I hear ya man, its definitely frustrating! Why don't you take off the faulty sensor you bought and return it? I just listed two for sale if you end up needing some, they came off my stock headers. Even if the sensor you installed is used, I'm sure the store you bought them from will take the sensor back if its acting up. Then it saves the trouble of finding the short. Not sure if the wiring extension melting or crimping could be a cause though, maybe someone else can chime in on it. As for the other code, I did a search on the forum here and found some threads with that code, I think a few people found a fix in the is350 platform.

 

What inner diameter is required for the Thermo-Flex to fit?

 

We use the 5/8"

 

P0138 - O2 Oxygen Sensor Circuit High Voltage (Bank1, Sensor2)

This code is saying that the computer is seeing too much voltage on the O2 sensor in the midpipe on the driver's side. It usually means there is a short circuit which can be diagnosed the same way as described on the other code.

But, because you have the other code on the same side for the A/F sensor, I would fix that code first and see if the P0138 comes back. It could be caused by the other code. The computer compares the voltage from the rear O2 sensor to the voltage from the front A/F sensor. Since the front sensor has a short/no voltage, this could cause the computer to set the P0138.

 

only time I got codes with my ppe headers on was when I had to fill up at an arco gas station next to my house. Maybe try changing gas station?? Never went there again and all was fine