The vehicle is a 5AT 2006 TL with about 125k KM. I have been getting these specific codes for a while now: P0138, P0139, P0158, P0159, which indicate something is wrong with the oxygen sensors. I go out and replace every single sensor, and everything seemed good but I am still getting these codes within about a day or two. Sometimes they will go away on their own, sometimes I clear them myself. I thought I had fixed it because I lowered the tire pressure to 230 front/220 back one day and after I did this, the problem did not show up for almost two weeks.

Other strange codes that I might get rarely are: P0113, P0118, P0406, P0717, and P0718. These will only show up if the VSA lights comes on with the CEL, which usually causes the temperature gauge to either go max hot or max cold, and is fixed with a restart (VSA/temp gauge back to normal, CEL still on).

I have spent hours trying to search for the cause of this problem (some threads on here have this exact same problem but the solution is never told/OP never responds again) - so I was wondering if anyone has ever experienced the same problem and knows a probable fix.

 

Anyone have any idea? I'll take anything by this point

 

if you changed ALL 4 O2 sensors and they are still reading bad, then you can conclude that the cat is on its way out, leading to those bad 02 readings.

 

Woah...I wouldn't kill the sleeping dog yet because you thought he was dying...want an easy, inexpensive way of taking your car's heartbeat? Get an OBDII Bluetooth adapter, get Torque Pro on Android. Run the tests on the app, add some logging plugins and get a good baseline in the different fuel mixtures, air/fuel ratios, air volume going in, Co2 coming out of the exhaust and compare to OEM specs. If your car is on its way out, you will see readings ALL OVER THE PLACE. Of course, you can have one or two, possibly 3 sensors acting up, but Torques connects to more than 50 sensors all around the car.

 

What are some symptoms of a failing cat? And wouldn't I have gotten a CEL code for it also?
Just ordered an adapter from Amazon. I'll see how this goes.

 

my bad, i misread cat for car. Even though, I think bad cat symptoms are more performance related than anything. Declining performance, increase in fuel consumption, weird smell out of exhaust...

Also, if your front o2 sensor has given you a code, chances are it's not the cat.

 

So I did some tests and with the cel on and off I am getting an air fuel ratio of 14.7:1 and the secondary o2 sensor voltage fluctuations between 0.0 and 1.0, when idling and driving. So does that mean they are working properly?