Subaru XV Crosstrek Forums banner

Anybody else having Front Oxygen Sensor Issues?

9K views 15 replies 13 participants last post by  VaCross2018 
#1 ·
Has anybody else had to replace their front oxygen sensor recently?

A couple of months back my car dropped into limp home mode while I was driving on the interstate. A little disconcerting but my XV kept chugging along albeit with much reduced gas mileage.

I took it straight to my local Subaru specialist and they couldn't figure out what was wrong with it. They finally called the local Subaru dealer to see if they could get any clues and decided it had to be the front oxygen sensor.

I didn't have the resources at the time to get that replaced and just followed their recommendations to use top tier, mid grade (89 octane) gasoline until I could bring it back in for a replacement with the strong warning that I was shortening the life of my catalytic converter the longer I waited.

In the three months I drove on the "failed" front sensor the car never dropped back into limp home mode again but the fuel economy never fully recovered. (The 28.8 mpg highway driving including the expected drop associated with winter driving.) I also purchased an ODB II bluetooth reader and app to monitor performance on my phone. Sure enough, O2 sensor #1 was ready nothing....

So, I finally took it back in to get the oxygen sensor replaced and viola! Fuel economy recovered dramatically....for about 8 days... then it tanked again. Still no limp home mode but another look at the ODB II and sure enough the O2 sensor is reading nothing.

I am going to double check my tire pressure and my intake air filter in the mean time....

What is the typical impact of temperature on mileage for you all?

Have any of you had similar issues?
 
See less See more
#2 ·
Recently, my local Subaru mechanic informed me that the caked-on mud around the catalytic converter and oxygen sensor are not to be left like that, as it may have an adverse effect on the readings.

I'm assuming corrosion and other materials around the O2 sensor may have played into your current predicament.
 
#3 ·
Yeah, I've had to frequently drive across a salty winter pass. I've made a habit of thoroughly washing the car after each trip but that's just a mitigating tactic really.

Interestingly enough, I took by the shop and they showed me that the new front O2 sensor appeared to be running just fine. My bluetooth ODB II sensor wasn't reading the constant voltage signal I guess as well as confirming that I am a bit of a car hypochondriac.

They kept trying to get me to run midgrade but I've found that using it induces both a metallic pingy rattle upon acceleration and leadens my right foot.

Also, signing into to Fuelly helped reset my mileage expectations. What an awesome amount of data....
 
#4 ·
You should be able to run regular fuel and not hear any "pingy rattle" while accelerating.If you must run mid grade or premium fuel to eliminate that ping/rattle then you have a problem with pre ignition.The knock sensor isn't detecting that ping/rattle.If it did then the ECU would have retarded the ignition timing making the plugs fire later to stop that ping.I would say the issue lies in the knock sensor,the ECU or the connection between the two.
 
#11 ·
I know this thread has been dead for awhile, but I am having the same issue. Sudden dip in MPG and zero volts on O2 sensor 1 from my OBD tool. No check engine light.

I decided to replace the O2 sensor myself, but the threads stripped on the way out. Waiting for an O2 sensor thread chaser to see if I can get the new one in properly.

Anyone else have similar problems or problem solved with new O2 sensor?
 
#6 ·
The recent loss of mileage thing could be the switch over to "winter" gas. But it should be a fairly minimal amount overall- maybe 2-3 mpg possibly more depending on your driving habits.
They usually start distributing the winter stuff around 1st of October or thereabouts. Might be earlier in colder climates.
 
#8 ·
I’m running lean.. according to my obd2 readings I’ve printed out since March 2020 its been lean.. doh ! So picked up an 02 sensor for front and set to replace the old .. ¯\(ツ)/¯ was hoping for tips on doing that. Looks easy enough from top down.
tho I’ve seen service manuals say to lift the vehicle,, blaa blaa - well i ain’t got no lift , no pit - just i ramps i use for oil changes and floor Jack and Jack stands which seem awfully tall at the lowest setting to place under .. uggh
 
#12 ·
Howdy folks of the past, I recently purchased... well financed rather a '17 Crosstrek premium cvt. Shortly after getting the car a CEL appeared with flashing cruise light. I promptly acquired obd sensor (fixed) and found a code P0420. Shortly after I took it to the shop(as it was running somewhat poorly and has gradually degraded to a stated easily comparable to hammered sh*). A decision I regret immensely as naturally 'its the catalytic converter' of which they charged $1200 for the part and another $400 for labor and w/e else. Not a day passed and CEL reappears. I drove about a week and cleared code 3 times before returning to the shop. The mechanic who performed said 'repair' seemed upset that I would return with this concern and proceeded to have me ride passenger while he hailed donkey d** through the parking lot.. I was impressed as I hadn't even attempted to speed in the car at that point. Anyhow, flash forward to today and the car has continued to decline in performance. I can only assume it is the corresponding o² sensor. And tbh the mechanic even said shamelessly that there was an oil leak directly on said sensor. But it appears to be super easy to get to so I will replace it as soon as my pocket book can manage and will report back with my findings.

Stay safe(and spooky) out there,
Spud
 
#13 ·
My college age son is having exact same problems with his ‘17 Crosstrek. Catalytic converter replaced under warranty. Paid for new oxygen sensor and air mass sensor. Codes are still coming up as running too lean. The car is now at the dealership to try to resolve this before heading back to college. Did you ever get your problem resolved? His gas mileage has been TERRIBLE!!!!
 
#14 ·
I would look into that O2 sensor and air mass sensor being covered by a federal emissions warranty if car is under 80k. I just learned about this warranty last week, it is for most emissions related parts for up to 8 years/80k miles. I just had my rear O2 sensor replaced and it was covered by the federal warranty, I had to find out about the warranty, they just wanted me to fork over $600 to replace the sensor. And if it is covered for your car, I'd be getting a refund from the dealer. I'll also say that I've learned that at times this can actually be the ECU that has the issue.
 
#15 ·
Excellent advice. I read up on the Fed emissions coverage several years ago, when my local Toyota dealership tried to charge my wife 55.00 for a defective gas cap, AND a diagnostic fee. I phoned the service manager while she was still there and he removed the charges. Claimed the service advisor was unaware of the Fed emissions warranty coverage for the replacement cap:sneaky:. Anyway. New cap, no codes. No charge.
 
Top