Diagnose this O2 Sensor!

[BISCUT]

A new O2 sensor for my 06 Sentra is due in the mail today from Rock Auto. It was close to 40F instead of the low 20's we had this morning so I figured I'd get a head start and remove the old O2. This is original and has 161k on it. It is the upstream O2 sensor. I'm no good at reading the wear so I wanted to hear what the gallery has to say.

Check Engine was shining bright since I bought it at 159k and mileage was down by about 10 mpg.

 

[mattd]

Almost looks like a little bit of coolant residue on there. Is this a 1.8L?

 

[Jetronic]

well, if it's heated, measure the heater circuit resistance.

if you have a gas torch you can heat the tip with a voltmeter attached. That'll be a rich condition if the flame covers the whole tip. Remove from flame and the sensor should read lean immediately.

 

[mk378]

That's just a cover. The active part is inside.

You can't tell anything by looking at the outside cover unless the whole thing is burnt off then you'd know it is bad.

 

[BISCUT]

It is a 1.8. I just finished replacing it. Lots of room and so easy to install . Replaced with a Bosch. Have to connect the battery terminal and go for a ride. Interested to see if this corrects the horrible gas mileage condition.

 

[BISCUT]

Almost looks like a little bit of coolant residue on there. Is this a 1.8L?

No coolant weeps or leaks that I can see. I looked up some images online but who knows. Figured post up a pic and see what those in the know have to say.

 

[Jetronic]

looks like the car might have run lean, from the white colour. possibly due to failing o2 sensor

 

[The Critic]

Almost looks like a little bit of coolant residue on there. Is this a 1.8L?

Definitely coolant residue. And HG's are not exactly stellar on 1.8L's.

 

[Kestas]

At 165K I don't know if it's worth thinking too much about it. But I understand you want to get to the bottom of your gas mileage issue.

BMW specifies O2 sensor replacement every 100K. I follow this for most my cars.

 

[BISCUT]

I did a drain/fill with Pentofrost 2 about 1k miles ago and am losing no coolant thus far. Connected the battery back and the check engine light is now off. Drove it to drop off one of the kids at baseball, just under 40 miles to and from. Much smoother for sure. I'll have 300 miles by Thursday to be able to check the mileage.

She should be purring! Radiator drain/fill; plugs; oil & filter change; PCV changed. Hoping for Strupt, shocks, tires and ride her to the grave!

 

[BISCUT]

looks like the car might have run lean, from the white colour. possibly due to failing o2 sensor

I'm under the belief from the seller the light has been on for a while.

 

[350Rocket]

I did a drain/fill with Pentofrost 2 about 1k miles ago and am losing no coolant thus far. Connected the battery back and the check engine light is now off. Drove it to drop off one of the kids at baseball, just under 40 miles to and from. Much smoother for sure. I'll have 300 miles by Thursday to be able to check the mileage.

She should be purring! Radiator drain/fill; plugs; oil & filter change; PCV changed. Hoping for Strupt, shocks, tires and ride her to the grave!

It's been a while now (over 10 years) but the only vehicle I have owned that I changed an o2 sensor on was my 89 caprice, I was driving it 222kms a day to work and back, it used zero coolant but the o2 sensor had that greenish look to it like yours.

Unfortunately in my case the o2 sensor replacement had no effect on fuel mileage or anything. I just did it because it had 300k miles and may have been original.

 

[mattd]

Definitely coolant residue. And HG's are not exactly stellar on 1.8L's.

Exactly what I was getting at. OP hasn’t noted what engine yet though.

 

[BISCUT]

I apologize, I thought I said 1.8 but I did not. I'll do a closer inspection for weeps. Any specific area the 1.8's tend to leak from? I would think I'd notice some difference in coolant level. I'll keep checking. The car isn't sluggish either and when I changed the oil and filter it wasn't milky; no white smoke in the exhaust at start up.

 

[mattd]

You’d notice it after sitting over night. A small stumble, small puff of smoke. I would pull the plugs when it’s dead cold and pressure test it and see if you see any coolant on the pistons.

1.8s are common for head gaskets. The only way traces of coolant ends up on an o2 sensor is being burned in the engine.

 

[BISCUT]

She's a keeper! Had to run to another state to pick up a speciality head for a acid neutralizer I use in my home. 160 Mile round trip. Stopped at the gas station just before I got home and hand calculated 34MPG. Considering it was about 18MPG me thinks the O2 sensor was indeed gone!

It was 25F this am and no smoke from the tailpipe on start up. I checked with a light and see no external signs of any coolant weep. No temp gauge fluctuations and smooth idle and acceleration. So I'm hopeful the HG on this particular 1.8 is a ok.

 

[The Critic]

I apologize, I thought I said 1.8 but I did not. I'll do a closer inspection for weeps. Any specific area the 1.8's tend to leak from? I would think I'd notice some difference in coolant level. I'll keep checking. The car isn't sluggish either and when I changed the oil and filter it wasn't milky; no white smoke in the exhaust at start up.

You won't get white smoke until the failure is catastrophic. Small seeps will usually show elsewhere - often misfires. Try pressure testing the cooling system when it is cold and pull the plugs as suggested.

 

[BISCUT]

You won't get white smoke until the failure is catastrophic. Small seeps will usually show elsewhere - often misfires. Try pressure testing the cooling system when it is cold and pull the plugs as suggested.

I pulled the plugs a few weeks ago and changed them out. No coolant or oil was seen. I did not pressure test anything though.

 

[350Rocket]

You won't get white smoke until the failure is catastrophic. Small seeps will usually show elsewhere - often misfires. Try pressure testing the cooling system when it is cold and pull the plugs as suggested.

Coolant level will drop over time also though if there is a coolant leak, which he said wasn't happening. Like I said I had another vehicle that I was driving 222kms a day, was not losing any coolant and the o2 sensor looked weird and greenish. It was also likely original with 300k miles and 20 years old.

 

[BISCUT]

After battery reset and new O2 upstream the check engine light came back on. I get 2 codes. One is EVAP (Po455 8) and may be due to the gas cap not seeming to fit correctly. New gas cap ordered.

Second code is P2A00 0 Bank 1 which is 02. My gas mileage is 31 mix and 35 highway so it's working. Bank 1 is upstream and Bank 2 would be the downstream O2 correct?

Surprisingly there were no other codes on the complete scan. I figured there would be a few!