toyota training course t874 engine control systems II ch03

Toyota Engine Control Systems I Course 852 17The engine’s electronic control system includes: • Sensors that detect various engine conditions • ECM • Actuators that control the operation

Toyota Engine Control Systems I Course 852 17

The engine’s electronic control system includes:

• Sensors that detect various engine conditions

• ECM

• Actuators that control the operation of system components Sensors convert engine operating conditions (such as temperature, RPM, throttle position, and other factors) into electrical signals which the ECM constantly monitors

The ECM uses sensor input data and its internal programming to determine what outputs are required to operate engine and emission control systems The ECM may also control other vehicle functions such

as transmission/transaxle control Additional ECM programming performs self-diagnostic checks and stores Diagnostic Trouble Codes (DTCs) if problems are found

The ECM controls the operation of various electrical devices (relays, motors, solenoids, and indicator lights) As actuator operation changes engine operating conditions, sensor data reflects these changes back to the ECM (feedback) and the ECM continually adjusts actuator operation as required

Engine Control Module (ECM)

Section 3

Basic ECM

Operation

Sensors (Inputs)

ECM

Actuators (Outputs)

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The Engine Control Module (ECM) manages a variety of engine systems The fundamentals of engine operation have not changed (correct mixture

of air and fuel sufficiently compressed and ignited at the proper time) Rather, the ECM’s advanced control of these operating factors provides the best possible combination of power output, fuel economy, and low emissions

Each ECM-controlled system can be categorized by its relationship to basic engine operating needs:

• Air induction system

• Fuel system

• Ignition system

• Exhaust/emission control system

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Introduction to ECM Engine Control Module (ECM)

Introduction to ECM

Overview of ECM-Controlled Systems

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Power supply to the ECM allows the ECM and its controlled circuits to operate properly There are two types of power supplied to the ECM: battery power (+B) and switched power

• Battery power is constant and powers the ECM as long as the battery is connected

• Switched power from the EFI (main) relay is only present at the ECM when the ignition switch is ON

Power is also required for the ECM to communicate with an external computer (Techstream) through the diagnostic communication link (DLC3) Current OBD II regulations require a standard DLC

The ECM uses two types of memory: volatile and non-volatile

• Volatile memory is information that is lost when power is disconnected Examples of volatile memory are DTCs and current values for ignition timing, fuel trim, etc The ECM maintains volatile memory with battery power When the battery is disconnected, the ECM may have to “relearn” individual vehicle operating characteristics that were stored in volatile memory

• Non-volatile memory is information that remains even when power

is disconnected Basic ECM programming is an example of non-volatile memory and remains even when the battery is disconnected

ECM Power and

Ground Circuits

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Engine Control Module (ECM) Power Distribution and Ground Circuits

Power Distribution

ECM Memory

The ECM has multiple ground circuits, and it is usually the ground path for sensors and actuators Clean, solid ground connections are

as important as power connections for proper engine control system performance Grounds are usually identified by an “E” followed by a number (e.g E1, E2, etc.)

Multiple ground wires from the ECM are usually attached to the engine with a single stud or bolt DTC sections in the Repair Manual often include a circuit diagram with detailed internal ECM wiring

Power Distribution and Ground Circuits, cont Engine Control Module (ECM)

ECM Ground Circuits

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The ECM sends out a regulated voltage of 5 volts on the voltage control (VC or VCC) signal line This voltage is used by many sensors including pressure and position sensors

A VC short to ground could occur in numerous locations, and it is often mistaken for a bad ECM The most obvious symptom of a VC short to ground is a lack of communication between Techstream and the vehicle ECM/ECUs The MIL may or may not illuminate, and the vehicle may or may not start

Voltage Control

Signal

VC Short

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Engine Control Module (ECM)