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.
1990 Geo Metro L3-61 1.0LFACTORY OEM SERVICE PROCEDURE
Engine Control Module: Description and Operation
The ECM is a precision unit consisting of a one chip microcomputer, A/D (Analog/Digital) converter, I/O (Input/Output) unit, ROM (Read Only Memory) and RAM (Random Access Memory). It is an essential part of the electronic control system, its functions include major functions, as to control the fuel injector, ISC solenoid valve, fuel pump relay, etc.
The ECM diagnoses troubles which may occur in the system when the ignition switch is "ON" and the engine is running. It indicates the result by turning on or flashing the "CHECK ENGINE" light when a fault occurs in any of the following systems:
^ Oxygen Sensor.
^ Coolant Temperature Sensor.
^ Throttle Switch (M/T model) or Throttle Position Sensor (A/T model).
^ Manifold Air Temperature Sensor.
^ Pressure Sensor.
^ Ignition Signal.
^ Crank Angle Sensor.
^ Vehicle Speed Sensor.
^ EGR system.
^ CPU (Central Processing Unit) of the ECM.
The ECM diagnoses troubles which may occur in the system when the ignition switch is "ON" and the engine is running. It indicates the result by turning on or flashing the "CHECK ENGINE" light when a fault occurs in any of the following systems:
^ Oxygen Sensor.
^ Coolant Temperature Sensor.
^ Throttle Switch (M/T model) or Throttle Position Sensor (A/T model).
^ Manifold Air Temperature Sensor.
^ Pressure Sensor.
^ Ignition Signal.
^ Crank Angle Sensor.
^ Vehicle Speed Sensor.
^ EGR system.
^ CPU (Central Processing Unit) of the ECM.
Factory Service Tools
Use the Manual With the Right Hardware
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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.