Use this procedure to troubleshoot the electrical system if a problem is suspected with the exhaust temperature sensors or if any one of the diagnostic codes in Table 1 is active or easily repeated.
| 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 1000 Hz or less than 150 Hz.
The ECM detects a duty cycle that is greater than 90 percent or a duty cycle that is less than 10 percent. |
The value of the parameter is set to zero.
The code is logged. |
| 828-8 Right Exhaust Temperature Sensor : Abnormal Frequency, Pulse Width, or Period | The ECM detects a sensor frequency that is greater than 1000 Hz or less than 150 Hz.
The ECM detects a duty cycle that is greater than 90 percent or a duty cycle that is less than 10 percent. |
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System Operation
Both the primary ECM and the secondary ECM can provide digital power and digital sensor reference to the engine sensors. In normal operation, the primary ECM has control of the engine. The primary ECM will provide the digital power and the digital sensor reference to the engine sensors. If the secondary ECM must take over control of the engine, the secondary ECM will provide digital power and the digital sensor reference to the engine sensors.
The power to the engine sensors is switched between the primary ECM and secondary ECM by the relay panel that is mounted on the left side of the engine. When the secondary ECM assumes control of the engine, the sinking driver for the "Backup ECM Active Lamp" is activated. When the sinking driver for the "Backup ECM Active Lamp" is activated, the 8 V power relay in the relay panel is energized. When the 8 V power relay is energized, the digital power to the engine sensors is switched from the primary ECM to the secondary ECM.
The digital sensor reference to the engine sensors is switched between the primary ECM and secondary ECM by the "RSR" relay that is mounted in the control panel. When the secondary ECM assumes control of the engine, the sinking driver for the "Backup ECM Active Lamp" is activated. When the sinking driver for the "Backup ECM Active Lamp" is activated, the "RSR" relay in the control panel is energized. When the "RSR" relay is energized, the digital digital sensor reference to the engine sensors is switched from the primary ECM to the secondary ECM.
The "Pulse Width Modulated (PWM)" sensors provide a signal to the engine's ECM. The sensors receive a 8.0 ± 0.4 VDC regulated voltage from the ECM.
The sensor's wires are routed from the ECM to the sensor connectors. The following list gives the terminal locations for the sensor connector.
- Terminal A 8 V digital sensor supply
- Terminal B Digital sensor reference
- Terminal C Sensor signal
The ECM performs an automatic calibration of these sensors 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.
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| Illustration 1 | g01627272 |
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Typical schematic | |
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| Illustration 2 | g01627273 |
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P1 ECM connector (P1-4) "8 V digital sensor supply" (P1-5) "Digital sensor reference" (P1-11) Left exhaust temperature (P1-12) Right exhaust temperature (P1-55) +Battery (secondary ECM) (P1-57) +Battery (primary ECM) | |
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| Illustration 3 | g01628974 |
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P2 ECM connector (P2-29) "Backup ECM Active Lamp" | |
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| Illustration 4 | g01327759 |
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Terminal locations for the A-C1/E-C2/E-C1 Right hand cross over harness (Terminal C) "8 V digital sensor supply" (Terminal D) "Digital sensor reference" (Terminal R) "Right exhaust temperature" | |
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| Illustration 5 | g01622856 |
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Connector locations (1) A-C1/E-C2/E-C1 Right hand cross over harness (2) A-C2/J-C2/J-C1 Right hand cross over harness (3) A-C90/P-C1 Connectors for the power distribution panel (4) A-C91/P-C2 Connectors for the power distribution panel (5) A-C60 Connector for the prelube motor (6) A-C92/F-C1/F-C2/G-C6 Connectors for a RH Control panel (7) C-C22 Primary ECM connector P2 (8) C-C15 Primary ECM connector P1 (9) C-C28 Secondary ECM connector P2 (10) C-C29 Secondary ECM connector P1 (11) C-C47 Connector for the power relay panel (12) C-C17/F-C1/F-C2/G-C6 Connectors for a LH Control panel (13) C-C18/(TB-C1 customer or L-C1/L-C2 EMCP 3) connectors (14) C-C2/J-C1/J-C2 Left hand cross over harness (15) C-C1/E-C1/E-C2 Left hand cross over harness | |
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| Illustration 6 | g01234146 |
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Location of ECM connectors | |
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| Illustration 7 | g01094844 |
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Sensor connector (Pin A) Sensor supply (Pin B) Sensor return (Pin C) Signal | |
Test Step 1. Check for an "Active" Diagnostic Code
- Turn the ECS to the OFF position.
- Connect Caterpillar Electronic Technician (ET) to the service tool connector.
- Turn the ECS to the STOP position.
- Monitor the diagnostic codes on Cat ET. Check and record any diagnostic codes.
Note: Wait at least 30 seconds in order for the diagnostic codes to become active.
- Determine if a diagnostic code has occurred several times.
Note: A diagnostic code that is logged several times is an indication of an intermittent problem. Most intermittent problems are the result of a bad connection between a socket and a pin in a connector or a bad connection between a wire and a terminal.
- Determine if a 8 diagnostic code is active for one of the exhaust temperature sensors:
Expected Result:
No diagnostic code is active for the exhaust temperature sensors.
Results:
- OK - No diagnostic codes are active.
Repair: If the problem is intermittent, refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct procedures for inspecting electrical connectors.
STOP
- Not OK - A 8 diagnostic code is active or the diagnostic code is logged several times. Proceed to Test Step 2.
Test Step 2. Check the Digital Supply Voltage at the Sensor Connector
- Disconnect the suspect sensor(s) at the sensor connector:
- Measure the voltage on the ECM side of the sensor connector between pin A and pin B for the suspect sensor(s).
Expected Result:
The supply voltage is 8.0 ± 0.4 VDC.
Results:
- OK - The supply voltage is 8.0 ± 0.4 VDC. Proceed to Test Step 3.
- Not OK - The supply voltage is not 8.0 ± 0.4 VDC.
Repair: Refer to Troubleshooting, "Sensor Supply - Test".
STOP
Test Step 3. Check the Digital Sensor's Signal Frequency and the Duty Cycle at the Sensor Connector
- Turn the ECS to the OFF position.
- Remove the sensor's signal wire from pin C of the sensor connector.
- Turn the ECS to the STOP position.
- Measure the frequency and the duty cycle between the sensor's signal wire and pin B of the suspect digital sensor at the sensor connector.
- Turn the ECS to the OFF position.
- Replace the sensor's signal wire and reconnect the sensor.
Expected Result:
The duty cycle is between 10 to 90 percent. The frequency reading is approximately 500 Hz.
Results:
- OK - The frequency and the duty cycle are correct. Proceed to Test Step 4.
- Not OK - The frequency or the duty cycle is not correct.
Repair: Replace the sensor. Verify that no diagnostic codes are active for the suspect sensor before permanently installing the sensor.
STOP
Test Step 4. Check the Sensor's Duty Cycle at the ECM
- Turn the ECS to the OFF position.
- Remove the suspect signal wire for the sensor from ECM connector P1. Refer to Illustration 1 for the terminal locations for the ECM connector.
- Turn the ECS to the STOP position.
- Measure the duty cycle between the sensor's signal wire and the sensor's return wire.
Note: Set the multimeter to "VDC". Press the "Hz" button twice so that the % symbol is displayed.
- Turn the ECS to the OFF position. Reconnect all wires.
Expected Result:
The duty cycle is between 10 to 90 percent.
Results:
- OK - The duty cycle is correct.
Repair: Replace the ECM. Refer to the diagnostic procedure Troubleshooting, "ECM - Replace".
STOP
- Not OK - The duty cycle is not correct.
Repair: There is a problem in the wiring between the ECM and the connector for the sensor. Repair the connectors and/or wiring between the ECM and the connector for the sensor.
STOP