Mercury MERCRUISER - Chart R3: Crankshaft Fails to Rotate

Step Diagnostic Process Details Yes No
2
Disconnect the black lead from the
OBD‑M lamp. Turn the key switch to
the run position. Ground the OBD‑M
lamp's empty terminal with a suitable
jumper wire.
Does the OBD‑M lamp light when
grounded?
The black lead is the negative side of the
light.
Go to step 3.
Replace the
defective OBD‑M
lamp.
3
Test the circuit between the OBD‑M
lamp black lead and the PCM 112
connector A, pin 1F for continuity.
Does the circuit have continuity?
The OBD‑M light black lead connects
directly to the engine harness. It changes
to light blue in the engine harness, across
the 2‑pin OBD‑M light connector. The
PCM grounds this circuit to turn on the
OBD‑M lamp.
Go to step 4.
Repair or replace
the defective
circuit.
4
Does the OBD‑M lamp self‑test
when the key switch is turned to
the run position?
If the OBD‑M lamp does not self‑test after
successfully completing all of the previous
steps, there may be a problem with the
PCM 112.
The lamp is
working correctly.
Return to the
Diagnostic
Roadmap and
continue with step
2.
Call Mercury
Product Service.
Chart R3: Crankshaft Fails to Rotate
This procedure is intended to diagnose a PCM 112 mechanical shift engine that does not rotate the crankshaft when the key
switch is held in the start position. You are here because you answered no to step 3 of the diagnostic roadmap.
The key switch controls the starter relay on the engine. The starter relay controls the starter solenoid (mounted on the starter
motor). The starter solenoid sends heavy current from the battery through the starter motor. The PCM 112 does not control any
of these functions, everything is mechanical. The engine will continue to crank until the key switch is released.
All MerCruiser engines are designed to use a neutral safety switch. The switch is inside the remote control on sterndrive
engines and mounted to the transmission on inboard engines. The switch must be closed when in neutral, and open when in
gear.
Step
Diagnostic Process Details Yes No
1
Is the remote control in the neutral,
idle position?
The remote control must be in
neutral for the engine to start.
Go to step 2.
Reposition the
control levers.
2
Are all battery switches set for
normal operation?
Not all boats will have a battery
switch. They are optional.
Go to step 3.
Reset the switches
for normal operation.
3
Check the main engine battery rating,
condition, and state of charge.
Is the battery good for this
application?
A weak battery may engage the
relay or solenoid, but not crank
the engine.
Go to step 4.
Charge, retest, or
replace the battery.
4
Check the battery cable connection at
both the engine and battery.
Are the connections good?
Ensure that the ground stud is
tightened securely in the engine
block. Ensure that the battery
wingnuts have been replaced
with corrosion‑resistant hex nuts.
Go to step 5.
Clean and tighten all
connections.
5
Does the starter motor make any
sound when the key switch is
turned to start?
If the starter motor energizes and
spins, it will make an audible
noise. (The exact noise it makes
can be a further clue to an
experienced technician.)
Go to step 10. Go to step 6.
6
Does the starter solenoid click
when the key switch is turned to
start?
The starter solenoid will produce
an audible click as it engages.
Go to step 10. Go to step 7.
7
Check all engine fuses and the circuit
breaker.
Are all fuses and the circuit
breaker good?
Check the 90‑amp block fuse,
50‑amp circuit breaker, and the
15‑amp and 20‑amp engine
fuses.
Go to step 8.
Reset or replace as
necessary.
Troubleshooting
90-8M0099748 eng DECEMBER 2015 © 2016 Mercury Marine Page 1D-7