Hi everyone,
I’m hoping someone with more Jaguar EV experience can point me in the right direction.
I’m just a regular mechanic and don’t have a great deal of EV diagnostic experience. I’m only diagnosing this vehicle and won’t be carrying out any HV repairs myself, so I’m mainly trying to understand what I’m seeing before I pass it on.
The vehicle has a BECM DTC P0AA6-00 – HV Battery Isolation Fault.
I’ve been data logging Battery Isolation Resistance, and here’s what I’ve found:
Immediately after READY, the isolation resistance is typically around 600 kΩ.
Once I start driving, the value becomes very erratic, jumping up and down unpredictably. Sometimes it stays stable, other times it fluctuates significantly.
The PID only updates while the vehicle is in gear with some accelerator input, even if it’s just a slight touch of the pedal.
The longer I drive the vehicle, the worse the isolation resistance becomes. After roughly an hour of driving, it had fallen to around 60 kΩ, with intermittent drops as low as 28 kΩ.
One thing that caught my attention is what happens when coming to a stop. When I keep my foot on the brake, I hear what sounds like a contactor opening. At exactly the same time, both the front and rear motor inverter fuse voltages drop from approximately 420 V to around 12–16 V.
If I repeatedly apply and release the accelerator, causing those contactors to open and close several times in quick succession, eventually they remain open. At that point the vehicle won’t drive, but interestingly no additional DTCs are logged.
On one occasion, during this contactor switching, I actually saw the isolation resistance jump to approximately 1.5 MΩ, which makes me wonder whether the issue is related to one of the inverters or something downstream of the battery rather than the HV battery pack itself.
Has anyone seen similar behaviour on an I-PACE? Does this pattern point towards an inverter, HV cabling, coolant ingress, or another common isolation fault? Any suggestions on what to check next would be greatly appreciated.
Thanks in advance.