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Section 2: Diagnosing with the Tester
2-1 Preliminary Checks
Before using the OBD II System Tester on your vehicle, it is a good idea to perform a
complete visual inspection. You can find the cause of many driveability problems by
just looking, thereby saving yourself a lot of time. Check the following items before
proceeding with OBD II System Tester testing:
o Has the vehicle been serviced recently? Sometimes things get reconnected in
the wrong place, or not at all.
o Dont take shortcuts. Inspect hoses and wiring which may be difficult to see
because of location beneath air cleaner housings, alternators and similar
components.
o Inspect the air cleaner and ductwork for defects.
o Check sensors and actuators for damage.
o Inspect all vacuum hoses for:
Correct routing. Refer to vehicle service manual, or Vehicle Emission Control
Information (VECI) decal located in the engine compartment.
Pinches and kinks.
Splits, cuts or breaks.
o Inspect wiring for:
Contact with sharp edges (this happens frequently).
Contact with hot surfaces, such as exhaust manifolds.
Pinched, burned or chafed insulation.
Proper routing and connections.
o Check electrical connectors for:
Corrosion on pins.
Bent or damaged pins.
Contacts not properly seated in housing.
Bad wire crimps to terminals.
NOTE: Problems with connectors are common in the engine control system. Inspect
them carefully for corrosion, bent pins, pushed out pins, or over expanded
pins. Some connectors use a special grease on the contacts to prevent
corrosion. Do not wipe off! Obtain extra grease, if needed, from your vehicle
dealer. It is a special type for this purpose.
2-2 OBD II Functions
During the functions described below, a communication link is established, allowing
the OBD II System Tester and the vehicles PCM to exchange information. The way in
which this information is exchanged is referred to as a data stream or data links. The
OBD II Function Menu shows all OBD II Generic functions. Not every vehicle will have
every function that is listed. If the function or part of function selected is not supported
by the vehicle, a message screen informing you of this will be displayed.