794 AC Off-Highway Truck VIMSTM 3G and Truck Payload Measurement System (TPMS) Caterpillar

Sensor Supply - Test

Usage:

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Illustration 1	g03597477
Sensor circuit

Use this procedure to troubleshoot the electrical system if a sensor supply circuit problem is suspected.

Sensor supply voltage is routed from the ECM to terminal A of each sensor connector. The sensor return is routed from the ECM to terminal B 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 FMI 3 diagnostic codes are active, a sensor may have been damaged. Check for any active sensor diagnostic codes to determine if a sensor has failed.

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Illustration 2	g03401543
Sensor connector terminals (A) Terminal A, sensor supply (B) Terminal B, sensor return (C) Terminal C, sensor signal

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Table 1
Troubleshooting Steps	Expected Results	Results
1. Check for An Active Diagnostic Code A. Connect Cat^® Electronic Technician (Cat ET) to the service tool connector. B. Turn on the battery disconnect switch and the key start switch. C. Monitor Cat ET for codes.⁽¹⁾	There is no active code	OK - There is no active code. STOP Not OK - There is an active code. Go to Step 2.
2. Check Connectors A. Inspect the circuit harness connectors.	Connectors are: * Clean * Secure * In good condition	OK - Connectors are OK. Go to Step 3. Not OK - Connectors are not OK. Repair: A. Correct any connection problem. B. Verify that the problem is corrected. STOP
3. Check the Supply Voltage at the Sensor Connector A. Turn off the battery disconnect switch. B. Disconnect the harness connectors of the suspect sensor. C. Turn on the battery disconnect switch and the key start switch. D. Measure the voltage between terminals A and B at the sensor connector.⁽²⁾	Voltage is correct⁽³⁾	OK - The voltage is correct. Repair: A. Replace the sensor. B. Verify that the problem is corrected. STOP NOT OK - The voltage is not correct. Go to Step 4.
4. Check the Supply Voltages at the ECM A. Turn off the battery disconnect switch. B. Disconnect the J1 and J2 ECM connectors. C. Turn on the battery disconnect switch and the key start switch. D. Measure the voltage of the sensor supply pin of the ECM.	Voltage is correct⁽³⁾	OK - The voltage is correct. Contact your Technical Communicator.⁽⁴⁾ STOP NOT OK - The voltage is not correct. The supply wire is shorted or open. Repair: A. Repair the supply wire. B. Verify that the problem is corrected. STOP

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⁽¹⁾	Wait at least 30 seconds for the diagnostic codes to become active.
⁽²⁾	Wiggle the harness to reveal an intermittent condition.
⁽³⁾	See the machine Electrical Schematic to determine system voltage.
⁽⁴⁾	If ECM replacement is required, see Troubleshooting, "Electronic Control Module (ECM) - Replace ".