Engine Control Module: Description and Operation

ECU Location:

The ECU (located behind the dash bolster to the left of the driver) consists of an 8-bit microprocessor, random access memory (RAM), read only memory (ROM) and Input/output (I/0) interface. Based on the information from the input sensors, the ECU determines the optimum control for the operating conditions and drives the output actuators accordingly. The ECU actively controls the operation of the Fuel Injection system, the Ignition timing, and has full control of the Idle Speed Control system. Additionally the ECU interrupts the operation of the Air Conditioning and EGR systems under some conditions, and controls the power to the Fuel Pump. In addition to this the engine control unit monitors the input/output signals of the engine control unit (some signals at all times and others under specific conditions). When it is noticed that an irregularity has continued for a specified time, the engine control unit judges that an irregularity has occurred, memorizes the trouble code, and outputs the signal to the self-diagnosis output terminal. There are 15 diagnosis items (including the normal state). The diagnosis results can be read out with a voltmeter or multi-use tester. Moreover, since memorization of the trouble codes is backed up directly by the battery, the diagnosis results are held in memory even if the ignition key is turned off. The trouble codes will, however, be erased when the battery terminal or the engine control unit connector is disconnected.

CAUTION:
1. When battery voltage is low, trouble codes can not be read. Be sure to check the battery for voltage and other conditions before starting the test.
2. Diagnosis memory is erased if the battery or the ECU connector is disconnected. Do not disconnect the battery before the trouble codes are completely read.
3. After checks and repairs are completed, disconnect the ground cable for 15 seconds or more from the negative terminal of the battery to erase any trouble codes.
4. If a sensor connector is disconnected with the ignition switch turned on, a diagnosis code will be memorized. In this case, disconnect the battery negative terminal for 15 seconds or more, and the diagnosis memory will be erased.