System Operation

MPI SYSTEM INSPECTION
(1) Before removing or installing a part, read diagnosis code and then disconnect the battery (-) terminal cable.
(2) Before disconnecting the cable from battery terminal, turn the ignition switch to OFF. Removal or connection of battery cable during engine operation or while the ignition switch is ON could cause erroneous operation to the engine control unit or damage to semiconductors.
(3) The control harnesses between the engine control unit and oxygen sensor are shielded wires with shield grounded to the body in order to prevent influence of ignition noises and radio interference. When the shielded wire is faulty, the control harness must be replaced.

SELF-DIAGNOSIS
The engine control unit monitors the input/output signals (some signals at all times and the others under specified conditions) to the engine control unit.
When it is noticed that an irregularity has continued for a specified time or longer from when the irregular signal is initially monitored, passing a certain number, the engine control unit judges that an irregularity has occurred, memorizes the malfunction code, and outputs the signal to the self- diagnosis output terminal.
There are 14 diagnosis items, including the normal state, and the diagnosis results can be read out with a voltmeter or multi-use tester.
Moreover, since memorization of the malfunction codes is backed up directly by the battery, the diagnosis results are memorized even if the ignition key is turned off. The malfunction codes will, however, be erased when the battery terminal or the engine control unit connector is disconnected.

CAUTION: If the sensor connector is disconnected with the ignition switch turned on, the malfunction code is memorized. In this case, disconnect the battery terminal (-) for 10 seconds or more, and the diagnosis memory will be erased.







DIAGNOSTIC CHART
The 14 diagnosis items are provided in the table, and if plural items are activated, they are all indicated sequentially from the smallest code number.