2020 Audi e-tron

Audi e-tron P0AA6 HV Isolation Fault — Battery Coolant Pump Leak

P0AA6 0xB20A12 Published 2024-10-30 Updated 2024-10-30
Audi e-tron P0AA6 HV isolation coolant pump battery leak J1J2

2020 Audi e-tron Quattro presented with P0AA6 and progressive coolant loss over 3 weeks. HV negative bus isolation 11 kΩ. Battery-dedicated coolant pump had a cracked pump body — coolant migrating into the HV battery underbody connector housing.

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The Problem
2020 Audi e-tron Quattro (72,400 miles) brought in with 'Electric Powertrain Fault' and P0AA6. Coolant reservoir had been topped off twice in the past 3 weeks by the customer. No visible external leak. P0AA6 and VW-group code 0xB20A12 confirmed via VCDS.
Diagnostic Procedure
  1. 1. Confirm P0AA6 and 0xB20A12. Negative bus isolation: 11 kΩ. Positive normal.
  2. 2. Negative bus fault. Systematically disconnect negative HV connections. After isolating the battery pack main connector (underbody): negative isolation jumps to >1.8 MΩ. Fault at battery pack connector or inside the battery.
  3. 3. Inspect battery pack underbody connector housing. Coolant staining and mineral deposits on connector faces. Coolant has entered the connector via a gap on the upper edge.
  4. 4. Trace coolant to source. Battery coolant pump (dedicated battery circuit pump, not HVAC) has a hairline crack in the pump body at the inlet fitting — coolant weeping at low pressure.
  5. 5. Pump is located 180mm above the battery connector. Coolant runs along a harness down to the connector.
  6. 6. Replace battery coolant pump. Clean battery connector with deionized water and compressed air dry. Allow 2-hour ambient dry.
  7. 7. Refill and bleed battery cooling circuit.
  8. 8. HV isolation: negative >1.5 MΩ. Clear P0AA6. Vehicle enters Ready.
  9. 9. Road test 30 miles. Coolant level stable. No fault return.
Resolution & Root Cause
Battery coolant pump replaced. Connector cleaned and dried. Isolation restored. P0AA6 resolved with no battery pack work required.
💡 Key Lesson
Audi e-tron P0AA6 with progressive coolant loss — locate the battery-dedicated coolant pump before any HV diagnosis. This pump is separate from the climate circuit pump and is located directly above the main battery HV connector. A cracked pump body (common on high-mileage 2019-2021 units) allows coolant to drip into the connector, creating the isolation fault.
About This Case

This case was solved remotely by an HVDesk specialist with 15+ years of hands-on experience across major EV platforms including Tesla, Hyundai/Kia, Volkswagen ID series, BMW i-series, and Ford EVs. The procedure was provided as structured remote support to an independent auto repair shop.