The Engine Control Unit or ECU is a designated computer that was developed to
manage the engine control system. The ECU consists of electronics which are mounted
on multi-layer circuit board. The ECM monitors and adjusts the air/fuel mixture
and utilizes a catalytic converter to minimize amount of pollution produced from
the engine. There are two modes of operation, closed loop, which means the computer
has completely taking over the operation system. And open loop which is used when
the engine is cold and operates on a preset program. The engine must be at operating
temperature before it can go into closed loop.
The ECM monitors the input and output signals produced by various sensors in
the system. The ECM then adjusts the system as necessary. Sensors can include:
oxygen sensor, coolant sensor,
mass air flow sensor, air intake sensor, crankshaft angle sensor, throttle position
sensor, camshaft angle sensor and knock sensor. The ECM operating program consists
of information cells. These cells hold the code for proper engine operation, if
information is out side the cell parameters a MIL (malfunction inductor lamp) or
"check engine light".
Once a "check
engine" or a "service
engine soon" light in your instrument cluster has illuminated the ECM has stored
a
diagnostic trouble code. This means the computer system on your vehicle has
detected a problem with the various systems it controls. Your car or truck has many
different sensors that monitor the various vehicle systems. If the trouble code
light has been illuminated your vehicle enters into "limp mode" this means it is
running on a predetermined program that causes poor mileage and increased emissions.
An engine trouble code reader is an easy to use tool. All 1996 and newer vehicles
utilize a "D" style plug-in connector that connects to the code reader. On most
vehicles the connector is located at the driver's compartment. Once the code reader
is plugged in you can retrieve trouble codes the engine computer has stored in its
memory. These codes are the same codes the dealer and repair shops use to replace
sensors and clear codes.
The ECM outputs a 5 volt reference to most sensors to drive the monitoring circuits.
The ECM also controls the radiator cooling fan, air pump controls,
fuel pump,
EVAP system and more depending on the vehicle. Communication
standards have being established in the OBD2 operating system. Among the communication
standards controller area networking or CAN has become very popular and can achieve
communication speeds of more than 500 Kbps, which is faster than most communication
standards.
Advantages of using buses for communication is that if a fault occurs with any of
the process modules, it can be reported separately to a diagnostic tool. Manufacturers
have different
trouble code faults although some are generic. Wiring is simplified by a technique
known as multiplexing. In this kind of wiring system is assigned for each module,
which consolidates the output and input for that module.
How Does it Work
/ Car
Computer ECM
Check Manufacturer Specific Car Computer
Questions and Answers
Related Subjects
Got a Car Repair Question
we will answer it for FREE!
GET AN
ONLINE REPAIR MANUAL
FOR YOUR CAR. Get instant access to your vehicles drive belt routing, wiring
diagrams, trouble code information and other available updates and factory bulletins.
