My check engine light came on, went to the local parts store and they put an obd2 scanner on it and said my Bank 1 Sensor 1 was defective and needed to be replaced. I replaced the O2 sensor that was located before the Cat two times now. First sensor was a Bosch and the second Volvo OE. Check engine light never went away. Once in a great while it would go off but then would come back on. Was told the first sensor must have been defective so I replaced it again and the results were the same. I was told that the code needs to be reset and then drive time afterwards. I aquire a Bluetooth OBD LINK MX and paired it with Torqe ODB2 software. Scaned for codes and found two. P0135 - Powertrain, O2 Sensor Heater Circuit (Bank 1 Sensor 1). P2251 - Powertrain, O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1. I have reset the codes but they eventually come back.

I am wondering if I am resetting the codes properly? I reset the codes with the ignition turned to position II. Then went for a two hour drive. The check engine light came on after turning the engine off for an hour then starting it - check engine light comes on shortly after starting.

If I have reset the code properly then what would be my next troubleshooting steps?

 

Just because a code says there is a problem with a specific sensor, it doesn't mean that that sensor is bad. Ive seen a bad rear oxygen sensor cause the light to come on but the code was for the front O2 sensor. That doesn't mean that is the problem but you need to have it properly diagnosed.

 

Thanks damien360.

I am assuming many people on this forum , like myself, prefer to do the work themselves and would like to avoid paying for the dealer proprietary knowledge.

On the recommendation of the part store I replaced the sensor and then replaced the sensor a second time as the part store stated the first sensor must have been defective.

I purchased a OBD2 code reader to assist in troubleshooting the check engine light further. The P0135 code does point to the sensor but the odds of this sensor being defective is slim to none. However, the P2251 code does point to an area that could be causing the P0135 code.

I was hoping someone on this forum had experienced this and would be willing to share what they found and did to fix the issue. Or offer tips on how to troubleshoot the P2251 - Powertrain, O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1.

I would appreciate input on the next steps on how to troubleshoot these codes.

Thanks everyone.

 

I would suspect that there is something wrong with the O2 sensor circuit, not the sensor itself. The way I'm reading the P2251 code, it says that there is an open in the circuit which means that there could be a broken wire or bad connection somewhere. I could be completely wrong though, but that's where I would start.

 

Can anyone offer tips on how to troubleshoot the P2251 - Powertrain, O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1? Or where I can find a good service manual for 2005 S60 2.5th AWD?