Oxygen Sensor replacement

Gannon · Post by **Gannon** » Wed Jan 19, 2011 8:09 pm

I just thought id post this up, in case anybody else has a similar problem.

Our recently acquired 04 Forester has had an intermittent "Check Engine" light showing up.

I took it to the auto electrician to check the codes, their machine came up with nothing, even though the CEL was still on.

So i took it home and put my OBD2 USB adaptor back together (i had it apart trying to make it work with SSM) and plugged it in.

Code P0030 came up straight away. This means the front oxygen sensor isnt working.

So i did a little research (thanks to BobbyJimmy and Frog) and discovered that it isn't really a normal oxygen sensor, it is an 'Air Fuel Ratio' sensor and is somewhat like a wideband o2 sensor, but varying current as opposed to voltage in relation to A/F mixture. The heater circuit current is also controlled by the ECU to keep operating temperature constant.

After falling over at the $600 asking price for a genuine sensor, i hopped on the net and found several sensors with the same part number for around $150 USD, but these places would not post overseas. So i settled for $300 AUD and ordered it.

This afternoon it arrived, so armed with a 10mm and 22mm spanner, i unbolted the airbox and intake to gain better access and replaced the sensor.

Started up the car and CEL was still on. Grrrrr

Armed with the laptop and the OBD2 device, i plugged it in and clicked the "Clear Codes" button.... CEL gone.

I have since taken the car for several drives and all is good.

steptoe · Post by **steptoe** » Wed Jan 19, 2011 9:38 pm

Good work. Don't you love it when diagnostc systems work!OBD2 device not the one from jaycar? Wanna share ?

can recommend priceusa from bendigo or ballarat for go between non exporters and ourselves

rebuilder · Post by **rebuilder** » Thu Jan 20, 2011 1:14 am

dont yah have to just unplug the battery for a minute, to clear the ECU, then plug it back in and start, and it will relearn the situation.
If you just replace a sensor, and start the car, i think it waits 40 cycles (coolant at operating temp then back to cold) or something before it decided that the problem has been fixed.
Can anyone confirm this, i replaced my MAP/IAT sensor which had been throwing codes, and tested the theory, plugged new one in drove code came up for a second. turned car off, unplugged battery for a minute, plugged back in drove, and havent seen the light since. that was 2 weeks ago, and would be about 100 cycles since.