I own a 2014 Mercedes’ Benz c350 sport I recently changed 5 of the spark plugs 1 I couldn’t get and the intake plenum gaskets were also changed about a week maybe two the check engine light came on and this error code P0040 showed up is it possible what I changed caused it? And if so how would I go about fixing it.

 

What did your research tell you causes P0040?

 

The P0040 code is set when the powertrain control module or PCM perceives that the wiring harnesses from the sensors have been crossed. It determines this through a logic-based strategy. Code P0040 refers to a condition wherein the first oxygen (O2) sensors downstream from the engine have swapped wiring.
This is what I found about the code so since it’s down stream it could be what I changed? Thanks for the help.

 

And if you search on this website you will find more info about how to try to resolve this. The consensus was what you found and to try swapping connections and/or use new ORIGINAL O2 sensors.

 

Yes I was just asking if what I changed the spark plugs and plenum gaskets could cause the P0040 error code to appear from a bad spark plug or the gaskets not sealing properly.


I think what you meant was what I changed could of caused it and if so thanks for all your help

 

Changing the plugs is a pain in the *** since you have to remove the intake manifold and disconnect several wires. It is possible that you either missed a connection when you put things back together. Plugs or the seals should not cause this code, but I could be wrong. However, all of the fixes mention connecting the O2 sensors correctly or replacing them with new OE sensors.

 

I was worried that I messed something up when I changed them and it was what caused the issues.
Thanks so much for all your help.

 

The other possibility is the crank position sensor may be bad. But I think if that was the case, both banks of cylinders would throw codes.