Replacing front o2 sensor - V7 WRX STi

[Scoobydoo]

Okay so I was getting a CEL and found out it was the front o2 sensor - one that controls air/fuel ratios. I don't know what the error code is any more, but I found it by getting it scanned with an obd2 reader.

Anyway, I found out what replacement to get and sourced it via eBay, as it was 1/3 the price of buying one locally.

The sensor is located in the front exhaust manifold, just before the uppipe. There is a heat shield surrounding it so you have to undo that - 4 x 14mm bolts.

The wiring goes up the side of the engine and is the top connector here:

It is connected via a metal bracket, which is bolted down using the bolt for the coil pack. I had to take out the air filter box to get at it but it was easy enough to undo.

At this point I was kinda stuck. I could see that I had to get something on the sensor to turn it out, but the hex nut was too far under the heatshield to access it, I wasn't able to get anything on it. I tried polygrips on the sensor but since it's smooth I had no luck. So I did the next best thing - attacked the heat shield with a die grinder with a thin grinder blade on it. After a while I finally cut through it.

The steel was too thick to bend and in such an awkward place that I had to do this twice, which worked out easier in the end as I was just able to slide it on and off

The sensor requires a 22mm spanner. Either by good planning on Subaru's part, or good fortune on anyone else's part, the ring fits over the plug so you can slide it down the wiring and over the sensor. Excellent! This also means you can do the "spanner on spanner" trick to get more leverage. I had to do this.

Old vs New

New plug installed

Just like a bought one

Whole process from start to finish took about 90 mins. Was pretty easy to do, but I know that sometimes can really weld themselves in tight. I guess I was lucky.

[Jambun]

reckon you could fit stilsons in there?

[WRXONP]

hey man... i just realised what the spare plug in my engine bay is now because i run no front o2 sensor..

all though a tad off topic but still about o2 sensors

mines a ver 3 and they run the o2 in the manifold and also the o2 in the down pipe...

does anyone know if the front one is needed??

[WRXONP]

 Jambun said:

reckon you could fit stilsons in there?

stilsons to undo the o2 sensor?? you either a- fark the o2 sensor .... b- o2 sensors are usually dang tight to undo as the heat makes rust etc and makes it hard to undo... spanner is the best way to do it (ring end)

[Scoobydoo]

 Jambun said:

reckon you could fit stilsons in there?

Nah no way. I didn't know what you meant so I googled it. You couldn't fit much in there at all.

[Pappu1]

Good stuff bro

[Simon C]

It's a VERY tight fit in there. I had to get at mine from above, as my sensor is in a different place due to my aftermarket headers. Was a PITA to get at.

[Scoobydoo]

 Simon C said:

It's a VERY tight fit in there. I had to get at mine from above, as my sensor is in a different place due to my aftermarket headers. Was a PITA to get at.

Yeah you told me it was difficult but I forgot you had aftermarket headers. It was a rather painless job TBH.

[johnny5]

sticky this