Lambda sensor heater fault P0036

[G600]

I've got a code (no light) for the bank 1 after CAT lambda sensor heater, I've replaced the sensor with a bosch one and the fault still comes back as soon as I start the car, I've checked the wiring and the heater is getting power (peak 2 amps) I've run out of ideas, has anyone had the same problem? It's the M54b30 (pre facelift 3.0) engine.