My 80,000 mile 09 ES350 has a random reoccurring P0138 code. I have checked all the wiring & voltages. I replaced the bank 1 sensor 2 along with 6 new coil packs (Genuine Lexus) and new plugs. I have what appears to be a minor skip under load on the highway (sometimes worse than others) but no codes for that. I'm leaning toward a dirty/bad injector but like I said there are no codes other than the P0138. Are the aftermarket new injectors any good? I have heard that the reconditioned DENSO injectors are not always a good choice. Anyone have any suggestions?

 

You've probably have a leaky injector, or an issue with the 02 sensor wiring harness

one user replaced the upstream sensor:

https://www.clublexus.com/forums/is-...h-voltage.html

Another changed the a/f ratio sensor:

https://www.clublexus.com/forums/es-...en-sensor.html

 

In almost every case of that code, the pre-cat O2 is the culprit.

 

Thank you very much for your reply. I see others have also replaced the A/F sensor to fix that code so I just ordered a new one. I'll post back once I install it and see if it solves my issue. Is it common for the A/F sensor to fail and not throw a code?

 

in this case they don’t fail, but they give false information

 

I installed the new A/F sensor today and took it for a nice long ride on the highway and around town, No CEL anymore. Thanks to all that helped on this.