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Getting Started
2
INTRODUCTION TO ON-BOARD DIAGNOSTICS
The original on-board diagnostics (OBD I) lacked consistency in
communication and interface while allowing different interpretations amongst
vehicle manufacturers. Ford and Chrysler used different types of engine control
computers and data link connectors, and GM varied the trouble codes and
communication protocols from year-to-year.
The tables below highlight changes for GM, Ford, and Chrysler. If this seems
confusing; don’t worry. Your tool makes it easy. Based on the VIN information
selected during Scan Tool setup, the processor is automatically recognized. All
you have to do is choose the correct adapter cable and jumper wires (if
necessary). Details on adapter cables and jumper wires may be found in
“Diagnostic Link Connectors (DLC)” on page2-5
.
GM On-Board Diagnostics
System Years Description
OBD I Control Module
1981–1995
Most vehicles used the 12-pin ALDL (Assembly Line Data Link)
located under the dash on the driver side. Some 94-95 vehicles
used the 16-pin OBD II (J1962) data link connector (DLC), but
use the Historical application software. Refer to the vehicle’s
Vehicle Emission Control Information label.
OBD II Control Module
1994*-Present Complies with OBD II regulations and uses the J1962 DLC.

*

OBD II system is used on certain 1994-1995 vehicles equipped with a 2.2L, 2.3L, 3.8L, 4.3L or 5.7L
engines.
Ford On-Board Diagnostics
System Long Name Years Description
MCU
Microprocessor Control Unit 1980 –1991 Used in police vehicles, containing carbureted
engines. Uses the MCU DLC.
EEC-IV
Electronic Engine Control,
Fourth generation 1984 –1995 Most Ford vehicles equipped with North
American engines. Uses the EEC-IV DLC.
MECS
Mazda Electronic Control
System 1988 –1995 Vehicles equipped with Mazda-sourced engines.
Uses MECS 6-pin and 17-pin DLCs.
EEC-V
Electronic Engine Control,
Fifth generation 1994* – present Complies with OBD II regulations and uses the
OBD II J1962 DLC.
PTEC
Powertrain Electronic
Controller 2000 – present Complies with OBD II regulations and uses the
OBD II J1962 DLC.
* EEC-V OBD II system used in 1994-1995 vehicles equipped with a 3.8L or 4.6L engine.