Looking for Toyota Echo B1S2 help
 

Basically the CEL came on the other day. I checked the code and it was P0141 which points to the Bank 1 Sensor 2 Heated Oxygen Sensor. Reset the CEL so it was off just to make sure it wasn't a false alarm and it came back on within 1/2 hour of driving. So I unplugged it and checked the resistance of terminals HT and +B, which came up open. Thought I would see if the CEL would come back on with the sensor unplugged and it never did.

Can anyone tell me how the system works? What causes the CEL to come on if the circuit is open anyway with the sensor plugged in?

Or should I just replace the sensor and not bother trying to figure it out? I'd hate to waste my money buying something that isn't needed and the problem is somewhere else.

The system uses 2-trip detection to check current in the O2, and will trip the CEL if current is greater than 2A or less than 0.2A. This is lifted straight from the Toyota FSM.

I would fancy trying to replace the O2 first. B1S2 is the sensor further away.

Thanks for the reply CorneringArtist.

So the system uses the B1S2 sensor to check that the O2 sensor in front of the converter is doing it's job and if isn't, it will turn on the CEL? That would make sense to replace the first O2 sensor since it isn't working properly.

What do you think of the aftermarket sensors? Or would the OEM sensors be the better way to go?

There are two separate codes for each O2 sensor, P0134 is for B1S1, while your code is specifically for B1S2.

Aftermarket sensor should be fine, but if you want the comfort in OEM parts, by all means go for it.

usually the second o2 is used to make sure the cat is working

Oem is the way to go but if you go aftermarket go with NTK brand. Stay far far away from Bosch o2 sensors.

I've heard that the Bosch ones are problematic. I dropped by NAPA and was going to buy both sensors and be done with the problem until I found that they are around $125 each before taxes. It's not like I have money to throw around............. Doing more searching on the internet, I've found many other people have had the same code and ended up replacing the rear B1S2 sensor which did the job.