Should the front o2 sensor be replaced only when the CEL goes off or after they start to get old?

 

I'm pretty sure my 97 Legacy 2.2L has the original O2 sensor and 135K on it.

 

Also, anyone know what the OEM brand is? Bosch? Denso? How are the other aftermarket brands on these (I'm looking at NGK/NTK and Delphi)?

 

Thanks!

After 135K if you want to you can, but usually you wait for a performance issue or for the light to come on, which can be NOW, nope not now, maybe tomoorow, maybe next year ....

 

Use OE for the front. I usually wait for an issue of it throws a code.

Which code is it that usually signals the death or dying of the front O2 sensor? Is it a 420?

Yes the ever popular or poop - u - lar 420

For the front it can also be the oxygen sensor slow response code, I think that is P0133.

If your original front 02 sensor lasted 135k miles, you did well. Here are my notes for front 02 event:

>> My fix turned out to be the front 02 sensor. I have a 2001 Forester L with 85k miles on it. I have been chasing an intermittent hesitation under load problem for the past year since 80k miles. Only occurred when engine was warm. The front 02 sensor had been replaced once at 40k miles. I suspected it again this time, but since the only codes thrown had been cyl's 2&4 misfire (p0302 & p0304) I assumed it must be ignition related. So I replaced plugs and wires 8 months ago...no effect. Did the dollar bill test over exhaust pipe, it was fine. Misted the coil, no sparks. I mentally sort of ruled out the fuel filter since it only happened when the engine was warm. Finally, a week ago while cruising on hwy at 65 mph, I felt the hesitation again (I wasn't even accelerating this time) and a new code was thrown....p0172 (bank 1 too rich). AutoZone read it for me, I described the symptoms to the guy and asked if he thought it might be the front 02 sensor. He said, "absolutely." So I decided to replace it next. Cost me $100.75 incl tax for the oem part# 22791aa00a from Cityside Subaru. I asked the Parts guy there if his experience was that this model engine needed a new front 02 sensor every 40k miles. He said, "no, these sensors are good for 100k miles." Well, bullsnot on that. I replaced the new front 02 sensor in 1 hour reaching from the top over the passenger side of the engine using an adjustable wrench. Be sure to use the thread lube so you can get it out easily next time.....after another 40k miles. I took out the air channel assembly first for better access. That seems to be the fix. No further hesitation since. Car runs like new. Replaced on 6/2/7 with 84,922 miles. >>

Thanks all. I think I will hold off for now as the only symptom I'm experiencing is poor gas mileage on highway trips under 15 miles (19-20 mpg vs high 20s on longer trips).

Should the front o2 sensor be replaced only when the CEL goes off or after they start to get old?

 

I'm pretty sure my 97 Legacy 2.2L has the original O2 sensor and 135K on it.

 

Also, anyone know what the OEM brand is? Bosch? Denso? How are the other aftermarket brands on these (I'm looking at NGK/NTK and Delphi)?

 

Thanks!

 

There is good reason to replace it before it is so dead it triggers a code.

Thier reaction time slows w/use,thus measuring mixture less accurately w/time.

Unfortunately,reaction time(crosscounts in techno speak) is difficult to judge w/garden variety backyard mechanic tools.

 

How long to leave the old one in? Good question.I think sensor life is highly variable and depends on the amount of contaniments seen internally and externally.

 

Increased fuel use could be a sign of a tired non code throwing sensor.

 

I thought someone said OEMs were Bosch.

I`d use the cheapest.

I don't know the usual life for oxygen sensors on Subarus, but they have typically lasted 90,000-120,000 miles on my other cars. I replaced the upstream oxygen sensor when I replaced the timing belt on my 2006 Forester. With the timing belt off, and the radiator out, the oxygen sensor was just sitting there fully exposed. It looked like I could practically unscrew it with my fingers.

 

The oygen sensor looked like a real PITA to remove when the engine was fully assembled. So, I replaced the sensor at 105,000 miles. I plan on selling the car at 200,000 miles hopefully it will last to then.

I hope you don't mind if I piggy-back on this thread.

 

Our 2003 Legacy is throwing a P0132 code (or is 133?) I have a scanner and watched the voltage on the upstream sensor and it was perfectly flat at 2.158 V. Does this mean that thing is dead? Shouldn't I be seeing it switch up and down between .2 and .8? I am going to go out and run it, then pull a vacuum hose to see if it wavers at all.

I hope you don't mind if I piggy-back on this thread.

 

Our 2003 Legacy is throwing a P0132 code (or is 133?) I have a scanner and watched the voltage on the upstream sensor and it was perfectly flat at 2.158 V. Does this mean that thing is dead? Shouldn't I be seeing it switch up and down between .2 and .8? I am going to go out and run it, then pull a vacuum hose to see if it wavers at all.

 

What do you mean by scanner? An oscilloscope?

What do you mean by scanner? An oscilloscope?

 

Snap-on Solus Pro.

So is Bosch really the OEM? Or is it Denso?

So is Bosch really the OEM? Or is it Denso?

I replaced mine (97 Legacy L) last night. I thought it was a Denso, but the sensor I pulled was a Bosch. My housemate thought his 02 WRX had a bosch sensor, but he pulled a denso.