Description of On-Board Diagnostics

ECU BACK-UP FUNCTIONS
1. Fail-Safe Function
When an abnormality occurs in a signal from a sensor, the ECU ignores that signal and assumes a pre-programmed value that allows the engine to continue to run.

2. Back-up Function
When an abnormality occurs in the ECU itself, the injectors are controlled by a back-up circuit independent of the system in order to permit minimal driving.

3. Self-diagnosis Function (Check Engine warning light, LEO indicator)
When an abnormality occurs in a signal from a sensor, the ECU lights the Check Engine warning light, stores the failure code in erasable memory and indicates the code with the LEO on the ECU anytime the ignition is on. When the ignition is initially turned on, the ECU supplies ground for the Check Engine warning light for two seconds.