Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSMAZDA1991PROTEGE L4-1839CC 1.8L SOHCREPAIR AND DIAGNOSISPOWERTRAIN MANAGEMENTCOMPUTERS AND CONTROL SYSTEMSRELAYS AND MODULES - COMPUTERS AND CONTROL SYSTEMSENGINE CONTROL MODULEDESCRIPTION AND OPERATION
1991 Mazda Protege L4-1839cc 1.8L SOHC
Engine Control Module: Description and Operation
1991 Mazda Protege L4-1839cc 1.8L SOHCSECTION Description and Operation
NOTE: The ECU constantly monitors input devices for malfunctions. However, it only checks for output device faults during a three second period after the ignition is switched "ON" and diagnosis connector "TEN" terminal is grounded.
The ECU is a computer that judges air/fuel ratio as rich or lean according to a voltage signal generated by an oxygen sensor. Based on oxygen sensor and other input data, the ECU generates a controlling signal to the fuel injectors that regulates "ON" time. Because fuel pressure remains constant, the ECU controls air/fuel ratio adjustments by varying injector "ON" time.
To provide a margin of safety by maintaining driveability in the event of certain system failures, the ECU has a fail-safe mode of preprogrammed values. The output of the ECU will automatically switch to fail-safe mode if a fault is detected in any of these components and/or systems:
^ Airflow meter
^ Atmospheric pressure sensor
^ Feedback system
^ Intake air thermosensor
^ Oxygen sensor
^ Throttle sensor (A/T)
^ Water thermosensor
The ECU incorporates self-diagnostic capability monitored via a dash mounted malfunction indicator lamp (MIL). When the system detects a fault in a monitored component and/or circuit, the lamp will light and stay on (while the engine is running). To extract codes, the technician can either utilize a "Scan" tool or cause the MIL to display codes by grounding the diagnosis connector "TEN" terminal in the engine compartment.
PURPOSE
System functions to facilitate starting if the engine becomes flooded during cold weather.
OPERATION
When specified conditions are met, the ECU prevents injectors from opening during cranking so that spark plugs can dry and excess fuel will be purged from cylinders. Fuel injection is cut when the throttle is held wide open during cranking and coolant temperature is 32°F (0°C) or below.
The ECU is a computer that judges air/fuel ratio as rich or lean according to a voltage signal generated by an oxygen sensor. Based on oxygen sensor and other input data, the ECU generates a controlling signal to the fuel injectors that regulates "ON" time. Because fuel pressure remains constant, the ECU controls air/fuel ratio adjustments by varying injector "ON" time.
To provide a margin of safety by maintaining driveability in the event of certain system failures, the ECU has a fail-safe mode of preprogrammed values. The output of the ECU will automatically switch to fail-safe mode if a fault is detected in any of these components and/or systems:
^ Airflow meter
^ Atmospheric pressure sensor
^ Feedback system
^ Intake air thermosensor
^ Oxygen sensor
^ Throttle sensor (A/T)
^ Water thermosensor
The ECU incorporates self-diagnostic capability monitored via a dash mounted malfunction indicator lamp (MIL). When the system detects a fault in a monitored component and/or circuit, the lamp will light and stay on (while the engine is running). To extract codes, the technician can either utilize a "Scan" tool or cause the MIL to display codes by grounding the diagnosis connector "TEN" terminal in the engine compartment.
Dechoke Control System:
PURPOSE
System functions to facilitate starting if the engine becomes flooded during cold weather.
OPERATION
When specified conditions are met, the ECU prevents injectors from opening during cranking so that spark plugs can dry and excess fuel will be purged from cylinders. Fuel injection is cut when the throttle is held wide open during cranking and coolant temperature is 32°F (0°C) or below.
RENDER: 1.0x
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.