Another code yesterday P 0138. The car has a recent aftermarket Cat. And it was bitterly cold so I'm not sure if that has something to do with it, but figured I might as well replace it. Does anyone have any brand recommendations?
I'll probably just reset the codes and see how long it takes to come back. I was reading that the aftermarket cats can make it throw codes periodically, and the O2 sensors are bit pricey to replace without being sure.
If you DO end up buying the first sensor, the consensus here is to get the OEM Denso one, which is a wide-band type. This would be important at cold start-ups. Are you experiencing any rough running, especially when cold?
The secondary (monitor) sensor is physically located in the MIDDLE of the 'cat, so it or its connector COULD have been damaged (or, is not reading correctly) because the converter design is different.
If you are certain that the engine is running OK, you could try one of these extenders:
I decided I will take it back to the shop that replaced the CAT. I could replace both )2 sensors but I'm concerned that maybe the CAT went bad and figured they could test it. It should have some kind of warranty.
The shop tested and diagnosed the rear 02 sensor as being bad, with 100% certainty. They replaced the sensor and unfortunately the code is back with another. Originally I had the P0138 only, now I have P0138 and P0139, so I need to take it back in. Both codes still seem to point to the rear sensor but I am wondering if the forward sensor needs replaced or if I might have a leaking injector.
The car is used by my daughter and we really like this car, but I am very much regretting purchasing it. It' is like I keep paying for the same repairs over and over and never actually get them fixed.
You called it. They said they used after market and it was not signaling fast enough. They said they replaced it with a NTK, they just charged me the difference for the higher priced NTK. Hopefully it is good now.