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 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 either first or the 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 DTC and turns on the MIL.

- 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 at this time. 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, stores a DTC and turns on the MIL. The ECM/PCM will use a pre-programmed value for that sensor which allows the engine to continue running. This causes a DTC to be stored and the MIL to comes on.

MIL Bulb Check and Readiness Code Condition

When the ignition switch is turned ON (II), the ECM/PCM supplies ground to the MIL circuit for about 15 to 20 seconds to check the bulb condition. If any readiness codes are not set to complete, the MIL flashes five times. If all readiness codes are set to complete, the MIL goes out.

Self Shut Down (SSD) Mode

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 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 the ignition switch is turned OFF.