P0138 Code help!

Welcome to PriusChat!!

How are you reading the OBD2 codes?

How many miles do you currently have on this vehicle?

Here is the workup for DTC P0138:

https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8CPDF%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/2054m/cip0136.pdf

 

Did you replaced the right oxygen sensor?
There several things that can cause the problem.
1. Check to be sure that its the sensor underneath the car you need to replace (that's sensor two!).
2. If you did that, and it still didn't work, check the wiring harnesse from the ECU straight to the sensor concerned itself.
3. There might an open/short circuit problem on that harness.
If you have rats over there, they may have spliced them.
4. After doing all that and the problem still persists, check for exhaust leaks at the exhaust assembly.
A slight leak, would caused this code, and you'd have a rich condition(excess fuel consumption).
5. Make sure there aren't intake air leaks also at the manifold, or throttle assembly.

Hope this helps.

PS: clear the codes first with a scantool, or have the battery(12v) disconnected for awhile, before reconnecting back to clear the codes.
If it comes back, after some drive cycles, then the problem is still not solved.

 

That DTC is for the REAR O2 sensor and indicates the ECM is getting a signal voltage that is ABOVE expected, so not a rodent problem as they generally cause low voltage codes.

Did you replace the front of rear sensor? This *can* also be due to an overly rich condition, but there are no codes for the FRONT O2 sensor for that condition, so it is very unlikely.