How do you check O2 sensors?

[Luis]

Lately, my 4.0L 96 Explorer is giving me troubles. It has 81k miles. Check Engine Light came on about a month ago. I bought OBDII scanner and the code shows P0141. Checked the internet for instruction on repair but without any luck. Before taking into the dealer, I want to try to fix it myself. Although I'm not sure if the sensors itself is at fault. The repair manual states the cause as being 'grounded'. Anyways, I went under the car and saw 3 O2 sensors. 2 before and 1 after converter. Do I really need to buy all 3 sensors? Can't I replace only the bad one? Question: How do I check if the sensors are okay? Repair manual is not much of help. Each sensors have 4 pins (black, gray, 2-white wires). I have volt and ohm meter. Your help is greatly appreciated. Thanks

 

[mrboyle]

The best way to test the O2 sensor is to replace it. There really isn't any way to test one and with 81K they are proabably due for replacement anyway.
Yes you need all 3, each one does a different job and the vehicle requires the info from all three to run properly.

 

[Robert]

Does your OBD-II scanner have the abillity to monitor the voltage on the O2 sensors? If so then you can see which one isn't responding. My Haynes manual also gives a description on how to check the O2 sensors with a VOM.

 

[Luis]

Thanks guys! I got tired of 'trying' to figure out how to check the O2's. I finally figure out what is meant by 'bank 1' & 'sensor 2'. So I went out to Pepboys and bought a new downstream O2. It's fixed now. The light is out! I did not have to replace other two upstream O2...at least for now. Thanks!!

 

[jimmiecakes]

Simple task...... B1S1 = the cylinder bank that is home to cylinder #1 closest sensor to the motor. B2S2 = the none #1 cylinder bank, furthest sensor from the motor.