Heavy Duty & OBDII Diagnostic Tool HD V3.0
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SAE J1939 can be considered the replacement for the older SAE J1708
and SAE J1587 specifications.
SAE J1939 has been adopted widely by diesel engine manufacturers.
One driving force behind this is the increasing adoption of the engine
Electronic Control Unit (ECU), which provides one method of controlling
exhaust gas emissions within US and European standards. Consequently,
SAE J1939 can now be found in a range of diesel-powered applications:
vehicles (on – and off - road), marine propulsion, power generation and
industrial pumping.
Applications of J1939 now include off-highway, truck, bus, and even
some passenger car applications.
2.4 OBD Definitions
Powertrain Control Module (PCM) -- OBD II terminology for the
on-board computer that controls engine and drive train.
Malfunction Indicator Light (MIL) -- Malfunction Indicator Light
(Service Engine Soon, Check Engine) is a term used for the light on the
instrument panel. It is to alert the driver and / or the repair technician that
there is a problem with one or more of vehicle‟s systems and may cause
emissions to exceed federal standards. If the MIL illuminates with a steady
light, it indicates that a problem has been detected and the vehicle should be
serviced as soon as possible. Under certain conditions, the dashboard light
will blink or flash. This indicates a severe problem and flashing is intended to
discourage vehicle operation. The vehicle onboard diagnostic system cannot
turn the MIL off until the necessary repairs are completed or the condition no
longer exists. DTC-Diagnostic Trouble Codes (DTC) that identifies which
section of the emission control system has malfunctioned.
Enabling Criteria -- Also termed Enabling Conditions. They are the
vehicle – specific events or conditions that must occur within the engine
before the various monitors will set, or run. Some monitors require the vehicle
to follow a prescribed " drive cycle " routine as part of the enabling criteria.
Drive cycles vary among vehicles and for each monitor in any particular
vehicle. Please refer to the vehicle‟s factory service manual for specific
enabling procedures.
OBD II Drive Cycle -- A specific mode of vehicle operation that provides
conditions required to set all the readiness monitors applicable to the vehicle
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