toyota training course t874 engine control systems II ch03

Section 3

Engine Control Module (ECM)

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Basic ECM The engine’s electronic control system includes:
Operation
•Sensors that detect various engine conditions
•ECM
•Actuators that control the operation of system components
Sensors (Inputs)

Sensors convert engine operating conditions (such as temperature, RPM,
throttle position, and other factors) into electrical signals which the ECM
constantly monitors.

ECM

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.

Actuators (Outputs)

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.

Toyota Engine Control Systems I

Course 852

17


Introduction to ECM

Engine Control Module (ECM)

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Introduction to ECM 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.
Overview of
ECM-Controlled Systems

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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Engine Control Module (ECM)

Power Distribution and Ground Circuits

Slide 22
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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.
Power Distribution
•Battery power is constant and powers the ECM as long as the
battery is connected.
ECM Power and
Ground Circuits

•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.
ECM Memory

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 nonvolatile memory and remains even when the battery is disconnected.

Toyota Engine Control Systems I

Course 852

19


Power Distribution and Ground Circuits, cont.

ECM Ground Circuits

Engine Control Module (ECM)

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.

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Engine Control Module (ECM)

Voltage Control Signal

Slide 23
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Voltage Control The ECM sends out a regulated voltage of 5 volts on the voltage control
Signal (VC or VCC) signal line. This voltage is used by many sensors including
pressure and position sensors.
VC Short

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.

Toyota Engine Control Systems I

Course 852

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Engine Control Module (ECM)

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