My Volvo V70 had thrown the P0442s EVAP small leak code and after checking gas cap, J-tube and not being able to fix it, i took it to the local independent Volvo guy. To my surprise, the error code morphed, he said he only could find a P0032 code. That is actually the only symptom that something is wrong, the "check engine" light, the car runs smooth, averages 24 mpg in city and i just returned from a 700 mile road trip where it averaged close to 30 mpg. I have already spent a morning inspecting vacuum hoses in the engine and could not find any problem.

Should i still check the oxygen sensor heater? I see four wires attached to it, green, yellow, blue-red and green-red, which ones are the heater wires and what checks can be done in the car without removing the sensor?

thank you in advance for your help?