GUARD AS-TRACK GUIDE 1C9857 - Caterpillar

Possible Causes for an FMI 3 Diagnostic code are:
The power supply circuit for the sensor is open.
The return circuit is open.
The signal circuit is open or the sensor is disconnected.
The signal circuit is shorted to the sensor power supply.
The sensor has failed.
The sensor was activated in Cat ET when the component is not on the machine.
The ECM has failed. This situation is unlikely.Possible Causes for an FMI 4 Diagnostic code are:
The signal circuit for the sensor is shorted to ground.
The sensor has failed.
The ECM has failed. A failure of the ECM is unlikely.
Illustration 1 g03648083
Schematic for the Analog, Active Sensors associated with the Transmission ECM.
Note: The diagram above is a simplified schematic of the Transmission ECM connections. The schematic is electrically correct. However, not all of the possible harness connectors are shown. For the latest version of schematic, refer to: .
Electrical Schematic , UENR1697, "844K Wheel Dozer and 990K Wheel Loader (LRC) Electrical System Schematic" for machines with S/N prefix (S/N: DJK)
Electrical Schematic , UENR4996, "844K Wheel Dozer and 990K Wheel Loader (T4F) Electrical System Schematic" for machines with S/N prefix (S/N: A9P)Diagnostic Trouble Code Procedure
Note: Before performing this procedure, inspect the harness connectors that are involved in the circuit. Poor connections can often be the cause of a problem in an electrical circuit. Verify that all connections in the circuit are clean, secure and in good condition. If a problem with a connection is found, correct the problem and verify that this diagnostic code is active before performing this procedure.
Table 2
Troubleshooting Test Steps Values Results
1. Identify Active DTC Code Associated With Sensor Circuit
A. Use Cat ® ET to confirm all logged diagnostic codes for the machine.
B. Compare the codes to the codes listed in the tables above.
Code present. FMI 3 diagnostic code, proceed to Test Step 2.
FMI 4 diagnostic code, proceed to Test Step 5.
Begin Process For FMI 3 Troubleshooting HERE
2. Check The Supply Voltage at the Sensor
A. Turn key start switch and disconnect switch ON.
B. Disconnect the machine harness from sensor.
C. Refer to the schematic to determine the voltage source for the suspected faulty sensor.
D. Measure voltage between supply and return contacts at the machine harness connector for the sensor.
Voltage is 5 0.3 VDC. OK - The voltage reading is correct for the suspected faulty sensor.
Proceed to Test Step 3.
STOP
NOT OK - The voltage is NOT correct for the circuit.
Repair: If there is an active CID 41, troubleshoot the code. If there is not an active CID 41, replace the circuit breaker associated with the sensor.
3. Check For An Open In The Sensor Circuit
A. The sensor remains disconnected from the machine harness.
B. Turn the key start switch and the disconnect switch OFF.
C. At the harness connector for the sensor, place a jumper wire between the signal contact and frame ground.
D. Disconnect J1 and J2 harness connectors from the ECM.
E. At machine harness connector for ECM, measure the resistance from the signal contact for the sensor to frame ground.
F. Gently pull on the wire and move the