C175 Petroleum Engine Caterpillar

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

Table 1

J1939 Code and Description	CDL Code and Description	Comments
173-9 Engine Exhaust Gas Temperature : Abnormal Update Rate	2857-9 Engine Exhaust Gas Temperature : Abnormal Update Rate	The alarm output is activated. The code is logged.

Illustration 1	g06361970

Recommended Actions

Table 2

Troubleshooting Test Steps	Values	Results
1. Check for Codes A. Connect Cat® Electronic Technician (ET) to the service tool connector. B. Determine if a code is active or logged.	Codes	Result: A 173-9 code is active or logged. Repair: The Electronic Control Module (ECM) has detected a problem with the communication between the ECM and the sensor. Proceed to Test Step 3. Result: A code is not active or logged. Proceed to Test Step 2.
2. Inspect the Electrical Connectors and the Wiring A. Turn the main disconnect switch to the OFF position. B. Thoroughly inspect the connectors. Refer to Troubleshooting, "Electrical Connectors-Inspect" for additional information. C. Perform a 45 N (10 lb) pull test on the connector wires. D. Check the harness for abrasions and pinch points.	Connectors and Wiring	Result: The connectors and wiring appear to be OK. Proceed to Test Step 3. Result: There is a problem with the connectors and/or wiring. Repair: Repair or replace the connectors or wiring. Ensure that all the seals are properly in place and ensure that the connectors are coupled. If the problem is not resolved, proceed to Test Step 3.
3. Check for Electrical Power at the Harness Connector for the Exhaust Gas Temperature (EGT) Module A. Ensure that the electrical power is removed from the engine. B. Disconnect the harness connector at the EGT module. C. Restore the electrical power to the engine. Set the engine control to STOP. D. Measure the voltage between the following pins at the 70-pin connector for the EGT module: - Pin 6 (+Battery) and Pin 7 (−Battery) E. Remove the electrical power from the engine. F. Restore the wiring to the original configuration.	24 ± 4 V	Result: Voltage at the harness connector for the EGT module is 24 ± 4 V. Repair: The EGT module is receiving the proper operating voltage. Perform the following procedure: 1. Confirm that the 173-9 code is still active. 2. Connect Cat ET. 3. Use Cat ET to monitor the following: - Codes If the 173-9 code is still active, there is a problem in the circuit for the CAN data link. Refer to Troubleshooting, "Data Link -Test" for additional information. If the 173-9 code is no longer active, there is probably an intermittent electrical problem in one of the power circuits. Refer to Troubleshooting, "Electrical Connectors - Inspect" for additional information. Proceed to Test Step 4. Result: Voltage at the harness connector for the EGT module is not 24 ± 4 V. Repair: The EGT module is not receiving the proper operating voltage. There is a problem in the harness or in a connector. Determine the cause of the excessive voltage drop. Perform the necessary repairs. If the problem is not resolved, proceed to Test Step 4.
4. Check the Resistance of the Data Link A. Restore the electrical power to the engine. Set the engine control to STOP B. Measure the resistance between the following EGT module connector locations: - Pin 8 (Global CAN data link +) and Pin 9 (Global CAN data link -)	60 ± 10 Ohms	Result: The resistance is less than 50 Ohms. There are more than 2 termination resistors installed in the wiring harness or a short circuit has been detected. Repair: Repair or replace damaged components. Verify that the repair eliminated the problem. Result: The resistance is 60 ± 10 Ohms. The termination resistors are OK. Verify that the repair eliminated the problem. Result: The resistance is approximately 120 ± 10 Ohms. There is a problem with a termination resistor or a termination resistor is missing. Repair: Check the resistance on each terminating resistor. Replace the failed termination resistor. Verify that the repair eliminated the problem. Result: The resistance is greater than 130 ohms. There is a problem with the wiring harness between the ECM and the next connection point in the data link wiring. Repair: Repair or replace the wiring harness. 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).