C8.7 and C12.9 Marine Engines Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with a sensor. Also, use this procedure if one of the following diagnostic codes is active or easily repeated.

Table 1

Code and Description	Conditions Which Generate this Code	Comments
110-3 Engine Coolant Temperature : Voltage Above Normal	The ECM detects that the voltage is not in the acceptable range.	The code is logged.
110-4 Engine Coolant Temperature : Voltage Below Normal	The ECM detects that the voltage is not in the acceptable range.	The code is logged.
174-3 Engine Fuel Temperature 1 : Voltage Above Normal	The ECM detects that the voltage is not in the acceptable range.	The code is logged.
174-4 Engine Fuel Temperature 1 : Voltage Below Normal	The ECM detects that the voltage is not in the acceptable range.	The code is logged.

The sensor signal for the passive sensor is routed from the Electronic Control Module (ECM) to terminal 1 of each sensor connector. The sensor return for the passive sensors is routed to the ECM from terminal 2 of each sensor connector.

Illustration 1	g03797399

Table 2

Troubleshooting Test Steps	Values	Results
1. Check for Codes A. Connect Cat® Electronic Technician (Cat ET) to the service tool connector. B. Determine if a code is active or logged.	Codes	Result: A -3 code is active. Proceed to Test Step 2. Result: A -4 code is active. Proceed to Test Step 3. Result: For a code that is logged, but not currently active. Proceed to Test Step 4.
2. Create a Short at the Sensor Connector A. Turn the keyswitch to the OFF position. B. Disconnect the sensor with the active -3 code. C. Install the jumper wire between the following terminals at the sensor connector: - Terminal 1 (sensor signal) and Terminal 2 (sensor return) D. Use Cat ET to monitor the following: - -4 code E. Turn the keyswitch to the OFF position.	Create a Short	Result: The -3 code remains active. The wiring harness is NOT OK. Repair: There is an open in the wiring harness. Repair or replace the wiring harness. Verify that the repair eliminated the problem. Result: A -4 code became active. Repair: The wiring harness is OK. Replace the sensor. Verify that the repair eliminated the problem. If the problem is not resolved, proceed to Test Step 3.
3. Create an Open at the Sensor Connector A. Turn the keyswitch to the OFF position. B. Disconnect the sensor with the active -4 code. C. Use Cat ET to monitor the following: - -3 code Note: For a 110-3 code, start the engine and let the engine idle for 7 minutes. The engine must be running for at least 7 minutes in order for the diagnostic to run. D. Turn the keyswitch to the OFF position.	Create an Open	Result: The -4 code remains active. The wiring harness is NOT OK. Repair: There is an open in the wiring harness. Repair or replace the wiring harness. Verify that the repair eliminated the problem. Result: A -3 code became active. Repair: The wiring harness is OK. Replace the sensor. Verify that the repair eliminated the problem. If the problem is not resolved, proceed to Test Step 4.
4. Perform the Wiggle Test Carefully following this procedure is the best way to identify the root cause of an intermittent problem. A. Use CAT ET to perform the following test: - "Wiggle Test" B. Slowly wiggle the wiring and the connectors between the P2 connector and the sensor. Slowly wiggle the wiring and the connectors between the P1 connector and the sensor. Pay particular attention to the wiring near each connector. Be sure to wiggle all of the wiring. C. As you wiggle the wiring look for the following problems: - Loose connectors or damaged connectors - Moisture on the connectors or the wiring - Damage that is caused by excessive heat - Damage that is caused by chafing - Improper routing of wiring - Damaged insulation	Test	Result: The wiring is NOT OK. Repair: There is a problem with the wiring harness. Repair or replace the wiring harness. Verify that the repair eliminated the problem. Result: The wiring is OK. Repair: The problem may be intermittent. Inspect the wiring harness. Refer to Troubleshooting, "Electrical Connectors - Inspect" for additional information. If the wiring looks OK perform the following procedure. 1. Turn the keyswitch to the OFF position. 2. Disconnect the connectors. Carefully inspect the terminals for proper installation. Make sure that each terminal is clean and dry. 3. Insert a pin into each socket. Verify that each socket grips the pin firmly. Repair any problems. 4. Connect all connectors. 5. Verify that the repair eliminated the problem.

If the procedure did not correct the issue, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).