Step Diagnostic Process Details Yes No
9
Turn the key switch to the run
position. Disconnect the warning horn
brown lead. Temporarily ground the
warning horn brown lead.
Does the warning horn sound?
The horn must sound anytime the
purple lead has battery voltage and
the brown lead is grounded.
Go to step 10.
Replace the warning horn
and retest.
10
Test the circuit between the helm
harness brown warning horn
connector and the engine harness
brown/blue lead at PCM 112
connector A, pin 1E for continuity.
Does the circuit have continuity?
The PCM grounds this circuit to
sound the warning horn. The circuit
changes from brown (boat) to brown/
blue (engine) at the 14‑pin engine
connector.
Go to step 11.
Repair or replace the
defective circuit between
the warning horn and
PCM 112.
11
Test PCM 112 connector B, pin 4G for
battery voltage when the key switch is
in the run position.
Is the voltage within 1.0 V of
battery?
The PCM 112 turns on when it sees
battery voltage at this pin.
Go to step 12.
Repair the purple wake
circuit.
12
Test for battery voltage between the
positive terminal of the battery and
each of the following PCM 112
connector pins: A‑4C, C‑1G, and
C‑2G.
Does each circuit measure within
1.0 V of battery?
– Go to step 13.
Repair or replace the
defective PCM 112
ground circuit.
13
Does the engine system power up?
If the engine system does not power
up after successfully completing all of
the previous steps, there may be a
problem with the PCM 112.
Go to step 14.
Call MerCruiser Service
for assistance.
14
Does the OBD‑M lamp self‑test?
The OBD‑M lamp should complete a
self‑test on engine system power up.
The engine
system is now
powering up
properly. Return
to the
Diagnostic
Roadmap and
continue with
step 2.
Go to Chart R2.
Chart R2: OBD‑M Lamp Does Not Self‑Test
This procedure is intended to diagnose an OBD‑M lamp that does not self‑test. You are here because you answered no to step
14 in Chart R1.
If the engine is equipped with an OBD‑M indicator lamp, it must complete a self‑test each time the system is turned on. Failure
to self‑test is an indication that the light is not working and cannot be used to indicate the status of the emissions control
system. Use the following table to diagnose an OBD‑M lamp that does not self‑test.
Step
Diagnostic Process Details Yes No
1
Turn the key switch to the run
position. Check for battery voltage at
the white lead at the OBD‑M lamp.
Is the voltage within 1.0 V of
battery?
The key switch purple lead connects to
the engine harness through the 14‑pin
main data harness and connectors. It
changes color from purple (engine side) to
white (OBD‑M light harness) at the
engine's 2‑pin OBD‑M light connector.
The white lead is the positive side of the
light.
Go to step 2.
Check the engine's
2‑amp OBD‑M
lamp fuse. Repair
or replace the
circuit between the
key switch purple
lead and the
OBD‑M lamp white
lead.
Troubleshooting
Page 1D-6 © 2016 Mercury Marine 90-8M0099748 eng DECEMBER 2015
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