2009 toyota corolla P0420

Question

I have P0420 in my 2009 corolla. Using my obd2 scanner i get this, B1s1 volt are from 3.1 to 3.3, b1s2 fluctuate from .3 to .6 and b1s1 it fluctuate negative -0.055 to 0 quickly. Can someone help me.

Answer 1

It sounds like your forward O2 sensor (B1S1) is lazy and isn't keeping up with the needs of the engine and therefore needs replaced. The rear 02 sensor (B1S2) only monitors the efficiency of the cat, so doesn't affect how the car is running. It is being a little wild, but that might be because of the forward O2 sensor.

My suggestion is to replace the forward O2 sensor (the one before the catalytic converter) and then let everything settle out. If the forward O2 sensor has been an issue for too long, it may have caused damage to the cat. If replacing the forward O2 sensor doesn't clear the code properly, then you probably need a cat.

Two things:

• When changing the O2 sensor, disconnect the battery while you're doing this. It will reset the ECU. You do this as the ECU needs to learn the new sensor.
• Since you are changing out your forward O2, I'd highly suggest you change out the back one at the same time. O2 sensors are only good for so long.

One last tidbit ... You don't mention how many miles are on the vehicle, nor do you mention if the O2s have ever been changed. The answer above is contingent on that the O2s have never been changed out before. Obviously if the O2s have been changed out 2k miles ago you won't want to change them out again because that'd be a waste of money. If they haven't changed them out and you're over 100k miles, they are past due.