SO recently my exhaust clamps rusted through and ripped my cat in 2, so Having replaced the clamps and purchasing a cat from O'reilly auto for 300$ because I didn't want to buy a 1100$ one from Audi. I'm getting a bank 1, Sensor 1, catalyst efficiency below threshold...how can a 4 week old cat be that dirty? possible one of the sensors is just bad?

Any solutions short of buying an 1100$ cat?

 

what yr/motor do you have... i have a cat in my garage before you buy a dealer one


and yes it could be a bad sensor

 

It's a 1998.5 1.8t, if it were a bad sensor would it be bank 1 or 2?

 

Bank 1 Sensor 1 is the drivers side exhaust manifold sensor (if thats the side that has cylinder 1 in it, it is on my 2.8L 12V engine) , if its throwing a cat low efficiency code (OBD2 Code P420) it should be coming from a post cat O2 Sensor 2 which will either be Bank 1 sensor 2, or Bank 2 Sensor 2.

 

U only have one bank it's an inline 4 cyl and it's more than likely ur after cat o2 it's the one that determines cat efficency

 

So try pulling the back 2 sensor? sounds like fun :/ to think I already had the damn thing ripped apart

 

If it says sensor 1, it's the pre-cat sensor. There's no reason it'd be saying it's cat efficiency. If it's cat efficiency it's sensor 2. If it's sensor 1, you should see it as a fuel trim code or a malfunction of the heater circuit in the sensor. Cat efficiency and sensor 1 are mutually exclusive. Doublecheck your code and definition.

 

Ok this is ridiculous, it has thrown two codes now, and they have to be related somehow. the first one was P0420 telling me the catalyst efficiency was below threshold and then there was P1136, which is apparently telling me my engine is running too lean?

 

Sounds like a bad primary O2 sensor to me. If it is reading too lean then:

a) Your computer will think your car is running lean (and will make it run too rich to try and compensate)

b) Your computer will be comparing a too-lean initial value to the post-cat value, and think the cat isn't dropping that initial value enough... but really the initial value is just wrong.

 

For $300 you could've had a high flow cat from 034 or Labree.