Repeating O2 sensor codes :(

Hello all! I bought a 2008 taco used and now need to get it smogged. The check engine light for bank 1 sensor 2 and bank 2 sensor 2 keeps coming back on! I had my toyota mechanic replace both sensors with OEM and even got a new purge valve. Even after verifying voltage and heating, the light comes on AGAIN for same codes. He said i have to take it to dealer for either a faulty computer or the catalytic converter. Has this ever happened to anyone before?

 

The purge valve is unrelated to the exhaust emissions, can you share which specific codes are triggering?

 

P0138 is one (bank 1 sensor 2) and the same code for bank 2 sensor 2 (dont have the specific code right now, sorry) will have them tomorrow. Before the purge valve was replaced these were all the codes, down to just the o2 sensor codes now

 

Do a proper diagnosis before you start replacing parts.

 

I had one mechanic look at it who replaced the (charcoal canister?) and the O2 sensors. This was to prevent a hefty dealer charge for minor repairs. It was worth a shot.

It's at a different toyota shop now, they have done a proper diagnostics and said the dealer has to take a look now because the o2 code came BACK on. Thanks for that tip, by the way.

 

P0138 and p0157 are the codes that keep poping up.

 

So Toyota's have a thing about high voltage to the downstream O2 sensors, often it's caused by erroneous readings from the upstream A/F sensors.

It's more of an issue with the 3.5 2GR's but it can happen on any engine.

That said, one code is high voltage (which we usually suspect the A/F) and one code is opposite bank low voltage (we suspect the o2 sensor itself)

The sensors are faulting because they are working, just not in the perimeters set by the ECU. Also if the cat was failing you would have P0420 and P0430 associated to your o2 codes. If they were plugged you'd have a misfire and lack of power.

I would need a freeze frame for any further advise, I'd need to know voltages of all the sensors and the fuel trim on each bank.

You're gonna need them to look at it.

 

^This is an excellent "pre-diagnosis"--the man knows his stuff...

 

Yes sir excellent indeed, thank you. So here is the info from "the toy shop"

B1S2 - 0.80v (changing slowly)
B2S2 - 0.08v (changing rapidly)

Long term fuel trim numbers were in the 17-20% range. Fixed an air leak at the air mass meter which reduced the fuel trim by 3%.

 

The dealer replaced both A/F sensors. Its been 100 miles and no check engine light.

 

Where are the af sensors located at?

 

Ex manifolds

 

How much did they run? I thought those were the o2 sensors? I have the URD o2 simulator, but im still throwing the same codes. Im in the middle of replacing my charcoal filter and adding a "2003 + 4-Runner " fuel neck to extend my gas line for my fiberglasd bedsides. I believe I have a fuel/ air leak .

 

https://www.toyotapartsdeal.com/oem...ta&Model=Tacoma&Year=2006&Submodel=&Filter=()

 

Tor splains a little here

https://www.tacomaworld.com/threads/narrowband-wideband-air-fuel.313430/

 

This was an excellent comment, thank you. The dealer has determined that my A/F sensors were throwing out weird readings, so they replaced them... after 150 more miles, the O2 sensor codes came back on again! Any other suggestions? The dealer is saying I might need another ECU.

 

I'm having the same codes, even after replacing both downstream o2 sensors. The 2 relays under the hood were fine. This check engine light is driving me mad.

Anyone know how to fix this problem?

 

So, after i replaced both downstream sensors the first time, the same codes came on (read above in the thread for code #). Then i replaced both A/F sensors. THEN once the ECU was finally getting the right readings, the 0420 code came on for one of my catalytic converters. Had to chase it all the way down to the cat. Good luck. My truck has 137k miles on it so i guess it's just that time...

 

Wait but why isn't the cat code showing up then after I replaced both sensors? My truck has 108,000 miles.

Isnt the A/F sensor the same thing as the downstream sensors?

 

Try replacing your intake manifold or header studs with new and use lock washers or lock nuts. You need "external torx" sockets to do so however the parts are cheap.

I replaced my header gaskets at the same time because the gap caused by the header nuts working loose destroyed the existing gaskets.

Runs like a champ now AND no more CEL's ...