Last year after replacing a valve on the head, i got a p0420 code and got a used manifold off ebay. Installed it, went away till recently.

No problem, it was used with whoknows how many miles on it. A stopgap fix.

Recently, 30k later, i got codes for b1s1 sensor. Replaced it, and it stayed away for a while. Then it came back with P0420!

Ok, i ordered a manifold off of rockauto. Installed it, glad i did, the oil filter housing was leaking like a sieve, fixed that too.

The old after cat sensor was siezed in. So i had to install that too. To sum up, new cat, new upstream and down stream sensors.

Stayed off for a few drive cycles, and its back. p0420.

When i watch graphing with torque, b1s2 is acting normal, but b1s1 isnt available, only "alternate" is. Im guessing its the computer guessing whats happening from the b1s2 info and using a prewritten fuel map.

Whats my next step, does that mean the DME isnt seeing the O2 sensor (precat)? Bad sensor, bad wiring? It runs smooth and perfect, very quiet.

Any advice would help. Anyone else experience this?

 

Been 2 months, anyone?