Use this procedure to troubleshoot the electrical system if a problem is suspected with the exhaust temperature sensors or if any of the diagnostic codes in Table 1 is active or easily repeated.
The exhaust temperature sensors are components that are installed by the customer.
| Diagnostic Codes Table | ||
|---|---|---|
| Code and Description | Conditions which Generate this Code | System Response |
| 827-8 Left Exhaust Temperature Sensor abnormal frequency, pulse width, or period | The Electronic Control Module (ECM) detects a sensor frequency that is greater than 600 Hz or less than 400 Hz. The ECM detects a duty cycle that is greater than 88 percent or a duty cycle that is less than 22 percent. |
The ECM flags the exhaust temperature as invalid data. |
| 828-8 Right Exhaust Temperature Sensor abnormal frequency, pulse width, or period | ||
System Operation
A 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.
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| Illustration 1 | g01380486 |
Schematic of the sensor circuit for the PWM sensors | |
Test Step 1. Verify that the "Exhaust Temperature Sensor Installation Status" Parameter is Programmed Correctly
- Remove electrical power from the ECM.
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector.
- Restore electrical power to the ECM.
- Establish communication with the ECM.
- Verify that the "Exhaust Temperature Sensor Installation Status" parameter is programmed to "Installed".
- Remove electrical power from the ECM.
Expected Result:
The "Exhaust Temperature Sensor Installation Status" parameter is programmed to "Installed".
Results:
- OK - The "Exhaust Temperature Sensor Installation Status" parameter is programmed correctly. Proceed to Test Step 2.
- Not OK - The "Exhaust Temperature Sensor Installation Status" parameter is not programmed correctly.
Repair: Program the "Exhaust Temperature Sensor Installation Status" parameter to "Installed".Verify that the repair eliminates the problem.
STOP
Test Step 2. Inspect the Electrical Connectors and the Wiring
- Thoroughly inspect connectors (1), (2) and (3). Refer to Troubleshooting, "Electrical Connectors - Inspect" for details that are related to inspection of the electrical connectors.
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| Illustration 2 | g01380467 |
Location of the ECM connectors that are for the exhaust temperature sensors (rear engine view) (1) Connector for the left exhaust temperature sensor (2) Connector for the right exhaust temperature sensor (3) J2/P2 ECM connectors | |
- Perform a 45 N (10 lb) pull test on each of the wires in the ECM connector and the customer connector that are associated with the circuit.
 | |
| Illustration 3 | g01380491 |
Terminal locations at the P2 ECM connector that are for the exhaust temperature sensor (P2-14) Digital return (P2-29) Digital sensor supply (P2-65) Left exhaust temperature (P2-39) Right exhaust temperature | |
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| Illustration 4 | g01159881 |
Terminal locations at the connectors for the exhaust temperature sensor (Terminal A) Digital sensor supply (Terminal B) Digital return (Terminal C) Exhaust temperature | |
- Check the allen head screw on each ECM connector for the proper torque. refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- Check the harness and the wiring for abrasion and for pinch points.
Expected Result:
All connectors, pins, and sockets are completely coupled and/or inserted, and the harness and wiring are free of corrosion, of abrasion and of pinch points.
Results:
- OK - The connectors and wiring appear to be OK. Proceed to Test Step 3.
- Not OK - The connectors and/or wiring are not OK.
Repair: Repair the connectors or wiring and/or replace the connectors or wiring.
STOP
Test Step 3. Check the Supply Voltage at the Sensor
- Disconnect the exhaust temperature sensor at the harness connector.
- Restore electrical power to the ECM. Turn the keyswitch to the ON position.
- Measure the voltage across terminal A (digital sensor supply) and terminal B (digital return) on the harness side of the connector.
- Remove electrical power from the ECM. Turn the keyswitch to the OFF position.
- Restore the wiring to the original configuration.
Expected Result:
The supply voltage measures 8.0 ± 0.4 VDC at the sensor connector.
Results:
- OK - The correct supply voltage is measured at the sensor connector. The sensor is receiving the correct supply voltage. Proceed to Test Step 4.
- Not OK - The voltage is not correct at the sensor connector.
Repair: There is a problem in the circuit for the digital sensor supply that is between the ECM and the exhaust temperature sensor. Repair the circuit. Refer to Troubleshooting, "Sensor Supply - Test" for details that are related to troubleshooting a problem with the circuit.
STOP
Test Step 4. Check the Signal Frequency and the Duty Cycle at the Sensor
- Disconnect the sensor connector from the exhaust temperature sensor.
- Remove the signal wire from terminal C of the harness side of the connector for the exhaust temperature sensor.
- Install a 7X-6370 Adapter Cable As (3-PIN BREAKOUT) at the sensor connector.
- Connect the sensor to the breakout harness.
- Restore electrical power to the ECM. Turn the keyswitch to the ON position.
- Measure the frequency and the duty cycle between terminal B (digital return) and terminal C (exhaust temperature) at the 7X-6370 Adapter Cable As (3-PIN BREAKOUT).
- Remove electrical power from the ECM. Turn the keyswitch to the OFF position.
- Remove the breakout harness. Restore the wiring to the original configuration.
Expected Result:
The frequency is between 400 and 600 Hz. The duty cycle is between 22 and 88 percent.
Note: 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.
Results:
- OK - The frequency and the duty cycle are within specifications. The sensor is producing a valid signal. Proceed to Test Step 5.
- Not OK - The frequency and the duty cycle are not within specifications.
Repair: The sensor is not producing a valid signal. Replace the exhaust temperature sensor. Verify that the repair eliminates the problem.
STOP
Test Step 5. Check the Signal Frequency and the Duty Cycle at the ECM
- Remove the signal wire of the suspect sensor from the P2 ECM connector in order to isolate the circuit. The wire will be P2-39 for the right sensor and P2-65 for the left sensor.
- Restore electrical power to the ECM. Turn the keyswitch to the ON position.
- Install a 7X-1709 Multimeter Probe (BLACK) into terminal location P2-14 (digital return) at the ECM connector.
Note: Ensure that the multimeter probe is in good repair. A bent probe may contact other terminals inside the connector.
- Measure the duty cycle and the frequency between the loose wire and the multimeter probe at the ECM connector.
- Remove electrical power from the ECM. Turn the keyswitch to the OFF position.
Expected Result:
The frequency is between 400 and 600 Hz. The duty cycle is between 22 and 88 percent.
Note: 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.
Results:
- OK - The frequency and the duty cycle are within specifications.
Repair: A valid signal appears at the ECM, but the ECM is not detecting the signal properly. There is a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "ECM - Replace" for details.
STOP
- Not OK - The frequency and the duty cycle are not within specifications.
Repair: There is not a valid signal at the ECM connector. Repair the signal wire in the harness that is between the ECM connector and the harness connector for the suspect exhaust temperature sensor. Verify that the repair eliminates the problem.
STOP