1.6.5.1 Monitoring Function
The injection deactivation diagnosis protects the catalysts from overheating. More precisely, this diagnosis is an additional fuel pressure monitor which requires a very short diagnostic time period and which reacts early by deactivating some injectors. Additionally, the fuel tank level is evaluated in the diagnosis. When the tank level is low, the DTC changes to provide better information for the auto repair shop.
The diagnosis first evaluates the A/F deviation by analyzing both the short-term fuel trim and the difference between the measured AFR and the set-point AFR. 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 value, the high pressure set-point value, and the high pressure sensor absolute value with a threshold, or the diagnosis monitors the low pressure sensor absolute value. A DTC is then set and a certain number of injectors are shut off. This reaction prevents the catalysts from overheating. The fuel tank level (≈ 0 liters) affects which DTC is then stored.