Failure detection system of exhaust secondary air supply system of

Abstract

A failure detection system detects a failure occurring in an exhaust secondary air supply system of an internal combustion engine, and has a catalytic converter installed in an exhaust pipe of an exhaust system of the engine for reducing pollutants from exhaust gases emitted from the engine, a conduit connected, at one end, to the exhaust pipe at a location upstream of the catalytic converter and an air pump connected to an opposite end of the conduit for supplying compressed air in the conduit. The conduit is closed by the a valve which opens in response to the negative pressure and a second valve which opens in response to the conduit pressure. In the system a first prescribed level and the second prescribed level are set and two pressure switches are provided for generating output at the levels. A failure occurring in the air pump and the valve is detected based on operation of the air pump and the output of the pressure detectors. Alternatively, the failure is detected by changing the timing of the termination of the air pump and closing of the second valve while using one switch and the second prescribed level. The system is simple in configuration.