Oxygen sensor, bank 1 sensor 1, 2004 Endeavor
 

Am getting engine code P0135, so thinking this sensor is bad. How big a job is it to replace this sensor? Does the plenum need to be removed to get to it?

Also, is it common for O2 sensors to fail prematurely on this model? Vehicle has 76K miles. Bank 2 sensor 1 had to be replaced at 62K miles. This is beginning to annoy me.

Thanks in advance for any advice.

It does seem to be very common for oxygen sensors to require replacement. I wonder whether this is caused by bad fuel causing them to fail. Possibly carbon deposits. Maybe over filling the oil?

One person in the forum said they only cost about $30. My Mitsubishi Pajero/Montero in New Zealand appears to have only 2 sensors (one for each bank) but I think my son's Endeavor in the USA has 4 sensors with two on each bank. Since the Endeavor had a cross mounted (East-West) engine the back sensors may be more difficult to replace. the Montero has a similar engine mounted straight (North-South) and is easier to work on. You might want to replace all four to save future hassle?

I just got my O2 sensor from Rock Auto and it was like 32 bucks compairing to Advanced Auto in my neighborhood that was 78 bucks as well as 5 other local stores so it may be best to order online for an O2 sensor.

Thanks for the replies. I don't know what causes these sensors to die, but it's a bit aggrevating. I use premium fuel, change the oil and filter every 4000 miles and have never overfilled the oil.

Since the bank 1 sensors are on the firewall side with very little room to work, the plenum may need to be removed (I was hoping a tech could ring in on this for me), in which case it might make sense to replace both bank 1 sensors as well as the spark plugs. As far as the cost is concerned, it appears that aftermarket sensors run around $70, which isn't too bad compared to almost $225 that the Mitsubishi shop charged for the part alone when the bank 2 sensor failed a couple years ago.