Tracking down ground fault error

Hi all -

My 2011 (battery replaced by dealer in 2016) is getting this error code:

P0AA6 00C0 EV/HEV Hybrid Batt Volt Sys Isolation EVC-157

After reading up, seems to point to a ground fault, ugh!

One clue: The 12V battery is putting out 7.5 amps with the car on, but all accessories off. That high current draw seems consistent with a ground fault, yes? I installed a brand new 12V battery a few days ago after the problem started. It's now at 12.1 V with the car off, dropping to 11.7V with it on.

Does anyone have DIY documentation they could share on tracking down ground faults?

Any thoughts or suggestions appreciated, thank you!

I think that the current leakage is from or through the high voltage pack, according to the error codes. The 12 volt system drain may well be related, but it may also be something else.

danbertolet said:

One clue: The 12V battery is putting out 7.5 amps with the car on, but all accessories off.

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That's a separate issue. How are you measuring this current? If with a clamp meter, are you zeroing the meter before measurement?

What does the drain fall to with the car off, and doors closed for at least 10 minutes? I assume that there is no EVSE plugged into the J1772 port.

That high current draw seems consistent with a ground fault, yes?

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No. The ground fault is leakage inside the high voltage battery, nothing to do with the 12V auxiliary battery. When the car is on (not ready), the main contractors are off, so the whole high voltage battery is disconnected from everything else. So the ground fault can't affect auxiliary battery drain.

I installed a brand new 12V battery a few days ago after the problem started. It's now at 12.1 V with the car off, dropping to 11.7V with it on.

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I'm guessing that you can't get the car into ready mode, which means you can't charge the auxiliary battery with the DC-DC converter. You should charge the auxiliary battery with an external battery charger. Try not to let it ever drop below 12.3V or so.

Does anyone have DIY documentation they could share on tracking down ground faults?

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Finding a ground fault isn't an easy DIY thing. You would have to drop the high voltage battery, open it, and using a multimeter with the negative lead on the metal of the battery case, probe various cell connecting straps or bars to find the place with minimal voltage reading. That will indicate the approximate location of the leakage. Obviously, this is a dangerous procedure, and requires the appropriate safety protocols, and should not be attempted unless you have high voltage DC experience or at least knowledge of the dangers.

Current you observe may well be low v battery charging current.

The error indicates that the fault is in the high v system.
As i posted earlier ALLDATA.com has the info on the error cause and testing procedure for high v leakage.
Generally a megger is used to test the insulation of suspect circuits.

Take a look at the Nissan procedure outlined in ALLDATA and see if it is something you can safely do.
After some procedures to isolate the problem it starts with disconnecting the high v and PTC heater harness( using appropriate electrical gloves) from the battery and discharging any remaining v on circuits to be tested.

Thanks coulomb, that makes sense about the auxillary battery being a separate issue.

I got the 12V current reading through LEAFSpy, so I can't measure it with the car off. No EVSE plugged in. So are you saying 7 amps is normal in on mode but not in ready mode?

I just reset the DTCs with LEAFSpy. Now the car goes into ready mode normally, goes into drive, and the 12V warning light has gone off. So I think my 12V battery is teetering on the edge (it got warmer outside since this morning).

Yeah, I hear you about the tricky business of finding a ground fault in the battery pack. I'm not going to try it. But I'm just trying to eliminate all other possible fixes before taking it into a shop.

cje, thanks for the tips. I'm a newbie and still have some learning to do before I can justify spending $$ on the AllData info.

Regarding the 12V battery current that LEAFSpy reads, screenshot at this link:

http://citytank.org/images/IMG_5823.png

I was wondering if the "-" in front of the 7.23V actually meant negative, as in, current charging the battery. Does the system actually work like that? (As I mentioned, newbie here...)

Update:

After resetting the DTCs, which allowed the car to go into ready mode as normal, I turned the car off and I tried my 120VAC trickle charger again. The first blue charging light on the dash came on as usual. While charging, LEAFSpy showed a DTC I hadn't seen before: P31C2 00C1 EV/HEV TCU EVC-273. Screenshot here:

http://citytank.org/images/IMG_E5827.jpg

The charging only went on for a minute or two before it shut itself down. I disconnected the charger, turned the car back on, and LEAFSpy now showed the same EVC-157 code as before, plus it kept the new EVC-273 code, screenshot here:

http://citytank.org/images/IMG_E5828.jpg

Just throwing this info out there in case it may mean something to someone, thanks for humoring me!

danbertolet said:

So are you saying 7 amps is normal in on mode but not in ready mode?

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No, that seems very high to me.

I was wondering if the "-" in front of the 7.23V actually meant negative, as in, current charging the battery.

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Certainly, the dash character signifies negative current, but there isn't a totally universal agreement on whether negative means discharge (feels right to me) or charge. [ Edit: Before you cleared the trouble codes, you probably could not get the car into ready, so you would not be charging, so most likely the negative sign indicates discharge. ]

I just reset the DTCs with LEAFSpy. Now the car goes into ready mode normally, goes into drive, and the 12V warning light has gone off.

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Right. When in ready mode, certainly just after the start of ready mode, your battery will be charging (assuming that the DC-DC converter is OK, and there is no reason to suspect it's not) So that will tell you the polarity convention. My Leafspy dongle has gone missing, so I can't quickly check, and I just don't remember for sure which way it goes.

So I think my 12V battery is teetering on the edge (it got warmer outside since this morning).

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Yes. Since yours is a 2011 model, with the same poor auxiliary battery charging as mine, you should get a voltmeter that plugs into the 12V round connector (used to be called a cigarette lighter outlet; what do we call them now?). Use the wipers to keep the battery at over 14V for as long as you can.

Yeah, I hear you about the tricky business of finding a ground fault in the battery pack. I'm not going to try it. But I'm just trying to eliminate all other possible fixes before taking it into a shop.

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An excellent idea. It's still possible that there is nothing wrong with the high voltage pack (no ground fault/leakage), and the fault codes are all a result of the 12V battery being horribly low on charge. It needs a good few hours above 14V to recover. Low auxiliary battery voltage is the cause of way too many false alarms in EVs. Just driving a 2011-2012 model Leaf to the shopping centre and back isn't going to recharge the auxiliary battery at all, sadly.

Thanks again coulomb!

You make it sound like spending $50 on battery charger would be worth the investment if I'm going to keep this car around for a while.

Luckily, I've got time -- it's a second car. Since I only paid $3500 for the car I'm loathe to start shoveling money into it at dealer repair shop rates unless I really have no other choice.

The "cigarette lighter socket" is now called a "power port." Dan, what we are saying is that the high current movement between the 12 volt battery and the car is likely because the 12 volt battery is very low, and the car is trying to charge it. It can only do so when it's in "Ready" (to drive) mode.

danbertolet- the DIY version of ALLDATA $20.00 very useful to learn operation and reference error codes.
Newbie myself so also trying to get a handle on what can be done without paying for diagnosis that may or may not be accurate.
Appreciate any updates that you can share.

Would it work to rule out the 12V battery if I cleared all faults, set up a jump, and while it has 14V from the other car, try the 120V trickle charger to see if it still shuts down and triggers the same fault code?

For reference:
P0AA6 00C0 EV/HEV Hybrid Batt Volt Sys Isolation EVC-157

danbertolet said:

Would it work to rule out the 12V battery if I cleared all faults, set up a jump, and while it has 14V from the other car, try the 120V trickle charger to see if it still shuts down and triggers the same fault code?

For reference:
P0AA6 00C0 EV/HEV Hybrid Batt Volt Sys Isolation EVC-157

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It would absolutely rule out 12V supply problems, but it's unlikely to help. That fault means the vehicle has detected a voltage leak between the high-voltage battery and ground. The service manual lists the possible causes as:
- High voltage harness or connectors
- electric compressor
- PTC elements heater
- traction motor
- On-board charger
- Li-ion battery
- DC/DC J/B

As you might imagine, troubleshooting all that is a chore and involves potential exposure to high voltage. As the service manual notes: "Touching high voltage components without using the appropriate protective equipment will cause electrocution"

That is a good idea to eliminate the aux battery as a culprit.

If that fails, then you could disconnect the HV connection to the PTC electric heater and retry; then d/c the HV connection to the electric A/C compressor and retry. Those are a couple of common items to have faults and are easy to check. All the other items in the troubleshooting list are more difficult to access.

12V: disconnect the aux battery from the car and make sure all cells have the plates covered and add distilled water if necessary; charge up and hold at 14.4 to desulfate the plates and get a full charge. Take it off charge and wait 1 hour with no load connection, If the aux doesn't read 12.8 then it is suspect. Or measure the specific gravity. Any added water gets turned into sulfuric acid during charging. If the plates are too sulfated then the damage is beyond the point of recovery. i use a Yuasa 1A charger to provide the 14.4 cycle after bulk charging with either a 3A or 10A dumb charger for larger batteries; i've tested many and it is the best and most accurate for voltage.

Thanks nlspace.

Can you point me to instructions on how to disconnect the HV connectors for the electric heater and A/C compressor?

On another thread a user said that the A/C low on freon can trigger error codes. Have you ever heard this?

My 12V is brand new as of 6 days ago. It has been draining little by little as I've been messing with the car, now reads 12.1V with car off, drops to 11.7 with it on. I'm assuming it's still in good shape and should take a charge. I don't have a charger so I'll use my other car to jump it. How long would you expect it would take with 14V from the other car (running) to give it a good charge?

danbertolet said:

I don't have a charger so I'll use my other car to jump it. How long would you expect it would take with 14V from the other car (running) to give it a good charge?

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Perhaps now is a good time to get a charrger. With a jump cable, I don't think you can count on more than very roughly 20A into the low battery, so it would still take about 2 hours to charge from flat (and 12.2V with no load is very flat). The actual time depends on so many things, like the quality of your jumper leads (some are more plastic than copper), how good the connection is at both ends, etc.

Perhaps now is a good time to stop chasing what is obviously not a 12v issue before the OP electrocutes himself!
Sorry, but these are the sort of things you need to pay a shop/dealer/whatever to fix (as painful as that may be).

Stanton said:

Perhaps now is a good time to stop chasing what is obviously not a 12v issue

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Perhaps you are an expert at diagnostics, troubleshooting and repairs, so i would like to hear your basis and evidence for such a conclusion.

From the limited data that i have read it seems that now there really is an auxillary battery issue which must be corrected before any additional troubleshooting is possible.

12V is brand new as of 6 days ago. It has been draining little by little as I've been messing with the car, now reads 12.1V with car off, drops to 11.7 with it on.

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danbertolet said:

...
On another thread a user said that the A/C low on freon can trigger error codes. Have you ever heard this?...

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I don't know if low freon would trigger that code, but I do know the electric compressor requires a specific lubricating oil that maintains its dielectric properties under high voltage. If someone "topped off" the refrigerant with a product containing the wrong oil that could cause problems.

Perhaps now is a good time to stop chasing what is obviously not a 12v issue before the OP electrocutes himself!

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With 13 volts...?