Fuel and Emissions System Description - Electrical Control System

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.

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 in erasable memory (RAM). Depending on the failure, a DTC is stored in either the 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 for the failure in the RAM 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 for the failure in RAM. The MIL does not come on at this time. If the failure continues in the second drive cycle, the ECM/PCM stores a DTC in erasable memory 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 substitute a pre-programmed value, for them that allows the engine to continue running. This causes a DTC to be stored and the MIL to come on.

MIL Bulb Check

When the ignition switch is 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). 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.