[onyourheadtop]

Hello everyone.

I understood that MHD clears the engine code for running a catless set up, which I liked because ofc I don't want to see an engine light on my dash, but if a different engine code were to throw a fault, is that supposed to show up on the dash?

For example, I haven't had a single engine light appear after tuning MHD, but I run the code reader through MHD occasionally and once and a while there would have been a code, one for a misfire and another for my fan.

I'm concerned because I would want to be notified if an engine code would throw a fault other than being catless, but not constantly have to check with a code reader just to see that.

Thanks for any help

2014 435i xDrive
MHD Stage 2+
catless, fmic, dp, cp

[Skyhigh]

When selecting an aftermarket Downpipe, MHD disables the health check of the cat. That's all it does or should be doing. It does not prevent other CELs to be displayed, this would be very wrong, as you point out as well.

The reason you find some historical codes stored is that not every fault is a CEL. There are thousands of possible fault codes, only a subset however are classified as CEL- triggers.