C7 and C9 Marine Engines Caterpillar

Use this procedure to troubleshoot any suspect problems with the marine 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

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 a problem 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 a 03 diagnostic code 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 OK. If the sensor is disconnected at the sensor connector, the absence of pull-up voltage at the sensor connector indicates a problem in the signal wire. 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 may be shorted to another wire in the harness.

Illustration 1	g01230070
Schematic for the marine 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	g01130316
Engine components that are associated with the marine transmission oil temperature sensor (1) J137/P137 connector for the marine transmission oil temperature sensor (2) J2/P2 ECM connectors

2. Thoroughly inspect connectors (2). Inspect the connectors for the sensor (1). Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

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Illustration 3	g01230077
P2 terminals that are associated with the marine transmission oil temperature sensor (P2-93) Return (P2-27) Marine transmission oil temperature (P2-81) +5 VDC

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Illustration 4	g01134372
J137 harness connector for the marine transmission oil temperature sensor (A) Supply (B) Return (C) Signal

3. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the marine transmission oil temperature sensor.

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

5. Check the harness and wiring for abrasions and for pinch points from the marine transmission oil temperature sensor 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 connectors and wiring are OK. Proceed to Test Step 2.

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

  Repair: Repair the wiring and/or the connectors. Replace parts, if necessary. 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 for Active Diagnostic Codes

1. Connect the Caterpillar Electronic Technician (ET) to the service tool connector.

2. Restore the electrical power to the ECM.

3. Monitor the active diagnostic code screen on Cat ET. Check and record any active diagnostic codes.

   Note: Wait at least 30 seconds in order for the diagnostic codes to become active.

4. Look for an 03 diagnostic code or an 04 diagnostic code for the marine transmission oil temperature sensor.

Expected Result:

No diagnostic codes are active.

Results:

• OK - No diagnostic codes are active.

  Repair: The problem may have been related to a faulty connection in the harness. Carefully reinspect the connectors and wiring. Refer to the diagnostic functional test Troubleshooting, "Electrical Connectors - Inspect".

  STOP

• Not OK - An 04 diagnostic code is active. Proceed to Test Step 3.

• Not OK - An 03 diagnostic code is active. Proceed to Test Step 5.

Test Step 3. Check the Supply Voltage at the Harness Connector for the Sensor

1. Remove the electrical power from the ECM.

2. Disconnect the harness connector for the sensor.

3. Restore the electrical power to the ECM.

4. Measure the voltage between terminals A (5 V analog supply) and B (sensor return) at the harness connector for the sensor.

5. Remove the electrical power from the ECM.

6. Connect the sensor's harness 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 4.

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

  Repair: Perform the diagnostic functional test Troubleshooting, "Analog Sensor Supply Circuit - Test".

  STOP

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

1. Remove the electrical power from the ECM.

2. Disconnect the harness connector for the 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 Codes" screen on Cat ET and check for an active 03 diagnostic code for the sensor.

5. Remove the electrical power from the ECM.

Expected Result:

An 03 diagnostic code is now active for the sensor.

Results:

• OK - An 04 diagnostic code was active before disconnecting the sensor. An 03 diagnostic code became active after the sensor was disconnected.

  Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the transmission. 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.Verify that the repair eliminates the problem.

  STOP

• Not OK - The 04 diagnostic code is still present. Leave the sensor disconnected. Proceed to Test Step 6.

Test Step 5. Create a Short at the Harness Connector

1. Remove the electrical power from the ECM.

2. Install a jumper wire between terminals B and C on the harness connector for the sensor.

3. Restore the electrical power to the ECM.

4. Wait at least 30 seconds for activation of the 04 diagnostic code.

   Note: Monitor the "Active Diagnostic Codes" screen on Cat ET before installing the jumper wire and after installing the jumper wire.

5. Remove the jumper wire. Check for an 04 diagnostic code again.

6. Remove the electrical power from the ECM.

Expected Result:

An 04 diagnostic code is active when the jumper wire is installed. An 03 diagnostic code is active when the jumper wire is removed.

Results:

• OK - The engine harness and the ECM are OK.

  Repair: Temporarily connect a new sensor to the harness, but do not install the new sensor in the transmission. 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 03 diagnostic code remains active with the jumper in place. Proceed to Test Step 6.

Test Step 6. 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 circuit at the ECM:

   1. Remove terminal P2-27 (signal).

   2. Remove terminal P2-93 (return).

   3. 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.

      An 03 diagnostic code should be active for the sensor.

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

   1. Install a wire jumper between terminals P2-27 (signal) and P2-93 (return).

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

      An 04 diagnostic code should be active when the wire jumper is installed.

   3. Remove the wire jumper. Return all wiring to the original configuration.

Expected Result:

An 03 diagnostic code is active when the signal wire is removed from the ECM connector. An 04 diagnostic code is active when the signal wire is connected to the return wire.

Results:

• OK - The ECM is working properly. The problem is in the wiring between the ECM and the harness connector. There may be a problem in a connector.

  Repair: Repair the wire and/or the connector. Replace parts, if necessary.Verify that the problem is resolved.

  STOP

• Not OK - One of the following conditions exists: The 03 diagnostic code is not active when the sensor signal wire is disconnected. The 04 diagnostic code is not active when the wire jumper is installed.

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

  STOP