2009 toyota tacoma oxygen sensor diagnostic codes

i have a 2009 tacoma with 4 litre engine . the truck has 375 000 km on it and just did the clutch 25 000 km ago for a bit of history.

2 days ago i had my check engine light come on and i quickly scanned the codes and was getting

p2195 oxygen sensor signal biased /stuck lean bank 1 sensor 1
and
p0138 oxygen sensor circuit high voltage bank1 sensor 2

i erased the codes to see if they came back up as ive had codes light up dues to moisture ect

today the check engine light came back on this time i was only getting p0138 the sensor circuit high voltage code

i scrolled through the scanner and my coolant temp was 187 degrees

and these are the following voltage readings i was getting

o2s12 - .740 volts
o2s22 - .2 to .8 volts
o2s11 - 3.4 volts
o2s21 - 3.3 volts

i briefly looked up p0138 codes online and it seems that a failed o2 sensor seems the most likley however did notice that one article said it could occur with a blown head gasket. i change my oil every 5000 km and have never seen any signs of coolant in the oil. the radiator and overflow tank look clean as a whistle and i had the coolant changed a year or so ago.

any insight into the codes would be appreciated. ive never changed o2 sensors before im assuming they arent that difficult? how hard of a job is it to do an head gasket ?

 

At 233k miles o2 sensors could be considered basic maintenance.

They should be easy unless you are in salt country and everything is rusted up.

Lots of other testing to be done before even thinking about headgadket work. Not something to dive into unless confirmed failure.

 

I'd suspect the Bank 1 (passenger side) upstream AFR sensor is failing/biased lean so the PCM is adding more fuel than it should resulting in the downstream O2 sensor reporting rich.
How is your fuel trims, are they within about +/-10% total and 5% bank to bank?

 

High voltage code could also be the wiring to the O2. Inspect that and the connector itself to be sure it is seated.

 

i ordered both afr sensors and both oxygen sensors from a local toyota dealer as they were within 100 dollars of aftermarket ones at most shops. 1200 for all of them.
the code p0138 keeps coming up and i checked the obd scanner for the fuel trims and here is what i got

at idle speed


ST ftrm1 -1.6 to + .8
LT ftrm1 20.3
ST ftrm2 -.8 to + 1.6
ST ftrm2 10.2

i am not overly sure what these mean so if someone could help that would be great

i am going to try and change the sensors tommorrow and want to start with the ones causing the code fault and if i have time the other ones as well.

since both sensors in question are in bank 1 is that passenger or driver side?

hopefully the sensors come out ok. im going to wire brush the bungs and heat them up and apply some bees wax to hopefully make the job easier

thanks

 

Definitely adding fuel on both banks (+20% on bank 1 and +10% on bank 2) and bank to bank is 10% difference, sure looks like it could be a biased sensor.

Bank 1 is Passenger side.

 

well i got sensor 1 and 2 on the passenger side freed up and changes as well as the down stream one on the driver side. they were seized in tight but i used a blow torch and some candle wax to soak the threads and they popped . new sensors are installed and torqued to 33 ftlb. unfortunatley the driver side upstream sensor on the exhaust manifold is being a pain in the neck. i heated it up and put some wax into the threads but it didnt want to budge . ive left some penetrating oil soaking overnight and will try again tommorrow.

 

after letting the sensor soak and then using a good amount of heat and wax the sensor came loose. i will be taking it for a test drive this evening. while under the truck i changed the engine oil as well as gear oil in diffs,t-case and trans.

 

Can you share what the "wax" is you're using to help free up the sensor, I've not heard of that (or that name) before.

 

It’s an old timers trick. Candle wax gets melted into seized threads & acts like a penetrating oil.

 

i just used birthday cake candles which would be paraffin . im sure beeswax would work as well. you just heat the area around the threads with a blow torch and alot like soldering you just feed the candle to the threads and capillary action draws the wax in. it works great.

 

well i just finished cleaning up all my tools the evening and getting the wheels torqued and i plugged the scanner in to clear any existing codes prior to start up . this time there where 3 codes showing the first initial ones i listed p2195 and p0138 and p0171 system too lean bank 1. im very much hoping that the sensors have just failed outright and thats why this code has come up and its not a secondary issues. i guess ill find out after work tommorrow.

 

well ive been driving my truck for the last 3 days and seems to be idling well and no check engine light has come back on. knock on wood

 

i have noticed that on start up there seems to be a ticking noise on the drivers side area of the engine. ill have to see if there is an exaust leak in that area. ( this was not on the sensor bank in question that i repaired but i did change when with new sensors while i was at it. the joys of high mileage vehicles