SPN 177 - FMI 3 (Diagnostic Code: Transmission Oil Temperature Sensor - Voltage Above Normal)
Transmission Sump Oil Temperature
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| Figure 1.1 - Transmission Hyd. Control Valve (TH55) |
MID 027 CID 0177 FMI 03
#Conditions Which Generate this Code
This Diagnostic Code is associated with the Transmission Oil Temperature Sensor. This Diagnostic Code is recorded when the ECM reads the signal from the Transmission Oil Temperature Sensor
as being shorted to the +Battery. The sensor produces a PWM signal.
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| Figure 1.2 - Connections of the Transmission Oil Temp. Sensor |
→The supply circuit to the sensor is open.
→The return circuit is open.
→The signal circuit is shorted to the +Battery.
→The signal circuit is open or the sensor is disconnected.
→The sensor has failed.
→The ECM has failed. This is unlikely
NOTE: Ensure that CID 0177 FMI 03 is active. This procedure can cause new Diagnostic Codes to
be recorded. Ignore these created Diagnostic Codes. When the procedure is completed, clear the
created Diagnostic Codes.
Test Step 1. CHECK THE VOLTAGE AT THE SENSOR
A). Turn the disconnect switch and the key start switch to the ON position.
B). Disconnect the sensor from the machine harness.
C). At the machine harness connector for the sensor, measure the voltage between contact A
(wire R800-OR/Orange) and contact B (wire R998-BR/Brown).
Expected Result:
The voltage should measure approximately 8 VDC.
Results:
→OK - The voltage is approximately 8 VDC. Proceed to Test Step 4.
→NOT OK - The voltage is not approximately 8 VDC.
→Repair: There is a problem with the machine harness or the ECM has failed. It is unlikely
that the ECM has failed. Proceed to Test Step 2.
Test Step 2. CHECK FOR AN OPEN IN THE SUPPLY CIRCUIT
A). The key start switch and the disconnect switch remain in the ON position.
B). The sensor remains disconnected from the machine harness.
C). At the machine harness connector for the sensor, measure the voltage from contact A (wire
R800-OR/Orange) to ground.
Expected Result:
The voltage should measure approximately 8 VDC.
Results:
→OK - The voltage measurement is approximately 8 VDC. Proceed to Test Step 3.
→NOT OK - The voltage does not measure approximately 8 VDC.
→Repair: The supply circuit is not correct. Repair the circuit or replace the circuit.
STOP
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| Figure 1.3 - Voltage Above Normal (177-3) |
Test Step 3. CHECK FOR AN OPEN IN THE RETURN CIRCUIT
A). Turn the key start switch and the disconnect switch to the OFF position.
B). The sensor remains disconnected from the machine harness.
C). Disconnect the machine harness connector J1 from the ECM
D). At the machine harness connector for the sensor, install a jumper wire from contact B (wire
R998-BR/Brown) to ground.
E). At the machine harness connector for the ECM, measure the resistance from contact J1-45
(wire R998-BR/Brown) to ground.
Expected Result:
The resistance measurement should measure less than 5K ohms.
Results:
→OK - The resistance measurement is less than 5K ohms. The harness is correct.
→Repair: Check the circuit again, use the Cat ET to perform a Wiggle Test on the machine wiring harness. The Wiggle Test can detect shorts and opens in the machine wiring harness that are
momentary or intermittent. Read More: Wiggle Test on Caterpillar ET Software. It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If
the cause of the Diagnostic Code is not found, replace the ECM. STOP
→NOT OK - The resistance that is measured is not correct.
→Repair: There is an open in the machine harness. The open is in the return circuit with the
high resistance measurement. Repair the harness or replace the harness. STOP
Test Step 4. CHECK FOR AN OPEN IN THE SIGNAL CIRCUIT
A). Turn the key start switch and the disconnect switch to the OFF position.
B). Disconnect the J1 and J2 machine harness connector from the ECM.
C). At the machine harness connector for the sensor, install a jumper wire from contact C (wire
428-OR/Orange) to contact B (wire R998-BR/Brown).
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| Figure 1.4 - Transmission Oil Temp. Sensor (Jumper/B and C) |
D). At the machine harness connector J1, measure the resistance from contact J2-25 (wire 428
OR/Orange) to contact J1-45 (wire R998-BR/Brown).
Expected Result:
The resistance should measure less than 5K ohms.
Results:
→OK - The resistance measures less than 5K ohms. Proceed to Test Step 5.
→NOT OK - The resistance measurement is greater than 5K ohms.
→Repair: There is an open in the signal circuit. Repair the harness or replace the harness.
STOP
Test Step 5. CHECK THE SIGNAL CIRCUIT FOR A SHORT
A). The disconnect switch and the key start switch remain in the OFF position.
B). The machine harness connectors J1 and J2 remain disconnected.
C). Remove the jumper wire from contact C (wire 428-OR/Orange) to contact B (wire R998
BR/Brown).
D). At the J1 and J2 machine harness connectors for the ECM, measure the resistance for the
signal contact of the sensor J2-25 (wire 428-OR/Orange) to all other J1 and J2 contacts.
Expected Result:
Each resistance measurement should be greater than 5K ohms.
Results:
→OK - Each resistance measurement is greater than 5K ohms. The sensor has failed.
Replace the sensor (Cat P/N 134-2252) and verify that the new sensor corrected the problem. If the problem
persists, exit this procedure and perform this procedure again.
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| Figure 1.5 - Transmission Oil Temp. Sensor (134-2252) |
→Repair: Check the circuit again, use the Cat ET to perform a Wiggle Test on the machine wiring harness. The Wiggle Test can detect shorts and opens in the machine wiring harness that are
momentary or intermittent. It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. If
the cause of the Diagnostic Code is not found, replace the ECM.
Read More:
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| Figure 1.6 - Transmission Oil Temperature (109 deg F) |
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