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2
The original on-board diagnostics (OBD I) lacked consistency in communica-
tion and interface while allowing different interpretations amongst vehicle man-
ufacturers. 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 nec-
essary). Details on adapter cables and jumper wires may be found in “Diag-
nostic Link Connectors (DLC)” on page 2-3.
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 used in 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 Con-
troller
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.
Chrysler On-Board Diagnostics
System Long Name Years Description
SMEC
Single Module Engine
Controller
1989–1990
Used a 6-pin Serial Communication Interface (SCI) DLC
and has bidirectional capability.
SBEC
Single Board Engine
Controller
1989*–1995
Used two types of DLCs: a 6-pin SCI and a 6-pin LH
series.
The first to allow a tool to reset the EMR light on trucks.
OBD II
PCM
OBD II Powertrain
Control Module
1995**– present
Complies with OBD II regulations and uses the OBD II
J1962 DLC.
JTEC
Jeep/Truck Engine
Controller
1996– present
Complies with OBD II regulations and uses the OBD II
J1962 DLC.
The JTEC system is used on light-duty trucks and Jeeps
* In 1989, the SBEC system was installed in selected vehicles with 3.0L V6 engines.
** Some vehicles in 1995 were equipped with the OBD II PCM.