| 摘要 |
PROBLEM TO BE SOLVED: To provide a failure diagnosing system for gas concentration sensor for detecting a failure when a gas concentration sensor provided in a purge line of an engine 1 failed. SOLUTION: In this failure diagnosing system, an ECU 22 measures the converging time from a start of the purge of an oxygen sensor 8 to be changed with the fluctuation of the air-fuel ratio, and compares this converging time with the target converging time Tsp decided on the basis of a load of an engine 1. In the case of the converging time T shorter than the target converging time Tsp, a gas concentration sensor 21 is considered normal, and on the other hand, in the case of the converging time T longer than the target converging time Tsp (=2.0 seconds), the gas concentration sensor 21 is considered failed. Even in the case, therefore, where the gas concentration sensor 21 itself can not determine a failure thereof, the system can diagnose a failure.
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