check the fuse; if it is blown, then you must find the cause before replacing the fuse. If you just replace it then it will likely blow again.
Right now... the main fuse has no resistance... 0,03Ohms. To me its not the cause. Seems to work fine. I've remove the whole cover of the DC-DC converter, no burns, swells or explosions there.
The machine moves, 12V works, it doesn't charge @ 1phase charger and it doesn't charge DC->DC (330V->12V).

My money goes to the DC-DC charger (the left box). Luckily I have a donor from whom to fetch it. Gonna drain the coolant and see if that's gonna make any difference.
Did you check the fuses inside the OBC and inside the DC/DC Converter?

Have you seen the information on page 1 of the OBC thread?

also page 1 of the DCDC thread?
coulomb said:
riburada said:
I've remove the whole cover of the DC-DC converter, no burns, swells or explosions there.
Have you checked both upper and lower cavities? The HV charrger is above, the 12V charrger is below.

Yeah I checked both "floors". There's nothing bent, burnt, swollen. No markings of heat. Also there are signs that it has been opened before, I can see any sealant in between, the fuses seem okay, I will test them all later on.
Dc converter replaced, fault codes dissapeared from the dash. I cleared them from the MCU and they didn't reappear after the replacement. 12V charge is now OK and the car recognizes that there's a charger cable attached.

Bad thing though is, I still cant get a charge from the socket. Replaced the charger, nothing.
Does it have like... some contactors on the way from 220V charge socket to the OBC? The 220V charger clicks three times as if trying to send the juice but the car does not have the ability to take the juice.
It might work in some cases, but in general clearing DTC codes doesn't fix the problem--they are helpful to identify the problem area and to guide the troubleshooting and diagnostic efforts. Once the culprit is found and repaired, then the codes can be cleared to let the car operate or charge normally again.
The code dissapeared from the dashboard, once the charger was replaced. I erased it later on myself and didn't reappear. But all-and-all it doesn't make any difference whatsoever if the car is isn't physically charging.
Maybe it wouldn't make a difference except that your original problem was lack of 12V charging from the DCDC Converter, you changed something and now that function is working.

But now you have another problem in that the HV pack will not charge using level 1 or 2 EVSE unit; there will be different DTCs for this issue.

OBC failures tend to be in either the AC Input section of the power board, or in the DC HV Output section. Troubleshooting and repair of these are covered in painful detail in another thread with index, pictures and links.
Decided to forfeit the search of the cause. Swapped the battery pack (soh 84%) from that one to one of my other one that had a pretty worn 55%.
Naah... Still no. I'm not worried though. All I ever wanted was a nice battery pack. Better if it was still running on its own wheels. Since it didn't, I just used the battery pack instead and gave the old donor even a worse pack.