P0AA6 and P31E7 on a 2018-2021 Nissan Leaf: Won't Restart? Find the Leak to Ground First

P0AA6 on a 2018-2021 Nissan Leaf means the control module read high voltage insulation resistance at 250 kilohms or less, a leak to ground, and P31E7 follows to block restart. The cause is the compressor, PTC heater, inverter and motor, PDM or battery pack, depending on when it sets. Confirm it by running five operating states with a scan tool. A car that is shut off may not restart, so find the leak first.

What does P0AA6 mean on a 2018-2021 Leaf?

P0AA6 (HV battery voltage system isolation, sub-code 1A) is a low insulation resistance fault: current leaking between the high voltage side and vehicle ground. The Li-ion battery controller sends the pack's insulation sensing signal to the control module (VCM), which watches the high voltage circuit from it.

The VCM sets P0AA6 when the reading is 250 kilohms or less in any of five operating states:

• READY, shift in P, A/C off, for at least 50 seconds.
• READY, shift in P, A/C full cold, for at least 30 minutes.
• READY, shift in P, A/C full hot, for at least 30 minutes.
• Shift in D, faster than 10 mph (15 km/h), for at least 40 seconds.
• Power off, quick charge connector connected, quick charging for at least 20 seconds.

With the power switch on, once the VCM has detected P0AA6 it sets P31E7 (restart inhibition). P31E7 has no signal, threshold or delay of its own.

Each state points at a part: A/C cold at the compressor, A/C hot at the PTC heater, driving at the inverter and motor, quick charging at the PDM. Idle with the A/C off points at no single part, so you work through the harness and components by elimination. A leak between the quick charge relay and port, or between the normal charge port and the PDM, does not set P0AA6.

Both codes are one trip (power switch off, then on). The VCM requests the EV system warning lamp through the combination meter over CAN. P0AA6 blocks quick charging, normal charging and another READY start; P31E7 blocks another READY start.

Three sibling codes set from the battery controller and only light the lamp: P33DF (isolation sensor signal voltage too high, delay 20 seconds or less), P33E0 (too low, delay 20 seconds or less) and P33E1 (no amplitude variation in the signal voltage). The pack inspection below applies to P33E1 as well.

What symptoms does P0AA6 cause on the Leaf?

• EV system warning lamp on.
• Quick charging will not run.
• Normal charging will not start.
• The car cannot be put into READY again after power off ("Service EV System").

What causes P0AA6 on the Leaf, most likely first?

This is a working order by part, because the fault follows whichever part is leaking.

How do you diagnose P0AA6 on a 2018-2021 Leaf?

You will need a scan tool with EV self-diagnostics, an insulation tester, a voltmeter rated for high voltage work and insulating gloves.

What if the obvious fix does not work?

Revisit the refrigerant history. Other gas mixed into the system can lower insulation, and a new compressor will not cure that, so change the refrigerant and oil.

After the code is cleared the car can run again for a while and then throw the fault again, so a cleared code does not mean the cause is gone. Check the 12 V battery too; the confirmation runs need it at 11 V or more.

Your stop point is the idle branch. If the harness side fails and the compressor, PDM, motor and inverter all pass, replace the harness between the PDM and the pack. If the pack inspection turns up nothing, replace the battery controller.

How do you confirm the repair?

After any repair, reconnect everything, power on and erase the DTC. This is required. These are required when they apply:

• After installing a compressor, use only new EV compressor oil (never recovered oil), replace the O-rings, run it in READY with A/C on for at least 1 minute with the car parked, and check its electrical bonding to the body.
• After replacing the motor or inverter, write the traction motor resolver offset with the scan tool. After an inverter swap the warning lamp comes on and P325C-00 sets until this is done; check the lamp is off and erase P325C-00.
• After replacing the Li-ion battery or battery controller, run the gradual capacity loss data clear (never on a part that was not replaced with a new one) and load the battery identification data, otherwise P3102 sets.
• After replacing the junction box, run the junction box data clear.

Then repeat the five states, each starting from power off, a 90 second wait and a 12 V battery at 11 V or more: READY in P with A/C off for 50 seconds or more; A/C full cold for 30 minutes or more; A/C full hot for 30 minutes or more; drive in D above 10 mph for 40 seconds or more at a safe speed; power off and quick charge for 20 seconds or more. If P0AA6 does not return in any of the five, you are done.

If other codes are stored, work them one at a time in priority order. P0AA6 is in group 2 and P31E7 in group 3, so group 1 comes first:

• The communication and CAN codes are B1921; U1000, U1001, U1010; U1073, U1074, U2155; U1009, U100B (quick charger communication); P318D, P3191, P3193, P3194, P3195, P3196, P3197, P319C, P319E, P319F, P31A0, P31A1, P31A2, P31A3, P31A7, P31A9, P31AA, P31AB, P31AD, P31AE, P31AF, P31B0, P31B2, P31B3, P31B4, P31B5, P31B6, P31B7, P31B8, P31BA, P31BB, P31BF, P31C3.
• The quick charge codes are B2801, B2802, B2803, B280A, B280B, B2814, B2830, B2880, B2980.
• The control module and reference voltage codes are P0603, P0643, P0616, P3175, P31C5, P31C6, P31C7, and every other VCM code except P3101-62.
• The sensor codes are P1551, P1552, P1556, P1557, P2122, P2123, P2127, P2128.
• The crash detection codes are P3135, P3137.