GUIDE AS 2689709 - Caterpillar

Use this procedure to troubleshoot the electrical system if a problem is suspected with the exhaust temperature sensor. The exhaust temperature sensor is a component that is installed by the customer.System OperationA Pulse Width Modulated Sensor (PWM) provides a signal to the Electronic Control Module (ECM) from the exhaust temperature sensor. The sensor receives a 8.0 0.4 VDC regulated voltage from the ECM.The sensor generates a PWM signal that is in a specific range of duty cycle that is sent to the ECM. This range is directly related to the temperature that is sampled by the temperature probe. When the temperature of the sensor probe is 50 °C (122 °F) the duty cycle output of the sensor is 22 percent. When the temperature of the sensor probe is 850 °C (1550 °F) the duty cycle output of the sensor is 88 percent. As the temperature of the probe fluctuates between the minimum and the maximum temperatures, the duty cycle fluctuates on a scale that is directly related to the temperature of the temperature probe.The ECM performs an automatic calibration of this sensor whenever the ECM is powered and the engine has been off for at least five seconds.The ECM provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply of the ECM.
Illustration 1 g01371475
Schematic of the sensor circuit for the PWM sensor
Table 1
Troubleshooting Test Step Values Result
1. Verify that the "Exhaust Temperature Sensor Installation Status" is Programmed Correctly
A. Remove eletrical power from the ECM.
B. Connect Caterpillar Electronic Technician (ET) to the service tool connector.
C. Restore electrical power to the ECM.
D. Establish communication with the ECM.
E. Verify that the "Exhaust Temperature Sensor Installation Status" parameter is programmed to "Installed".
F. Remove electrical power from the ECM. The "Exhaust Temperature Sensor Installation Status" parameter is programmed to "Installed". Result: The "Exhaust Temperature Sensor Installation Status" parameter is programmed correctly.
Proceed to Test Step 2.
Result: The "Exhaust Temperature Sensor Installation Status" parameter is not programmed correctly.
Program the "Exhaust Temperature Sensor Installation Status" parameter.
Illustration 2 g01176458
Location of the ECM connectors that are for the exhaust temperature sensor (left side engine view)
(1) J2/P2 ECM connectors
Illustration 3 g01371895
Location of the sensor connector that is for the exhaust temperature sensor (rear engine view)
(2) Connector for the exhaust temperature sensor
Illustration 4 g01371905
Terminal locations at the P2 ECM connector that are for the exhaust temperature sensor
(P2-29) Digital sensor supply
(P2-39) Exhaust temperature
(P2-92) Digital return
Illustration 5 g01159881
Terminal locations at the connectors for the exhaust temperature sensor
(Terminal A) Digital sensor supply
(Terminal B) Digital return
(Terminal C) Exhaust temperature
Table 2
Troublshooting Test Steps Values Result
2. Inspect the Electrical Connectors and the Wiring
A. Thoroughly inspect connectors (1) and (2). Refer to Troubleshooting, "Electrical Connectors - Inspect" for details that are related to inspection of the electrical connectors.
B. Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the engine interface connector that are associated with the circuit.
C. Check the allen head screw on each ECM connector for the proper torque.