John252058

My 2018 Q5 2.0 lt TFSI started derating the engine, no DTC's, temp gauge normal or any notable drivability issues. What activates the engine speed 4000 rpm derate notification? After some research I've read the engine coolant temperature control actuator can cause the issue, using my VCDS I checked engine temp (90*C) and activated the actuator (some what noisy). Any suggestions would be appreciated!

SMac770

It's very unlikely you are DTC free if you are being capped to 4k rpm. That limit usually kicks in when there's an issue with the EPC (throttle by wire system, accelerator pedal, etc) or oil pressure (you will have a dash message) or such. If the ECM knows it needs to limit rpm, it knows why it's doing so. Are you checking fault codes while the engine is still running with the message active? Besides checking fault codes-02 under 01-engine, also check under 02-auto trans and 03-abs/esp. You could log the oil pressure switch status and see if it's toggling open for high pressure. If the engine can't confirm the oil pump high pressure mode is working when in high pressure mode, it will restrain the rpm limit:

Activation of oil pressure switch valve
Status of oil pressure switches-Oil pressure switch for high pressure
Status of oil pressure switches-Oil pressure switch for low pressure

John252058

Thanks for the info SMac770, this is very helpful. I'll check the other ECM's for codes while the message is up. Do you know a source to Audi SSP's free or pay for use.

SMac770

I just google search for Audi SSP xxx and see what comes up. procarmanuals.com is where I could read most of them.