Scan Tools; Efi Diagnostic Circuit Check - Mercury MerCruiser MCM 454 Mag MPI Service Manual

SERVICE MANUAL NUMBER 23
SERVICE MODE
When the diagnostic code tool is installed at the Data Link Connector (DLC) and the selector
switch is set at SERVICE, the system will enter what is called the SERVICE mode. In this
mode the ECM will:
1. Display a Code 12 by flashing the Malfunction Indicator Lamp (indicating the system is
2. Display any stored codes by flashing the Malfunction Indicator Lamp. Each code will be
3. The IAC valve moves to its fully extended position, blocking the idle air passage. This
4. Holds ignition advance steady.
NORMAL MODE
Engines can be monitored in the normal mode. Certain parameters can be observed without
changing the engine operating characteristics.

Scan Tools

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. Diagnostic tables incorporate diagnosis
procedures using a scan tool where possible or a Diagnostic Code Tool (non-scan) if a scan
tool is unavailable.

EFI Diagnostic Circuit Check

After the visual/physical inspection, the On Board Diagnostic (OBD) Circuit Check is the
starting point for all diagnostic procedures. Refer to SECTION 5E.
The correct procedure to diagnose a problem is to follow two basic steps.
1. Are the on-board diagnostics working? This is determined by performing the On Board
2. If a code is stored, go directly to the numbered code chart in SECTION 5F or 5G as
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operating correctly).
flashed three times, then Code 12 will be flashed again.
is important to remember, as an attempt to run the vessel while in SERVICE mode will
most likely result in an abnormally low idle speed or a stalled engine.
Diagnostic Circuit Check. Since this is the starting point for the diagnostic procedures,
always begin here. If the on-board diagnostics are not working, the EFI Diagnostic Cir-
cuit Check will lead to a diagnostic chart in "Diagnostics" to correct the problem. If the
on-board diagnostics are working correctly, go to step 2.
appropriate. This will determine if the fault is still present.
MULTI-PORT FUEL INJECTION DESCRIPTIONS AND SYSTEM OPERATION
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