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Q: Engine light code PO141. Replaced O2 sensor (Bank 1 Sensor 2), light came back. on 1996 Toyota Corolla

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Engine light code PO141. Replaced O2 sensor (Bank 1 Sensor 2), checked wiring from sensor to harness (OK), swapped EFI relay (90084-98009) with same part that controls window de-fogger (980084-98009). Engine light stays off until car reaches normal operating temp and continues to stay off while driving. But, after turning off the engine and restarting it, the light comes back on.
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Did you use a factory quality sensor? Very important, or you may have received a defective/poor quality part. Where did you purchase the Oxygen sensor? Check the new part, the heater element is the 2 wires that are the same color and should ohm check at about 2 ohms. Ohm check your old sensor for reference. Also make sure that your connector is making good contact and make sure that you have a good ground(s). How strong is your battery? Sounds crazy, but the oxygen sensor heater circuit needs a strong battery, I have fixed many problems with this. when you crank over the car, the computer looks at the cranking voltage, and if it is weak, it will not trust the heater circuit.
So these are a couple of things to keep in mind. Did you verify that the B1S2 heater circuit is getting a 12 volt signal when you are driving the car?
I used a Bosch 12108 as a replacement. When it didn't solve the problem, I exchanged it for another one at Autozone. The battery is new, but I'll test it. All wiring, fuses & relays have been checked. I don't know about the B1S2 heater circuit. I'll do some research on that. While researching OB-II Codes for PO141, one reference said it could be the catalytic convertor sensor. However, that is bank 1 sensor 3 and the read out I get is definitley bank 1 sensor 2. Thanx
did you replace the correct sensor? B1S2 is the sensor AFTER the catalytic converter. also, I advise you use factory (toyota) parts.
Yes, I replaced the one directly upstream from the sensor on the converter. Also, gas mileage does not seem to be effected by this condition. It still gets 35-37 mpg.
there are only two sensors on this car, one on the exhaust manifold(b1S1) & one after the catalytic converter(B1S2). B1S2 is down stream of the cat (between the cat & muffler). this sensor should have 4 wires. the sensor on the exhaust manifold (B1S1) has two wires.
There are four oxygen sensors, not two. Heated Oxygen Sensor Bank 1 Sensor 1, Bank 2 Sensor 1, Bank 1 Sensor 2, Catalyst Monitor Bank 1 Sensor 3. The error code says B1S2.
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