Prizm L4-1800cc 1.8L DOHC (1993)
Malfunction Indicator Lamp: Description and Operation
This lamp is on the instrument panel and has the following functions:
^
It informs the driver that a problem has occurred and that the vehicle should be taken for service as soon as reasonably possible.
^
It displays "Trouble Codes" stored by the PCM which help the technician diagnose system problems, when the diagnostic terminal is grounded
with a spare fuse in the fuse box.
As a bulb and system check, the lamp will come "ON" with the key "ON" and the engine not running. When the engine is started, the lamp will turn
"OFF." If the lamp remains "ON," the self-diagnostic system has detected a problem. If the problem goes away, the lamp will go out in most cases after
10 seconds, but a Trouble Code will remain stored in the PCM. When the lamp remains "ON" while the engine is running, or when a malfunction is
suspected due to a driveability or emissions problem, the ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK must be performed.
The PCM and Malfunction Indicator Lamp (MIL) operates as follows:
The Malfunction Indicator Lamp (MIL) illuminates when the ignition switch is turned "ON" (but the engine is stopped) with the diagnostic request
terminals ungrounded regardless of the condition of EFI system. This is only to check the Malfunction Indicator Lamp (MIL) bulb and its circuit. If the
EFI system is free from any faults after the engine starts (while engine is running), the Malfunction Indicator Lamp (MIL) turns "OFF." If any trouble
exists, it may turn "OFF" but only until the PCM detects that fault. When PCM detects a trouble which has occurred in the above areas, it turns the
Malfunction Indicator Lamp (MIL) "ON" while the engine is running to warn the driver of the occurrence of a fault and at the same time it stores the
trouble code in PCM memory. (The code is kept in memory even if the fault was only temporary and disappeared immediately. It is not erased unless the
power to PCM is shut off for 10 seconds or longer.) The PCM also indicates trouble codes in memory by means of flashing of Malfunction Indicator
Lamp (MIL) at the time of inspection (i.e. when the diagnostic request terminals is grounded and ignition switch is turned "ON").
Even when trouble has occurred in the EFI system and a fault is detected by the PCM, control over the injectors, IAC valve and others is maintained on
the basis of the standard signals and/or back-up program prestored in the PCM. This function is called "fail-safe function." Thus, with this function, a
certain level of engine performance is available even when some failure occurs and disability in running is avoided. The systems covered are as follows:
^
Oxygen Sensor (O2S)
^
Engine Coolant Temperature (ECT) Sensor.
^
Intake Air Temperature (IAT) Sensor.
^
Manifold Absolute Pressure (MAP) Sensor.
^
Vehicle Speed Sensor (VSS).
^
Knock Sensor (KS).
^
Exhaust Gas Recirculation (EGR) system.
^
CPU in the PCM.
