EDGE-CUTTING 4T2974 - Caterpillar

Illustration 1 g03788765The sensor signal for the passive sensor is routed from the ECM to terminal 1 of the sensor connector. The sensor return for the passive sensors is routed from the ECM to terminal 2 of the sensor connector.The ECM continuously creates a pull-up voltage on the signal wire for each sensor. The ECM uses this pull-up voltage in order to detect a problem in the signal circuit. When the ECM detects voltage that is above a threshold on the signal wire, the ECM activates a high voltage -3 diagnostic code. When the ECM detects voltage that is below a threshold on the signal wire, the ECM activates a low voltage -4 diagnostic code.Note: There may be a delay of 30 seconds or more in order for Cat® Electronic Technician (ET) to display an active diagnostic code. When you check for a diagnostic code, be sure to wait at least 30 seconds.
Illustration 2 g01218763
Terminal locations at the sensor connector for the analog sensors
(Terminal 1) Sensor signal
(Terminal 2) Analog return
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 -3 code is active.
Proceed to Test Step 2.
Result: A -4 code is active.
Proceed to Test Step 3.
Result: For a code that is logged, but not currently active.
Proceed to Test Step 4.
2. Create a Short at the Sensor Connector
A. Turn the main disconnect switch to the OFF position.
B. Disconnect the sensor with the active -3 code.
C. Install the jumper wire between the following terminals at the sensor connector:
- Terminal 1 (sensor signal) and Terminal 2 (sensor return)
D. Connect Cat ET.
E. Use Cat ET to monitor the following:
- -4 code
F. Turn the main disconnect switch to the OFF position.
Create a Short
Result: The -3 code remains active.
Repair: There is an open in the wiring harness. Repair or replace the wiring harness.
Verify that the repair eliminated the problem.
Result: A -4 code became active.
Repair: The wiring harness is OK. Replace the sensor.
Verify that the repair eliminated the problem.
3. Create an Open at the Sensor Connector
A. Turn the main disconnect switch to the OFF position.
B. Disconnect the sensor with the active -4 code.
C. Connect Cat ET.
D. Use Cat ET to monitor the following:
- -3 code
Note: For a 110-3 code, start the engine and let the engine idle for 7 minutes. The engine must be running for at least 7 minutes in order for the diagnostic to run.
E. Turn the main disconnect switch to the OFF position.
Create an Open
Result: The -4 code remains active.
Repair: There is an open in the wiring harness. Repair or replace the wiring harness.
Verify that the repair eliminated the problem.
Result: A -3 code became active.
Repair: The wiring harness is OK. Replace the sensor.
Verify that the repair eliminated the problem.
4. Perform the Wiggle Test
Carefully following this procedure is the best way to identify the root cause of an intermittent problem.
A. Connect Cat ET.
B. Use CAT ET to perform the following test:
- "Wiggle Test"
C. Slowly wiggle the wiring