# How to test O2 sensors



## J-Man (Nov 13, 2001)

Is there a guide how to test O2 sensors or their connections back to the computer? I recently replaced all of them and one of them is giving me a P1110 code consistently. Off the top of my head it's something like short to B+ or similar. I turned the key on/engine off and tested pins 1 to 4 on both B2S2 as well as B1S2 and they were identical readings from the plugs coming from the computer. I would have expected if I had a real short I would have seen different readings?? Oh and neither were 12v, it was like 3.5...weird. Is there a way I can get to the ECU side of the cable and do a resistance test? Where would it be located?

Anyway, any suggestions how to trace down where the issue is is most appreciated.

Thanks.


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## J-Man (Nov 13, 2001)

I pulled the ECU and tested resistance from the connection to both the green and brown O2 sensor plugs. No shorts.
I then ran across the following article which suggests a different in resistance from the new plug (13552 <same one i purchased) and the original. I kept the original and verified that resistance is about 8 ohms whereas the new one is indeed 3. Could this really be the cause? I'm down for replacing it again, just want to be sure this is an accurate fix.

https://answers.yahoo.com/question/index?qid=20110820121232AAKi6P1


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## Wayne Kerr (Jun 25, 2016)

There are a few things you can do to check the sensor, but top of my list would be to check the heater circuit fuse.
After that, you could swap the two rear sensors. If the code follows the sensor, (P1105) then it's your culprit. If not, then it's the wiring.
I once had an O2 sensor heating circuit issue, and found the following link to be very useful:
https://www.motor.com/magazine-summary/diagnosing-o2-sensor-heater-circuit-failures/


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## a1ccook (Nov 2, 2015)

Wayne Kerr said:


> There are a few things you can do to check the sensor, but top of my list would be to check the heater circuit fuse.
> After that, you could swap the two rear sensors. If the code follows the sensor, (P1105) then it's your culprit. If not, then it's the wiring.
> I once had an O2 sensor heating circuit issue, and found the following link to be very useful:
> https://www.motor.com/magazine-summary/diagnosing-o2-sensor-heater-circuit-failures/


I'm getting these errors (amongst others):

16519	P0135	O2 Sensor Heater Circ.,Bank1-Sensor1 Malfunction
16539	P0155	O2 Sensor Heater Circ.,Bank2-Sensor1 Malfunction

Going to read that link and see if it helps!


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## J-Man (Nov 13, 2001)

Wayne Kerr said:


> There are a few things you can do to check the sensor, but top of my list would be to check the heater circuit fuse.
> After that, you could swap the two rear sensors. If the code follows the sensor, (P1105) then it's your culprit. If not, then it's the wiring.
> I once had an O2 sensor heating circuit issue, and found the following link to be very useful:
> https://www.motor.com/magazine-summary/diagnosing-o2-sensor-heater-circuit-failures/


Thanks. Unfortunately due to "German engineering" this particular O2 sensor has a connector type that's different from all other 3 sensors and they won't cross plug...go figure. I did put my original one back in and did not immediately have the error as I was seeing. I will have to drive it more to see after I get it put back together. Thanks for the info.


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## Wayne Kerr (Jun 25, 2016)

Those are the front sensors now. I'd say you either have a bad ground, or possibly your voltage regulator is fubar and burning out the heater elements.


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