Chart R1: Engine System Fails to Power Up
This procedure is intended to diagnose a PCM 112 system that does not turn on. You are here because you answered no to
step 1 of the diagnostic roadmap.
The PCM 112 receives continuous battery power and ground through a special 2‑wire PCM power harness that contains a
5‑amp fuse. The helm is powered separately through the battery cables. This circuit includes the 90‑amp block fuse, the
50‑amp circuit breaker, and a 20‑amp fuse.
The remainder of the engine harness receives battery power through the battery cables, which may or may not be connected to
a battery switch. If the key switch is turned to the run position while the battery switch is off, diagnostic faults will be set.
Step Diagnostic Process Details Yes No
1
Are the battery switches set for
normal operation?
Not all boats will have a battery
switch. They are optional.
Go to step 2.
Reset the switches for
normal operation.
2
Check the condition and state of
charge of the main engine battery.
Is the battery serviceable?
Refer to the engine service manual
for battery specifications.
Go to step 3.
Charge or replace the
battery.
3
Check the battery cable connections
at both the engine and battery.
Are the battery connections good?
Ensure that the ground stud is
tightened securely in the engine
block. Ensure that corrosion‑resistant
hex nuts are used instead of
wingnuts.
Go to step 4.
Clean and tighten all
connections.
4
Check the 5‑amp PCM power fuse,
and check for correct routing of the
PCM power circuit.
Is the fuse good and the harness
routing correct?
The PCM power harness must be
connected directly to the main engine
battery. It cannot be connected to a
battery switch. The PCM power
harness connects the battery to a
2‑pin engine harness connector.
Go to step 5.
Replace the fuse.
Reroute or reconnect the
harness as necessary.
Install the harness if it is
missing.
5
Check for battery voltage at the red
lead of the helm harness key switch
connector.
Is the voltage within 1.0 V of
battery?
Voltage must be present
continuously, regardless of battery
switch position. If the main engine
battery is connected, voltage must be
present.
Go to step 6.
Repair or replace circuit.
This circuit includes the
battery cable, 90‑amp
block fuse, 50‑amp circuit
breaker, and a 20‑amp
fuse. It includes the red
lead in pin A of the 14‑pin
connectors on the
engine, main data
harness, and helm
harness.
6
Turn the key switch to the run
position. Check for battery voltage at
the purple lead of the helm harness
key switch connector.
Is the voltage within 1.0 V of
battery?
Voltage must be present when the
key switch is in the run position, but
not when the key switch is in the off
position.
Go to step 7.
Replace the key switch,
as necessary.
7
Check the battery voltage between
the black lead of the helm harness
key switch connector and the positive
terminal of the main engine battery.
Is the voltage within 1.0 V of
battery?
Voltage must be present
continuously. This test verifies the
ground circuits between the PCM
power harness and the helm.
Go to step 8.
Repair or replace circuit.
This circuit includes the
battery, PCM power
harness black lead,
14‑pin main harness
black lead, and helm
harness to the key switch
black lead.
8
Turn the key switch to the run
position. Check for battery voltage at
the warning horn purple lead.
Is the voltage within 1.0 V of
battery?
– Go to step 9.
Repair or replace the
purple circuit between the
key switch and the
warning horn.
Troubleshooting
90-8M0099748 eng DECEMBER 2015 © 2016 Mercury Marine Page 1D-5
To Next Page
Loading...
Need help?
General