1.6.8.1 Monitoring Function
The injection deactivation is a diagnosis to protect the catalysts from overheating. More specifically, this is an additional fuel pressure diagnosis which requires a very short diagnostic time and which reacts early by deactivating some injectors. Additionally, the fuel tank level is evaluated. When the tank level is low, the DTC changes to provide better information for the repair shop.
The diagnosis first evaluates the air-fuel deviation by analyzing both the short term fuel trim and the difference between the measured air fuel ratio and the set-point air fuel ratio. Both analyses only detect the lean side of the mixture. When a lean deviation occurs, the diagnosis either compares the difference between the measured pressure, the set-point of the high pressure, and the absolute value of the high pressure sensor with a threshold, or it monitors the absolute value of the low pressure sensor. A DTC is then set and a certain amount of injectors are shut off. This reaction prevents the catalysts from overheating. The fuel tank level (≈ 0 liters) affects which DTC is then stored.