In Selective Catalytic Reduction (SCR) systems, the catalyst (TWC) is used to convert nitrogen oxides into dinitrogen and water. To achieve this, a gaseous reductant is used, which is added to the exhaust stream and adsorbed by the TWC. The reductant that is injected into the exhaust is known as Diesel Exhaust Fluid (DEF), with which a higher temperature of the Diesel Particulate Filter (DPF) is achieved, thus obtaining a higher performance of the same.
The pump that supplies the reducer is used to pressurize the fluid in the system when needed. The voltage of this pump is constantly monitored by the Powertrain Control Module (PCM) to check the constant fluctuation of the fluid and the load percentage. For this, the PCM monitors one or more pressure sensors in the system to check for leaks.
When the diagnostic code P2040 OBD2 is stored, it means that a high input was detected in the “A” circuit of the Injection Air Pressure Sensor. However, this code is used by some manufacturers, at their discretion. For example on Mercedes vehicles, this code is used to indicate that the Oil Quality Sensor has a high or out-of-range signal.