Description of On-Board Diagnostics

Electronic Control System

The functions of the fuel and emission control systems are managed by the engine control module (ECM) on vehicles with manual transmissions or the powertrain control module (PCM) on vehicles with automatic transmissions.

Fail-safe Function
When an abnormality occurs in the signal from a sensor, the ECM/PCM ignores that signal and assumes a pre-programmed value for the sensor that allows the engine to continue to run.

Back-up Function
When an abnormality occurs in the ECM/PCM, the injectors are controlled by a back up circuit independent of the system to permit minimal driving.

Self-diagnosis
When an abnormality occurs in the signal from a sensor, the ECM/PCM supplies ground for the malfunction indicator lamp (MIL) and stores the diagnostic trouble code (DTC) in erasable memory. When the ignition is first turned on, the ECM/PCM supplies ground to the MIL for 15 to 20 seconds to check the MIL bulb condition. If all readiness code are not set, the MIL will flash five times. If readiness codes are set to complete, the MIL will go out

Two Driving Cycle Detection Method
To prevent false indications, the "two driving cycle detection method" is used for some self diagnostic functions. When an abnormality occurs, the ECM/PCM stores it in its memory. When the same abnormality recurs after the ignition switch is turned OFF and ON (II) again, the ECM/PCM turns on the MIL.

Self Shut Down Mode (SSD)
After the ignition switch is turned off, the ECM/PCM stays ON (up to 15 minutes)

If the ECM/PCM connector is disconnected during this mode, the ECM/PCM may be damaged. To cancel this mode, disconnect the negative cable from the battery or jump the SCS line with the HDS after the key is turned off.