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Tuesday, 17 July 2012

Subaru Outback O2 sensor replacement...

In a previous post I mentioned how I had managed to diagnose a check engine light on my 2005 Subaru Outback and tracked down the fault to a burned out heater coil in the front o2 air/fuel or lambda sensor.

After baulking at paying $530 for the official Subaru part I tracked down a compatible Denso sensor part number 234-9015 on ebay for only $110 shipped from the USA. Then it lay around on my shelf for a month or two, as I actually had no idea where this part was supposed to go.

I didn't have a service manual, so I watched a few you tube videos, and read some forum posts, then finally got under the car and had a look. Finally I saw what looked like an O2 sensor, it was on the exhaust system as expected, but there was barely any room under the car, and it looked like I needed a special tool- a 22mm O2 sensor wrench to remove it anyway. I duly ordered the tool from ebay for $17, then one Sunday afternoon parked the car with the drivers side wheels up on the kerb so I could squeeze under the car and replace it.

I came off easier than I expected, but it looked a little different to my replacement part. Never mind, I plugged it in, also noticing that although the plug fit, the connector was not quite the same either, and would need to be taped to hold it together.

It wasn't till I started the car and checked the OBD codes on my Mac with the excellent Movi software that I realized the damn error codes were still present... only then did it twig that I had mistakenly replaced the rear O2 sensor!!! Finally, I located the front O2 sensor, but it was up near the drivers side wheel obstructed by the plastic engine undercover, and looked like it would be a real pain to replace from  under the car, as it would involve removing the engine undercover. After much cursing, I swapped back the original O2 sensor, incredibly glad that I didn't remove it by cutting the wires, and resolved to pay my mechanic to fit the replacement sensor a my next service.

But it actually turned out easier than I expected - I opened the bonnet and removed the air intake duct that goes into the air filter so I could get a better look and observed that it was quite possible to remove the O2 sensor without having to muck about under the car. It was about as hard as replacing a light bulb, then all I had to do was clear the codes and BAM! No more annoying engine light and flashing cruise control indicator distracting me on the dashboard.

So all up it cost me $110 for the part, $17 for the tool, $20 for an OBD code reader and $50 for the software... all up $197 instead of $530 for the official part, plus labor.

So awesome, I blogged about it...


  1. Thanks so much for that info. I'm going through the same thing with my 2005 Outback. Can I just clarify something -- are both oxygen sensors the same? ie. you bought one that fits both the back and front?

    I know I need a new sensor (mechanic told me that's what the codes were), but didn't specify which one. I was thinking of buying one if it would fit both positions, then it's a 50/50 chance. Otherwise, I'd need to figure out which one to get the specific model.


  2. Hi, best thing to do is buy an OBD code reader from ebay.... shouldn't cost more than $30 tops.
    That will tell you which o2 sensor is fubar. they are different sensors- the cable connection is different - but they will both screw into the same socket so I guess in that respect they are the same. The top sensor is really easy to replace... the bottom sensor you will need ramps to get under the car to replace it.

  3. Thanks a lot for your post.
    Have you had any troubles with using Denso replacement instead of Subaru original sensor over the course of 4-5 years (from the original post date)?

  4. since then the subie has had its engine replaced but the o2 sensor is still going strong