3512C Petroleum Engines with Dynamic Gas Blending Caterpillar

Use this procedure to troubleshoot a problem with the exhaust temperature sensors. Also, use this procedure if the following diagnostic code is active or easily repeated.

Table 1

Diagnostic Codes Table
J1939 Code and Description	Conditions which Generate this Code	System Response
173-9 Engine Exhaust Gas Temperature : Abnormal Update Rate	The Integrated Sensor Module (ISM) has not received several messages that were expected from the exhaust temperature sensors over the CAN data link.	The code is logged. The alarm output is activated.

The ISM is an electronic monitoring system used to monitor exhaust temperatures. The module monitors the following thermocouples:

• Thermocouple for the exhaust port of each cylinder

The ISM reads each of these temperatures and sends this information via the CAN data link to the ECM and the optional remote control panel.

If the ECM cannot communicate with the ISM, the ECM activates a diagnostic code related to identify the problem. The most likely cause of the diagnostic code is a problem with an electrical connector or a harness. The next likely cause is a problem with the ISM.

Terminating resistors must be connected to each end of the CAN data link. The terminating resistors improve the communication signal between the devices. If there is an intermittent diagnostic code for any of the devices connected to the CAN data link, check the terminating resistors. One of the terminating resistors is in the control panel. The other terminating resistor is inside the ECM control box. If the engine is not equipped with a remote panel, the other terminating resistor will be connected at the far end of interconnect harness. Refer to Troubleshooting, "CAN Data Link - Test" for details related to troubleshooting the data link circuit.

This troubleshooting procedure may generate additional diagnostic codes. Correct the cause of the original diagnostic code before continuing. You clear the diagnostic codes after the problem is resolved.

Illustration 1	g03818797

Illustration 2	g03382427
(1) ISM P1/J1 (2) ISM P2/J2

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 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. Ensure that the electrical power has been removed from the engine. 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 of 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 ISM A. Ensure that the electrical power is removed from the engine. B. Disconnect the harness connector at the Integrated Sensing Module (ISM). 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 ISM. - Pin 66 (−Battery) and Pin 68 (+Battery) - Pin 67 (−Battery) and Pin 69 (+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 ISM module is 24 ± 4 V. Repair: The ISM 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, "CAN 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 ISM is not 24 ± 4 V. Repair: The ISM 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 of the following global CAN data link pins at the ISM. - Pin 50 (Global CAN data link +) and Pin 48 (Global CAN data link -) C. Measure the resistance of the following local CAN data link pins at the ISM. - Pin 61 (Local CAN data link +) and Pin 51 (Local 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).