
100 RENR9348-01
Troubleshooting Section
Results:
•
OK –Thevoltageis24±3VDCwhentheengine
speed increases above 75 percent of the rated
engine speed.
The ECM and the wiring to the
air shutoff relay are OK. The problem is with the
air shutoff relay’s secondary circuit or the relay.
Proceed to Te
st Step 8.
•
Not OK – The voltage is not 24 ± 3 VDC when
the engine sp
eed increases above 75 percent of
the rated engine speed. There is a problem in the
circuit between the ECM and the air shutoff relay.
There may be a
problem with the ECM. Proceed
to Test Step 7.
Test Step 7. C
heck the ECM Output for
the Air Shut
off Relay at the ECM
A. Disconnect J1/P1 ECM connector.
B. Fabricate a jumper wire that is long enough to
use as a test lead at the ECM connector. Crimp a
connector
socket to one end of the jumper wire.
C. Remove the wire from terminal location P1-10 (air
shutoff) a
t the ECM connector. Install the jumper
wire into thi s terminal location.
D. Connect th
e J1/P1 ECM connectors.
E. Start the engine.
F. Use Cat ET to activate the “Overspeed Verify”
feature. Wait at least 30 seconds for activation of
the featu
re.
G. Increase engine speed to the rated speed of the
engine.
H. As the engine speed increases above 75 percent
of the rat
ed engine speed, measure the voltage
between the loose wire at the air shutoff relay and
theenginegroundstud.
Note: TheECMappliesavoltagetothecircuitfor
approximately one second. Run the test as many
timesasn
ecessary in order to verify that a voltage
is present at this output. The emergency stop switch
must be reset before the test can be run again.
I. Stop the engine.
Turn the
battery disconnect switch to the OFF
position.
Restore
the wiring to the original configuration.
Expected Result:
As the engine speed increases above 75 percent of
the rated engine speed, the voltage is 24 ± 3 VDC.
Results:
•
OK – The voltag
eis24±3VDCwhentheengine
speed increases above 75 percent of the rated
engine speed.
Repair: Thereisanelectricalprobleminthe
harness between the ECM and the air shutoff
relay. The pr
oblem may be in a connector. Repair
the harness and/or the connectors. Replace parts,
if necessary. Verify that the original problem is
resolved.
STOP.
•
Not OK – The voltage is 24 ± 3 VDC when the
engine speed increases above 75 percent of the
rated engin
e speed.
Repair: The ECM is not responding to the
overspeed c
ondition. There is a problem with the
ECM. Replace the ECM. Refer to the electronic
troubleshooting procedure Troubleshooting,
“Replacing
the ECM” for information that is related
to ECM replacement.
STOP.
Test Step 8. Check the Relay Output at
the Air Shutoff Solenoids
A. Remove the supply wires from the terminals of
each air shutoff solenoid.
B. Start the engine.
C. Use Cat ET
to activate the “Overspeed Verify”
feature. Wait at least 30 seconds for activation of
the feature.
D. Increase engine speed to the rated speed of the
engine.
E. As the engine speed increases above 75 percent
of the rated engine speed, measure the voltage
between
the supply wires for the air shutoff
solenoids and the engine ground stud.
Note: Th
e ECM applies a voltage to the circuit for
approximately one second. Run the test as many
times as necessary in order to verify that a voltage
is prese
nt at this output. The emergency stop switch
must be reset before the test can be run again.
F. Stop the
engine.