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Page Title:
Test Step 3. Use an Electronic Service Tool to Check the ECM Tachometer Signal |
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 402
TM 9-2320-312-24-2
Troubleshooting Section
Result 3 The engine rpm is not within 50 rpm
Expected Result:
of 1500 rpm. Proceed to Test Step 5.
Wires are connected to the ECM terminals for the
tachometer, P1:39 (Tachometer-) and/or P1: 38
(Tachometer+).
Results:
OK The ECM is providing the signal for the
tachometer. Proceed to Test Step 3.
Not OK The ECM is not connected in order to
supply the signal to the tachometer.
Repair: Send the vehicle to the OEM dealer in
order to repair the tachometer circuit.
STOP.
Test Step 3. Use an Electronic Service
Tool to Check the ECM Tachometer
Signal.
A. Connect the electronic service tool at the cab
data link connector.
B. Turn the ignition key switch to the ON position.
following display screens in order:
"Diagnostics"
"Diagnostic Tests"
"Special Test"
D. While the dash tachometer is being monitored,
begin the test.
Expected Result:
RESULT 1 The dash tachometer indicates
approximately 1500 150 rpm and the dash
tachometer is stable.
RESULT 2 The tachometer does not indicate an
engine rpm or the tachometer is erratic.
RESULT 3 The tachometer rpm is stable but the
tachometer rpm is not within 50 rpm of 1500 rpm.
Results:
Result 1 The ECM and the tachometer are OK.
STOP.
Result 2 The engine rpm is not indicated or the
engine rpm is erratic. Proceed to Test Step 4.
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