The P0285 code on your 2019 Mercedes-Benz GLE indicates a performance issue with the fuel additive dosing valve. This code relates to diesel exhaust fluid (DEF) or similar additive injection systems used for emissions control.
Understanding the System
Modern diesel vehicles use Selective Catalytic Reduction (SCR) to reduce NOx emissions. The system injects DEF (AdBlue in Mercedes terminology) into the exhaust stream. The dosing valve controls this injection. P0285 indicates this valve isn't performing within expected parameters.
GLE Engine Context
The 2019 GLE offers both gasoline and diesel options. In the US, the GLE 350d and GLE 400d (diesel) would have this system. Gasoline GLEs wouldn't use DEF injection, making this code unexpected on gas models. Verify your engine type first.
Diesel Model Diagnosis
For diesel GLEs, the dosing valve (also called DEF injector) is located in the exhaust system ahead of the SCR catalyst. Issues include clogged injector nozzle from crystallized DEF, electrical failures in the injector, or control issues from the ECU. DEF quality also affects system performance.
Repair Approach
Crystallized DEF can sometimes be cleaned. Faulty dosing valves require replacement. Ensure you're using quality DEF—contaminated fluid causes system problems. Mercedes dealers have specific diagnostic procedures for AdBlue systems. After repair, the system may need reset through XENTRY diagnostics.