Mercury MerCruiser D2.8L D-Tronic Service Manual page 580

EDI DIAGNOSIS
SCAN CODE TOOL
IMPORTANT: If a scan tool is used to read the codes, follow the manufacturer's
instructions.
The ECM can communicate a variety of information through the DLC connector. This data
is transmitted at a high frequency which requires a scan tool for interpretation.
With an understanding of the data which the tool displays, and knowledge of the circuits
involved, the tool can be very useful in obtaining information which would be more difficult
or impossible to obtain with other equipment.
Scan tools Do NOT make the use of diagnostic charts unnecessary, nor can they indicate
exactly where a problem is in a particular circuit.
The scan tool allows manipulation of wiring harnesses or components with the engine not
operating, while observing the scan tool readout.
The scan tool can be plugged in and observed while operating the vessel under the
condition when the Malfunction Indicator Lamp illuminates 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 operating 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 senor's readings with those of the EDI / Scan Tool Normal
Specifications 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 is the technician's ability to
understand the system 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.
Page 5E-12
SERVICE MANUAL NUMBER 22
90-860074--1 FEBRUARY 2002