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O2 Sensor

I have 2002 Toyota Rav4 with 105,000 miles. It?s an automatic with all wheel drive. There are 4 different O2 sensors in the car and one of them is bad. When scanning the car I get an error code P1155. I got an estimate of $350 to fix it. How long can I drive the car before replacing the O2 sensor? How hard is it to do yourself and how do I tell which O2 sensor needs to be replace? Any help would be appreciated. Thank you!!

How are you determining that an O? is bad?

The code indicates that the heater circuit for O2 sensor bank 1 sensor 2 is defective. This O2 sensor would be located on the same side of the engine as cylinder #1, and the O2 sensor after the catalytic converter.

This O2 sensor monitors the catalytic converter efficiency only, so it doesn’t effect engine performance. So there’s no real rush to replace it.

To replace the O2 sensor, an O2 sensor socket is used. This inexpensive tool can be purchased at any auto parts store. So with the tool and a new O2 sensor, you could replace the sensor for less than a hundred bucks.


first thing you do is go under the car. find the correct O2 sensor. find the connector plug and then figure out how to UN connect it. clean the connections, and make sure there is no grime in the connections, clean them with electrical contact cleaner, then re clip them. clear the code and see this has fixed the O2 sensor error.

if this doesn’t work, then yes, you do need to replace the sensor. if you are a little bit mechanically inclined, and VERY strong you should be able to replace the sensor yourself. BUT a word of warning, the sensor is installed in the exhaust pipe. these get repeatedly heated up and corroded. they can be a BEAR to remove.

I determining that the O2 sensor is bad from the error code.

I may be wrong here so please correct me if i am Tester. I thought that when the CEL light is on it puts the ECM in a closed loop mode where the engine runs off of preset perimeters stored in the ECM. If this is the case then it could cause problems. When all sensors are working properly the ECM goes into an open loop mode which allows the engine to run off the sensors on the engine. I may have the open and closed loop backwards. Questioning this to see if this is correct or not. Thanks and Tester your still the most knowledgeable person on this subjuct.

The computer is in the open loop mode when the engine is cold. When in this mode the computer controls the fuel from the signals it recieves from the coolant temp sensor, the throttle position sensor, MAF sensor, and the crank position sensor. Once the engine reaches operating temperature the computer goes into the closed loop mode. When in this mode fuel control is based on the signals the computer recieves from the O2 sensor(s).


The error code is A/F Sensor Heater Circuit Malfunction. It is more likely to be a wiring or PCM problem than one of the 02 sensors. No OBDII code absolutely says that a particular part is bad, the codes only indicate what the PCM is seeing. It gives you a starting point to start testing to find the actual problem.