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On-Board Diagnostics II (OBDII)

July 18th, 2010 · No Comments

injection systems and a catalytic converter, and one of the most effective pollutant reduction
combinations is the 3-way catalytic converter combined with a lambda (excess-air factor or air
ratio) closed-loop control system.
In order to achieve the precise control that these modern systems require, virtually all of the
automobiles and light trucks manufactured in North America since the early 1980s are equipped
with an on-board computer. The vehicle’s computer controls engine parameters such as the fuel
injection system performance under dynamic operating conditions. These ’smart’ computer
systems are also known as On-Board Diagnostics or OBD systems.
The first OBD systems were manufacturer specific. That is the systems conformed to each
vehicle manufacturer’s design, hardware and software requirements. As such in order for a repair
technician to interrogate the On-Board Diagnostics, the technician had to have access to the
connection hardware and computer codes for each specific make and model vehicle. Also, while
computerized OBD systems have been used to monitor vehicle systems since the 1980s, most of
the earlier OBD systems monitored few if any emission control parameters.
More recently, the OBD systems on LDVs have been standardized and expanded to include the
monitoring of most emissions control systems. These modern OBD systems, labelled OBD II,
are now subject to regulation in the USA and Canada.
Standardization was the key. In general, OBD II systems, regardless of the type of vehicle, now
monitor the same components, use the same computer language, and have the same criteria for
evaluating systems and indicating problems to the driver and the repair technician.
The OBD II system monitors emission control systems and key engine components. When a
problem that could cause a substantial increase in air emissions is detected, the OBD system
turns on a dashboard warning light, the emissions Malfunction Indicator Light or MIL, to alert the
driver of the need to have the vehicle checked by a repair technician. The OBD system monitors
the status of up to 11 emission control related subsystems by performing either continuous or
periodic tests of specific components and vehicle conditions.


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