Electronic Control System
The functions of the fuel and emission control systems are managed by the engine control module (ECM) on vehicles with manual transmission, or the powertrain control module (PCM) on vehicles with automatic transmissions.
Self-diagnosis
The ECM/PCM detects a failure of a signal from a sensor or from another control unit and stores a Temporary DTC or a DTC. Depending on the failure, a DTC is stored in the first or second drive cycle. When a DTC is stored, the ECM/PCM turns on the malfunction indicator lamp (MIL) by supplying ground to the MIL circuit.

- One Drive Cycle Detection Method
  When an abnormality occurs in the signal from a sensor or from another control unit, the ECM/PCM stores a Temporary DTC and a DTC at the same time for the failure and turns on the MIL immediately.

- Two Drive Cycle Detection Method
  When an abnormality occurs in the signal from a sensor or from another control unit in the first drive cycle, the ECM/PCM stores a Temporary DTC. The MIL does not come on. If the failure continues in the second drive cycle, the ECM/PCM stores a DTC and turns on the MIL.

Fail-safe Function
When an abnormality occurs in the signal from a sensor or from another control unit, the ECM/PCM ignores that signal and assumes a pre-programmed value that allows the engine to continue running. A DTC is stored, and the MIL comes on.
MIL Bulb Check
When the ignition switch is first turned ON (II), the ECM/PCM supplies ground to the MIL circuit for 2 seconds to check the bulb condition.
Self Shut Down (SSD) Mode
After the ignition switch is turned OFF, the ECM/PCM stays on (up to 15 minutes) to monitor the vehicle. If the ECM/PCM connector is disconnected during this time, 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 turning the ignition switch OFF.