[dahlgren]

Hi all,

getting P0135 from my ODB reader (O2 Sensor Heater Circuit (Bank 1 Sensor 1)):
- heater resistance 6 ohm, which seems reasonable (-> no open circuit, no short)

Disconnected O2 sensor cable, to measure O2 heater supply voltage without the load from the sensor:
a) ignition ON, engine OFF -> 3.8 volts
b) ignition ON, engine RUNNING -> 9.9 volts

Seems like odd values?
expected around 0 volts in case (a), and around 12 volts in case (b)...
supply wiring issue? or something I have missed?
Assume the heater power supply loop is controlled by the ECU somehow?
O2 sensor fuse checked/ok.
Is there possibly also a relay somewhere in the O2 heater power feed line?

Additional info:
engine code: B4204T
O2 sensor is 4-wire (yellow-black-white-red), heater on white/red loop.