2C3D Code on DocRace 6266 w/ JB4 + Custom BEF


New Member
Nov 20, 2016
Hey guys - Trying to chase down a o2 code gremlin.

Getting the code 2C3D "Lambda probe in front of catalytic converter, control failure".

The O2 sensors and my Single Turbo setup are both 4k miles old and have not presented any issues until now.

- When I clear the code, AFR1 and AFR2 are live and both reading as expected. Eventually the code comes back up and AFR in Bank 1 goes to 20. My thought is that the O2 sensor in Bank 1 is working as expected as the same issue persists when I changed the O2 sensor to a spare one I had.
-The code specifies "Line Fault" or "Control Failure"
-SES Light is on

Attempted Fixes:
-Swapped O2 sensor in Bank 1 with another working O2 sensor, code persists
-Checked JB4 Harness and wiring, looks OK
-Reset Adaptations multiple times via JB4/MHD

-JB4 with custom MHD Backend Flash
-DocRace 6266
-Eldor Coils/ NGK 95706 @ .20

Any help would be appreciated, working on getting logs when it's not wet outside.


Nov 6, 2016
N las vegas NV
Was running OEM Bosch sensors.

This was resolved. Looks like the O2 Sensor was toast even though it was brand new OEM and only 4k miles old. Swapped in another O2 sensor into bank 1 (again) and the code has not returned.
I recommend you get a set of ADV sensors or your going to changing your o2 sensors more then what you like