hi i have and engine light on my ford fiesta mk6 1.4 petrol. so i used an obd2 reader to find that the fault is p0030 which is the o2 sensor heater circuit in bank 1 sensor 1. i thought i needed a new sensor but i checked the resistance in the o2 sensors two white wires (not sure if correct) and there is resistance. so now im thinking its an electrical issue but im not sure what to do next as i cant find a bad fuse and i cant find a diagram for the wiring.

any help would be much appreciated.

is there another fuse box in the engine compartment that im not seeing maybe?

Start the engine and see if you have 14v ish on one of the wires to the o2 sensor

What resistance did you get?

i think it was around 0.09 but i shall check again tommorrow.

Have you tried clearing the fault and seeing if it comes on again?

You'll probably struggle to work out what's going on with the resistance readings on the hego sensor unless you've got the specifications to compare to from Ford or Haynes manual etc.

If the fault doesn't come up again after clearing it then leave it at that - I've seen this kind of fault come up on my last ST (and maybe this one) only in winter and usually when the car had been driven very very gently for a while such as you would if road conditions were bad due to heavy snow etc.

yea i have tried clearing the fualt.

i get around 10 ohms of resistance on the heater circuit ( is this too much?)

and i got just over 14v on the wire to the sensor.

should i just replace the sensor?

or take it to a garage or ford?

or any other suggestions?

Does it give the same fault if you disconnect the sensor?

Info on the web says you can get a health reading of the sensor by measuring it's resistance, example here

http://ngkntk.co.uk/index.php/technical-centre/lambda-sensors/how-to-test-lambda-sensors/

If you're on the correct wires and getting 10 ohms then this is an ok reading according to the ngk info.

If the last resort is to change the sensor you'll probably need a lambda socket to remove your old one, and have a good look on the web first as you can often source the exact part much cheaper without going to a Ford dealer.

okay so ive ordered a new sensor. but just after I decided to, just on a whim, swap two of the fuse box relays (one marked for engine) and remove the codes again and surprisingly after a few restarts and a short journey it hasn't come back on. I'm not sure if it's because of the relays or just a coincidence but fingers crossed it stays off. but maybe it was because the engine was already warm and it will come back tomorrow but we will see i guess.

thanks for your help guys