Mercury MERCRUISER, Service Manual, Page: 346 / 566

Testing the Audio Warning System
1. Turn the key switch to the on position without cranking the engine.
2. Listen for the audio alarm. The alarm will sound if the system is functioning correctly.
Guardian Strategy
The MerCruiser Engine Guardian system reduces the potential for engine damage by restricting engine power when the PCM
detects a potential problem. Below are some examples of what Engine Guardian monitors:
•
Oil pressure
• Engine overspeed
• Exhaust manifold temperature
IMPORTANT: Engine Guardian can reduce power anywhere from 100% to idle, depending on the severity of the problem. If
forced to idle, boat speed might not respond to throttle operation.
The PCM stores the fault for diagnostics. For example, if the water inlet becomes partially blocked, Engine Guardian reduces
the available power level of the engine to help prevent damage from decreased water flow to the engine. If the debris passes
through, and full water flow is restored, Engine Guardian restores engine power to normal.
Wiring Diagrams
Transom Harness—MPI
a - MerCathode
b - Digital trim sensor
c - Ground to transom
d - Pitot sensor
e - Steering sensor
f - MerCruiser control
(not needed if use
Outboard control)
g - To trim pump
h - MerCruiser control
(not needed if use
Outboard control)
i - MerCruiser control
(not needed if use
Outboard control)
j - Engine
a
b
c
d
e
f
g
h
i
j
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Instrumentation and Controls
Page 4D-16 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015