Hello i got a question about my 1992 volvo 240. Whenever my engine was up to operating temp, check engine light appeared on the dash, i got code 2-1-2 wich means O2 sensor. All the wires from O2 up to fuse 4 up to fuel pump relay are good but im getting no 12v on the entire heater circuit. O2 sensor works as its a completely new one.
But today i found out if i connect 12volt from fuse 13 (heated seats wich i dont have) to fuse 4 (fuse for O2 heater circuit), the light stays off and the car runs completely fine. Any ideas?
i also have 0 idea where the circuit originally gets its 12v from, i thought maybe fuel pump relay?

 

Check the wiringand the fuse box.
Also, check the vehicle's grounding points. Poor grounding can impede the flow of electricity and cause voltage problems.

 

Dude, you are flying blind if you don't download the Volvo manuals from https://ozvolvo.org/archive

 

I’ve checked al wiring and the fuse, the check engine light keeps coming on again all of the sudden.
Ive measured the o2 sensor signal wire and it doesnt fluctuate at all, it stays at 0.40v and doesnt move, the o2 sensor itself is brand new. Im kinda stuck idk what to look for next.