guido said:
Apparently me heating sensor of the O2 system stays on when the engine is not running. The only way to get it to turn off/cool down is to switch the battery off. Has anyone experienced this? Yamaha 150 ox-66 saltwater series.
Quite unusual.
I wonder how you found out it is powered. I would suspect that other electronics on the motor might have power also.
One thing I would check is to remove the connector and measure the resistance between the motor metal and each lead of the heater on the sensor. There should be high resistance. If the resistance is low, it tells me that the heating coil has shorted to the casing.
Another step is to measure the voltage at the wire side of the heater with the sensor unplugged.
I would expect that if you measure 12 volts across the two leads, something is wrong. I think the ecu works by grounding devices and 12v is always there. If you measure 12v across the leads either there is a short to ground in the harness or the ECI is bad.
I am also not sure if there is a power relay. I am looking at the schematics but haven't found one yet. If there is, it may be stuck closed. I will continue to look.
Update, there is a main relay in the main junction box. It could be bad
