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Introduction to On-Board Diagnostics OBD II
On-board diagnostics version II (OBD II) is a system that the Society of
Automotive Engineers (SAE) developed to standardize automotive
electronic diagnosis.
Beginning in 1996, most new vehicles sold in the United States were
fully OBD II compliant.
Technicians can now use the same tool to test any OBD II
compliant vehicle without special adapters. SAE established
guidelines that provide:
A universal connector, called the DLC, with dedicated pin
assignments.
A standard location for the DLC, visible under the dash on
driver’s side.
A standard list of diagnostic trouble codes (DTCs) used by
all manufacturers.
A standard list of parameter identification (PID) data used
by all manufacturers.
Ability for vehicle systems to record operating conditions
when a fault occurs.
Expanded diagnostic capabilities that records a code
whenever a condition occurs that affects vehicle emissions.
Ability to clear stored codes from the vehicle’s memory with
a Scan Tool.
SAE Publications
SAE has published hundreds of pages of text defining a standard
communication protocol that establishes hardware, software, and
circuit parameters of OBD II systems.
• SAE publishes recommendations, not laws, but the Environmental
Protection Agency (EPA) and California Air Resources Board
(CARB) made many of SAE’s recommendations legal requirements.