COMMAND LINE PRESSURE
"DESIRED"
PRESSURE GAUGE READINGS
"ACTUAL"
Figure 16
DIAGNOSTIC INFORMATION:
VISUAL/PHYSICAL UNDERHOOD INSPECTION
A careful visual and physical underhood inspection must
be performed as part of any diagnostic procedure or in
finding the cause of a failure. This can often lead to fixing a
problem without further steps. Inspect wiring, fluid, cables
and linkage. Inspect all the wires in the engine
compartment for proper connections, burned or chafed
spots, pinched wires, or contact with sharp edges or hot
exhaust manifolds. This visual/physical inspection is very
important. It must be done carefully and thoroughly.
DIAGNOSTIC TROUBLE CODES
Diagnostic trouble codes or information flags are two digit
numbers that can range from 11 to 99. When a malfunction
(MALF) is detected by the PCM, a diagnostic trouble code
or information flag is set and the
malfunction indicator lamp (MIL) telltale lamp may be
illuminated.
Diagnostic Trouble Code (DTC): Suspected failure
detected in the engine or transaxle will turn on MIL lamp
when failure is present.
Information flag: A diagnostic aid used when a minor
malfunction or intermittent problem occurs. It does not
necessarily indicate a failure.
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MALFUNCTION INDICATOR LAMP
This telltale lamp (SERVICE ENGINE SOON telltale
lamp) is in the instrument cluster and has the following
functions:
It informs the driver that a problem has occurred and that
the vehicle should be taken for service as soon as
reasonably possible.
It displays diagnostic trouble codes and/or information
flags stored by the PCM which help the technician
diagnose system problems.
It indicates "Open Loop" or "Closed Loop" engine
operation.
As a bulb and system check, the lamp will come on with
the key On and the engine not running. When the engine is
started, the lamp will turn off. If the lamp remains on, the
self-diagnostic system has detected a problem. If the
problem goes away, the lamp will go out in most cases
after 10 seconds, but a diagnostic trouble code will remain
stored in the PCM.
When the lamp remains on while the engine is running, or
when a malfunction is suspected due to a driveability
problem, code retrieval must be performed. All engine
codes, diagnosis and repairs should be dealt with first
before attempting to move onto the transaxle codes and
information flags.
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11
AUTOMATIC TRANSMISSION SERVICE GROUP
Technical Service Information