fault code guideHybrid & EV
P0AA6: Hybrid/EV Battery Voltage System Isolation Fault
A safety sensor has detected electrical current leaking from the high-voltage system into the car's metal chassis. For your safety, the vehicle will shut down or refuse to start until a qualified technician fixes the leak.
How it shows up: A hybrid or electric system warning light will illuminate on the dashboard, often accompanied by the engine management light, and the vehicle may refuse to enter READY mode. An OBD scanner connected to the car will report fault code P0AA6.
Updated 10 November 2026
Can I keep driving?
Stop driving
High-voltage electricity is escaping its proper circuit, which creates a safety risk and prompts the vehicle computers to immobilise the powertrain.
What to do right now
- 1Pull over safely away from moving traffic, turn off the ignition, and apply the handbrake.
- 2Do not touch, pull, or inspect any orange high-voltage cables under the bonnet, underneath the vehicle, or near the battery.
- 3Arrange for roadside assistance to transport the car to a garage with high-voltage trained technicians.
Likely causes
Most likely first.
- Likely
Air conditioning compressor insulation breakdown
The electric air conditioning compressor runs on high voltage, and internal moisture, contaminated oil, or worn motor windings frequently allow current to track into the compressor casing.
- Possible
Coolant leak inside the inverter or battery
Conductive hybrid cooling fluid leaking from an internal pipe or damaged seal into an electrical housing creates an unintentional path for electricity to reach the car body.
- Possible
High-voltage battery internal deterioration
Electrolyte residue, terminal corrosion, or moisture ingress inside the sealed battery casing can bridge high-voltage current across to the metal outer shell.
- Rare
Damaged high-voltage wiring harness
Chafing against the chassis or damage from road debris can wear through the orange protective insulation and expose the internal conductor to earth.
What you can check yourself
Park somewhere safe and level, engine off, before you start.
- 1
Look for coolant puddles under the car
Inspect the ground beneath the engine bay and battery area for bright pink, blue, or green coolant puddles, but do not touch the underside of the car or any orange wiring.
- 2
Check the 12-volt auxiliary battery
A weak 12-volt battery causes computer glitches that can trigger false isolation codes. Check with a multimeter that the 12-volt battery reads at least 12.6 volts with the car switched off.
- 3
Check the boot area for moisture
High-voltage batteries are often housed under or behind the rear seats, so feel the boot carpet and spare tyre well for standing water caused by a leaking tailgate seal.
Rough cost to fix
Rough estimateTypical prices in Ireland (€) and the UK (£), from an independent garage up to a main dealer. Costs vary widely depending on whether the leak originates in an auxiliary component like the air conditioning compressor or inside the main high-voltage battery casing.
High-voltage electric air conditioning compressor replacement
- Do it yourself
- Garage job
- At a garage
- €950–1,850£800–1,600 in the UK
High-voltage inverter repair or replacement
- Do it yourself
- Garage job
- At a garage
- €1,200–3,200£1,050–2,750 in the UK
Hybrid or EV battery pack repair or resealing
- Do it yourself
- Garage job
- At a garage
- €1,400–4,500£1,200–3,900 in the UK
When to go to a garage
- Call roadside assistance immediately if the vehicle will not enter READY mode or stalls while driving.
- Book an appointment with a hybrid specialist as soon as code P0AA6 is stored, as this fault requires specialist depowering procedures.
- Do not drive the car if you detect a burning electrical smell or see liquid leaking directly from the battery pack.
Questions drivers ask
Can I clear code P0AA6 and carry on driving?
No, clearing this fault code will not resolve the underlying isolation issue. The car's battery computer tests insulation resistance before closing the main contactors, so the code and drive inhibitor will return almost immediately.
Can I get an electric shock from touching the car body?
The risk is minimal because the system isolates the battery pack the instant a small leakage is detected. However, you must still treat the vehicle with caution and never touch damaged orange cables or attempt to open high-voltage modules.
Will code P0AA6 cause an NCT or MOT failure?
Yes, on the UK MOT, this fault will cause an automatic fail because it illuminates the engine management light. On the Irish NCT, while isolation codes on their own result in an Advisory Pass, the vehicle will fail if it cannot enter READY mode to complete the inspection.
How does a garage determine where the leak is?
A qualified technician de-energises the high-voltage system using safety gear and uses an insulation tester called a megohmmeter. By disconnecting the battery, inverter, and air conditioning compressor one by one, they measure electrical resistance to locate the component leaking current.
Test rules here are for the National Car Test in Ireland (NCT) and the MOT in the UK. Elsewhere, check the regulations of your own country or state before going for a vehicle test.
The warning light you may see
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General guidance for most cars, not a diagnosis of yours. Details differ by make, model and year - check your handbook, and if in doubt, don't drive.