Scan Tool Use With Intermittents - Mercury MerCruiser MCM 454 Mag MPI Service Manual

MULTI-PORT FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION

Scan Tool Use With Intermittents

The scan tool allows manipulation of wiring harnesses or components with the engine not
running, while observing the scan tool readout.
The scan tool can be plugged in and observed while running the vessel under the condition
when the Malfunction Indicator Lamp turns ON momentarily or when the engine driveability
is momentarily poor. If the problem seems to be related to certain parameters that can be
checked on the scan tool, they should be checked while running the vessel. If there does
not seem to be any correlation between the problem and any specific circuit, the scan tool
can be checked on each position, watching for a period of time to see if there is any change
in the readings that indicates intermittent operation.
The scan tool is also an easy way to compare the operating parameters of a poorly operating
engine with those of a known good one. For example, a sensor may shift in value but not
set a trouble code. Comparing the sensor's readings with those of the typical scan tool data
readings may uncover the problem.
The scan tool has the ability to save time in diagnosis and prevent the replacement of good
parts. The key to using the scan tool successfully for diagnosis lies in the technician's ability
to understand the system he is trying to diagnose as well as an understanding of the scan
tool operation and limitations. The technician should read the tool manufacturer's operating
manual to become familiar with the tool's operation.
CLEARING CODES USING DIAGNOSTIC CODE TOOL (NON-SCAN)
1. Install diagnostic code tool.
2. Turn key ON.
3. Select service mode on code tool.
4. To clear codes, move the throttle, while in neutral, from 0% to 100% then back to 0%.
5. Exit "Service Mode" on code tool.
6. Start engine and let run for fifteen seconds.
7. Turn key OFF for 5 seconds.
8. Select "Service Mode" on code tool.
9. Turn key ON and read codes. If codes are still present, check note following and repeat
from Step 1.
10. Refer to appropriate "Troubleshooting" and/or "Diagnostic Charts."
A poorly charged battery or engine cranking problem may result in an ECM "reset" and may
not allow stored trouble codes to be cleared from EEPROM memory. If this condition exists,
BE SURE the battery is fully charged.
NOTE: If a low battery condition does exists the audio warning buzzer will come on for 2
seconds after engine start-up.
Index
Page 5B-10
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SERVICE MANUAL NUMBER 23
90-861326--1 MARCH 1999