3126B Marine Engines Caterpillar

Use this procedure to troubleshoot any suspect problems with the transmission oil temperature sensor.

This procedure covers the following diagnostic codes:

• 177-03 Transmission Oil Temperature open/short to +batt

• 177-04 Transmission Oil Temperature short to ground

The Electronic Control Module (ECM) supplies 5.0 ± 0.2 VDC to terminal A of each sensor. The sensor common connection is connected to terminal B of each sensor. The signal voltage from terminal C of each sensor is sent to the appropriate terminal on the ECM.

Pull-up Voltage

The ECM continuously outputs a pull-up voltage on the circuit for the sensor signal wire. The ECM uses this pull-up voltage in order to detect an open in the signal circuit. When the ECM detects the presence of a voltage that is above a threshold on the signal circuit, the ECM will generate an open circuit diagnostic code (-03) for the sensor.

If the sensor is disconnected at the sensor connector, the presence of pull-up voltage at the sensor connector indicates that the wires from the sensor connector to the ECM are not open or shorted to ground. If the sensor is disconnected at the sensor connector, the absence of pull-up voltage at the sensor connector indicates an open in the signal wire or a short to ground. If the sensor is disconnected at the sensor connector and the voltage at the sensor connector is different from pull-up voltage, the signal wire is shorted to another wire in the harness.

Illustration 1	g01193046
Schematic for the transmission oil temperature sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Remove the electrical power from the ECM.

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Illustration 2	g01192174
Typical location of the engine's transmission sensors (1) Connector for the transmission oil pressure sensor (2) Connector for the transmission oil temperature

2. Thoroughly inspect connectors (1) and (2). Refer to diagnostic functional tests Troubleshooting, "Electrical Connectors - Inspect" for details.

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Illustration 3	g01094223
P2 ECM connector for transmission oil temperature sensor (P2-17) Transmission oil temperature sensor signal (P2-42) Sensor return (P2-41) +5 V sensor supply

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Illustration 4	g01094844
Terminals for the temperature sensor

3. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the sensor connectors that are associated with the active diagnostic code.

4. Check the allen head screw for each ECM connector for the proper torque. Refer to diagnostic functional tests Troubleshooting, "Electrical Connectors - Inspect" for the correct torque value.

5. Check the harness and wiring for abrasions and for pinch points from the sensor back to the ECM.

Expected Result:

All connectors, pins, and sockets are completely coupled and/or inserted. The harness and wiring are free of corrosion, of abrasion, and of pinch points.

Results:

• OK - The harness and wiring appear to be OK. Proceed to Test Step 2.

• Not OK - There is a problem in the connectors and/or wiring.

  Repair: Repair the connectors or wiring and/or replace the connectors or wiring. Ensure that all of the seals are properly in place and ensure that the connectors are completely coupled.Verify that the repair eliminates the problem.

  STOP

Test Step 2. Check the Supply Voltage at the Sensor Connector

1. Remove the electrical power from the ECM.

2. Disconnect the transmission oil temperature sensor at the sensor connector:

3. Restore the electrical power to the ECM.

4. Measure the voltage between the terminal for the +5 V supply and the terminal for the sensor return at the harness side of the sensor connectors.

5. Remove the electrical power from the ECM.

6. Connect all sensor connectors.

Expected Result:

The voltage is 5.0 ± 0.2 VDC.

Results:

• OK - The voltage is 5.0 ± 0.2 VDC. The voltage is correct. Proceed to Test Step 3.

• Not OK - The voltage is not 5.0 ± 0.2 VDC.

  Repair: The voltage is incorrect. Refer to diagnostic functional tests Troubleshooting, "Analog Sensor Supply Circuit - Test".

  STOP

Test Step 3. Check for Active Diagnostic Codes

1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector. Refer to electronic troubleshooting Troubleshooting, "Electronic Service Tools".

2. Restore the electrical power to the ECM.

3. Use Cat ET to check for active diagnostic codes. Wait at least 30 seconds so that any codes may become active. Look for an active diagnostic code for the transmission oil temperature sensor.

4. Check for the following active diagnostic codes:
   • 177-03

   • 177-04

Expected Result:

No diagnostic codes are active for the transmission oil temperature sensor.

Results:

• OK - No diagnostic codes are active for the transmission oil temperature sensor.

  Repair: The problem may have been related to a faulty connection in the harness. Carefully inspect the connectors and wiring for problems that could cause an intermittent problem. Refer to diagnostic functional tests Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - The 177-04 diagnostic code is active at this time. Proceed to Test Step 4.

• Not OK - The 177-03 diagnostic code is active at this time. Proceed to Test Step 5.

Test Step 4. Disconnect the Sensor in Order to Create an Open Circuit

1. Turn the keyswitch to the OFF position.

2. Disconnect the connector for the transmission oil temperature sensor.

3. Restore the electrical power to the ECM. Wait at least 30 seconds for activation of the diagnostic codes.

4. Access the "Active Diagnostic Code" screen on Cat ET. Check for an active 177-03.

5. Remove the electrical power from the ECM.

Expected Result:

The 177-03 diagnostic code is now active.

Results:

• OK - The 177-04 diagnostic code was active before disconnecting the sensor connector. A 177-03 diagnostic code became active after disconnecting the sensor.

  Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.

  STOP

• Not OK - There is a short circuit between the sensor harness connector and the ECM. Leave the sensor disconnected. Proceed to Test Step 8.

Test Step 5. Check the Pull-up Voltage at the Sensor Connector

1. Restore the electrical power to the ECM.

2. Measure the voltage between the terminal for the transmission oil temperature sensor signal and the terminal for the sensor return at the harness side of the sensor connector.

3. Remove the electrical power from the ECM.

Expected Result:

The voltage is 11 ± 2 VDC.

Results:

• OK - The voltage is within specifications.

  Repair: The signal wire to the ECM from the sensor connector is OK. The open circuit is in the sensor or the wire between the sensor and the sensor connector. Replace the sensor. Do not install the sensor in the engine. Verify that no diagnostic codes are active for the sensor before permanently installing the sensor.

  STOP

• Not OK - The voltage is not within specifications. Proceed to Test Step 6.

Test Step 6. Check the Signal Wire for a Short Circuit

1. Remove the electrical power from the ECM.

2. Disconnect the J2/P2 (ECM connectors).

3. Disconnect the connector for the transmission oil temperature sensor.

4. Measure the resistance between the terminal for the sensor signal wire at the ECM and every terminal on the P2 ECM connector.

5. Connect the J2/P2 (ECM connectors).

Expected Result:

The resistance measurement indicates an open circuit for each measurement.

Results:

• OK - Each resistance measurement indicates an open circuit. Proceed to Test Step 7.

• Not OK - At least one resistance measurement does not indicate an open circuit.

  Repair: There is a problem in the wiring for the sensor. There may be a problem with a connector. Repair the wiring and/or the connector. Replace parts, if necessary.

  STOP

Test Step 7. Create a Short at the Harness Connector for the Sensor

1. Remove the electrical power from the ECM.

2. Fabricate a jumper wire that can be used to short the terminal for the sensor return and the terminal for the sensor signal. Install the jumper on the harness side of the connector.

3. Restore the electrical power to the ECM.

4. Monitor the "Active Diagnostic Codes" screen on Cat ET before installing the jumper wire and after installing the jumper wire. Wait at least 30 seconds for activation of 177-04.

   Note:

5. Remove the jumper wire.

6. Remove the electrical power from the ECM.

Expected Result:

A 177-04 is active when the jumper wire is installed. A 177-03 is active when the jumper wire is removed.

Results:

• OK - The active diagnostic code changed from a 04 to a 03, as described above.

  Repair: The engine harness and the ECM are OK. Temporarily connect a new sensor to the harness, but do not install the new sensor in the engine. Verify that there are no active diagnostic codes for the sensor. If there are no active diagnostic codes for the sensor, permanently install the new sensor. Clear any logged diagnostic codes.

  STOP

• Not OK - The open circuit diagnostic code 03 remains active with the jumper in place. The open circuit is between the ECM and the sensor connector. Proceed to Test Step 8.

Test Step 8. Check the Operation of the ECM

1. Remove the electrical power from the ECM.

2. Check the operation of the ECM by creating an open at the ECM connector.

   1. Disconnect the J2/P2 ECM connectors.

   2. Remove terminals P2-17 (transmission oil temperature sensor signal) and terminal P2-42 (sensor return) from the J2/P2 ECM connector.

      Note: Disconnecting the sensor return from the ECM will generate an open circuit diagnostic code for all sensors that are connected to the sensor return. Troubleshoot the original diagnostic code. Delete the logged diagnostic codes when you are finished.

   3. Connect the J2/P2 (ECM connectors).

   4. Restore the electrical power to the ECM. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 30 seconds for activation of the code.

      Check for an active 177-03.

3. Check the operation of the ECM by creating a short at the ECM.

   1. Install a wire jumper between terminals P2-17 (transmission oil temperature sensor signal) and terminal P2-42 (sensor return) at the J2/P2 ECM connector.

   2. Monitor the "Active Diagnostic Code" screen on Cat ET. Wait at least 30 seconds for activation of the code.

      Check for an active 177-04.

   3. Remove the wire jumper and return the wiring to the original configuration.

Expected Result:

The 177-03 diagnostic code is active when the sensor signal wire is removed from the ECM connector. A 177-04 diagnostic code is active when the signal wire is shorted to the sensor return.

Results:

• OK - The ECM is operating properly. The problem is in the wiring between the ECM and the sensor connector.

  Repair: If the code is active for more than one sensor, the problem is most likely in the return wire for the sensor. Repair the return wire for the sensor or replace the harness.If the code is only active for the transmission oil temperature sensor, the problem is most likely in the signal wire for the sensor. Repair the signal wire for the sensor.

  STOP

• Not OK - The diagnostic codes did not become active according to the expected result of the test.

  Repair: Replace the ECM. Refer to electronic troubleshooting Troubleshooting, "Replacing the ECM". Verify that the problem is resolved.

  STOP