O2 Sensor?

2007 Liberty threw a code today, P0138 - O2 Sensor 1/2 Circuit High

So that tells me Bank 1, 2nd (Downstream) O2 sensor has finally bit the dust?
And if so, I know I need the NTK replacement - https://www.rockauto.com/en/moreinfo.php?pk=1644772&cc=1433762&pt=5132&jsn=270

This seem correct? Any input would be appreciated if not!

MarksmanAkula said:

2007 Liberty threw a code today, P0138 - O2 Sensor 1/2 Circuit High

So that tells me Bank 1, 2nd (Downstream) O2 sensor has finally bit the dust?
And if so, I know I need the NTK replacement - https://www.rockauto.com/en/moreinfo.php?pk=1644772&cc=1433762&pt=5132&jsn=270

This seem correct? Any input would be appreciated if not!

Click to expand...

Do you have a scan tool that will show data? If so you can watch the data for the rear O2 and see what the voltages are reading - it should not fluctuate but be steady around .5 volts or so.

derekj said:

Do you have a scan tool that will show data? If so you can watch the data for the rear O2 and see what the voltages are reading - it should not fluctuate but be steady around .5 volts or so.

Click to expand...

I do have a tool that can do LD. Is the .5 Volts at idle right after engine start?

MarksmanAkula said:

I do have a tool that can do LD. Is the .5 Volts at idle right after engine start?

Click to expand...

After driving it for a bit - it will take the sensor a minute to warm up to get a proper reading. It is best to check it while driving as sometimes they can give a false reading when the vehicle is idling.

You can swap right and left rear sensors, clear codes and see if the high volt code moves, too. If it does, you know it's the sensor.

Unless you have inspection concerns or want to ensure the cat is doing its job on that side, you could just ignore it, also, as that sensor is mostly just for emissions reporting.

I have this issue sometimes with my Jeep(2003 Libby Renegade), which I am pretty sure has a squanched wire to the heater of Bank 1 Sensor 2 when the engine was replaced. I almost always have a pending fault code of P0141, which is because it heats up slower than the other three, which I can see with my OBDII dongle and Torque Pro. I have replaced both Bank 1's with NGKs and the issue still persisted.


At start up, you have a nominal voltage of 1v across all sensors, at least according to my ODBII dongle and Torque pro. As they warm up, they drop below 1v. However, at least for me, if I do something like idle with no stress on the engine, the exhaust temps drop enough to cause the sensor to gain voltage to above 1v, which triggers the high voltage code. This also happens if I hit a large puddle and don't stress the engine or go through the car wash and the under body clean cools the sensor and I don't press the accelerator b/c I'm in neutral.