BOLT 0960551 - Caterpillar

System OperationThe Electronic Control Module (ECM) supplies a regulated voltage of 5.0 0.2 VDC to the sensors.The supply voltage for the sensors is routed from the ECM to terminal 1 of each sensor connector. The sensor return for the sensors is routed from the ECM to terminal 2 of each sensor connector. The ECM provides short circuit protection for the internal power supply. A short circuit to the battery will not damage the internal power supply.Note: The sensors are not protected from overvoltage. A short from the supply line to the +Battery may damage the sensors. If any of the diagnostic codes are active, a sensor may have been damaged. Repair the sensor supply and check for any active sensor diagnostic codes in order to determine if a sensor has been damaged.
Illustration 1 g01240891
Sensor connector
(1) 5 V or 8 V sensor supply
(2) Sensor return
(3) Signal
Table 2
Sensor Supply Sensor Supply ECM Location
Sensor Supply #1 Sensors on the engine ECM J2 connector
Sensor Supply #2 Sensors on the engine ECM J1 connector
Illustration 2 g03450476
Typical schematic
The signal wires are not shown in Illustration 2.
Note: The diagram above is a simplified schematic of the ECM - relay circuit. The schematic is electrically correct. However, not all of the possible sensors or harness connectors are shown. Refer to the latest revision of the Electrical Schematic for the complete schematic for your application.
Table 3
Troubleshooting Test Steps Values Results
1. Determine the Code
A. Connect Cat ET to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools", if necessary.
B. Turn the keyswitch to the ON position.
C. Determine if a diagnostic trouble code is present.
Diagnostic Codes
Result: A -3 or -4 code is present.
Note which ECM is reporting the active sensor supply code.
Proceed to Test Step 2.
Result: A -21 code is present.
Proceed to Test Step 3.
2. Check for a Failed Sensor
A. Connect to Cat ET.
B. Turn the keyswitch to the ON position.
C. Disconnect a sensor on the suspect sensor supply circuit.
D. Monitor Cat ET while the sensor is disconnected to see if the active code changes to logged.
E. Connect the suspect sensor to the wiring harness
F. Repeat steps C through E for each sensor on the suspect sensor supply.
Failed Sensor
Result: The suspect sensor supply active code changes to logged when a sensor is unplugged.
Repair: Replace the failed sensor.
Verify that the repair resolved the problem.
Result: The suspect sensor supply active code remains active after all sensors on the sensor supply circuit have been checked.
Repair: A failed wiring harness has been detected. Repair or replace the wiring harness.
Verify that the repair resolved the problem.
3. Check the Sensor Supply
A. Turn the keyswitch to the OFF position.
B. Unplug the suspect sensor from the wiring harness.
C. Place a jumper wire between pin 1 and pin 2 on the suspect sensor wiring harness connector.
D. Connect to Cat ET.
E. Turn the keyswitch to the ON position.
F. Monitor the diagnostic codes using Cat ET.
Diagnostic Codes
Result: A -4 code is activated on the suspect sensor supply.
Repair: Remove the sensor. Check the sensor passage for a blockage or obstruction. Also,