P0AA6: Hybrid/EV Battery Voltage System Isolation Fault
What to do
The car is designed to be safe with one fault — but you are now one fault from it mattering, so treat this as prompt business, not background noise. Do not touch damaged orange cabling or any high-voltage component, especially after a crash or flood; if the car has been in deep water, tell the workshop that specifically. A plug-in refusing to charge with this code is protection, not a charging fault. Qualified hybrid workshop only.
What this code means
The module has measured electrical leakage between the high-voltage system and the car's body — the isolation that keeps several hundred volts and the metal you touch strictly apart has degraded somewhere.
Why this is survivable at all is the design's first lesson. The high-voltage system floats: neither its positive nor its negative is connected to the chassis, so touching the body and one HV conductor completes no circuit. Electrocution needs two faults — which is why the module measures isolation resistance continuously and stores this code at the first one, while the system is still safe. The code means one of two barriers is gone, not that the car is live.
Where isolation goes is a short and honest list: chafed or crushed high-voltage cable insulation (underfloor cables on rear-motor cars lead this); water — flood exposure is the classic, and a hybrid that has been through deep water deserves this code's suspicion even without it stored; coolant finding its way into the electronics or pack; aged winding insulation in a motor (the P0A5D family's slow version); crash damage; and the repair-shop classic, a screw or trim fastener driven through a cable run. The measurement narrows it fast in qualified hands — isolation testers localise the leak to a branch of the system.
The vehicle's response varies from a warning lamp to refusing to charge (plug-in vehicles test isolation before every charge) to shutdown. Respect the code without fearing the car: the remaining barrier is real, and the do-not-touch rules below are about keeping it that way.
Likely causes
Start here
- Damaged high voltage cable insulation · specialist
- Water ingress into a high voltage connector · specialist
Less common
- Motor winding insulation breakdown · specialist
Rare
- Coolant leak inside the battery pack · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
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