02 sensor replacements, no luck

i have a ‘05 4 cyl. Basic cab. With 120,000. I have had the downstream 02 sensor replaced 2 times in the last month. Both times I drive maybe 7 miles with a new sensor before the engine maitenance light comes on. The first replacement was a Delco, this latest one is a Bosch, no luck. I don’t think its faulty sensors although I’ve heard about that.

Anyone else have this problem? What could be the most likely reason? Wiring?

Frustrated!

Thanks.

 

Toyotas are generally not fans of Bosch O2 sensors... or at least they weren't a decade or so ago. Not much besides the odd Chrysler, Ford, or Euro vehicle that used them OE likes them either that I know of, so I don't have much current experience. But still... 7 miles means it's pretty much instant, as there are certain parameters that need to be hit to trigger codes that aren't straight up circuit issues.

What code(s) is it tossing out?

 

Maintenance light? You mean check engine light right? Did 2005s even have a maintenance reminder light?

Need codes to help you further

 

Bosch is trash for oxygen sensors, and Delco is not that great on Toyota either. Use Denso, nothing more or less unless you can afford OE.

 

Yes, I meant the check engine light. Also now I remember the sensor has now been change 3 times. The first 2 times it was a Denso sensor (not Delco, sorry for the confusion) I think my mechanic was trying the Bosch as a last resort to see if that might fix it. It didn’t.

Sorry I don’t know what exact code it is putting out. I was told that it is the code that indicates the downstream sensor is malfunctioning.

I think I might have to bring it to the dealer...

 

use OEM only


only thing that worked on my 4runner was stop trying to cheap out on sensors,
got the actual OEM ones, in toyota part number boxes, worked perfect and stayed perfect.

cost full price but...emissions system problems completely rectified

 

They'll probably say catalytic converter. Which it probably is. Did you change plugs at regular intervals or stretch them out? Old plugs can let the cat get clogged.

 

Sounds like you have a cracked manifold.

 

No, the plugs have not been changed. Good to know that the cat might be a problem. I will have them check. Thanks.

 

funny thing on my '99. still original cats.

sensor a/f front died around 130,000, rear o2 died around 140,000,
both replaced with OEM+nuts+gasket, still passing yearly state emissions tests
at >240,000 miles
and no codes, runs great. somehow my cats are staying clean, which is weird because when I raced 2-strokes for 5 years
I used trucky to consume my old 50:1 gas mix after racing (full tank + maybe 1 gallon 2-stroke, twice a month for 5 years)
probably helped it was motul synthetic 2-stroke oil

 

thats great that yours are still going strong.
As long whatever is going through the engine is getting burned completely the cats will be ok. They don't like unburned fuel, it lights em off like a furnace.

Best advice for protecting the cats is to keep the secondary ignition stuff (plugs, coils, etc) in good working order

 

OEM Cats and no issues for 215k miles.

 

I had a code for the downstream sensor also at like 160k.
I Pulled it out and cleaned it and put it back in.

I’m a 4banger so only 2 sensors total.
Coded out again 2-3 days later.
I read here that the upstream can cause issues and that to remove the pending code stored to disconnect the battery for at least 20 mins?

I ordered both sensors and while I was waiting to get them I did the battery disconnect for an hr.

Code didn’t return after clearing pending code.
I swapped them both seeing how I had them anyway.
I used Denso also.

I was worried about my cat also again reading here.
My 08 consumes some oil between changes.
I used my bore scope to scope both sides of the cat.
Both ends look pretty white and clean I got photos not sure what I’m looking for but I saw it anyway.

I did find more carbon than I liked on the piston crowns but have used

$25 BG44K BG 44K Fuel System Cleaner Power Enhancer 11oz.

BG44K and it’s removed a lot of it.
I got pics of this also.

I recently installed a oil catch can and wish I’d done it a lot sooner.

Short story made long have you disconnected the battery long enough for it to forget?

 

Thank you all for the responses, very helpful. Learning a lot. To be clear I did not do any of the sensor work myself. I was gungho on it but could not get the sensor loose in the middle of winter. One mechanic after the other has failed to make it right.

I assume the system was reset. Each time I got the truck back the cel light was off and like say, 7 miles later, on again.

I do burn premium gas almost exclusively as it makes the truck run a lot better. Probly ready for a tuneup. Runnin kinda rough.

Bringing it to the dealer Monday, I will report back.

 

So, I think the problem is fixed (knock knock). The code was p0138. The tech “tested voltages and found the air/fuel sensor and the oxygen sensors switching inconsistently.” They were both replaced. Cel is off and stays off. Truck runs and smells much better. The parts were expensive. Air/fuel $212, oxygen sensor $186. Genuine toyota parts. The truck was there for two days while they ordered the parts. They charged very little for labor. I think it was a goodwill gesture. I hope this is the end of it.

 

Glad to here you got it sorted out

 

Thanks man. The guess work I first heard was maybe something wrong with the wiring to the sensor, but that didn’t sound quite right to me.