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| Illustration 1 | g01338641 |
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Connections of the transmission pressure sensor | |
This diagnostic code is associated with the transmission pressure sensor. The FMI 4 means that the ECM has determined that the voltage of the circuit for the position sensor is below normal. The sensor monitors the hydraulic charge pressure.
The output of the sensor is an analog signal from 0.2 DCV to 4.95 DCV. The voltage changes as the pressure changes. The ECM recognizes a voltage in the range of 0.2 DCV to 4.95 DCV as valid input from the sensor. If the voltage is above 4.95 DCV for more than two seconds, the ECM determines that the sensor is shorted to the + battery.
The possible causes of this diagnostic code are listed below:
- The signal circuit for the sensor is shorted to ground.
- The sensor has failed.
- The ECM has failed. This is unlikely.
Note: The following test procedure may create other diagnostic codes. Ignore these created diagnostic codes and clear the diagnostic codes when the original diagnostic code has been corrected. Ensure that the diagnostic code of SPN 127 FMI 4 is active before performing this procedure.
Note: Use a digital multimeter for the measurements in this procedure.
Test Step 1. CHECK THE SENSOR.
- Turn the disconnect switch and the key start switch to the ON position.
- Ensure that the diagnostic code is active.
- Observe the status of the diagnostic code. Disconnect the sensor from the machine harness.
Expected Result:
The SPN 127 FMI 4 remains active. The FMI has not changed and the 4 is still active.
Results:
- OK - The diagnostic code remains active. The sensor is correct. Proceed to Test Step 2.
- NOT OK - The diagnostic code is no longer active. The sensor has failed.
Repair: Replace the sensor.
STOP
Test Step 2. CHECK THE WIRING HARNESS OF THE SENSOR FOR A SHORT TO GROUND.
- Turn the key start switch and the disconnect switch to the OFF position.
- Disconnect the machine harness from the sensor.
- Disconnect the machine harness connector(s) from the ECM.
- At the machine harness connector for the ECM, measure the resistance from the signal contact J1-51 of the machine harness to all possible sources of ground. Measure the resistance to all contacts of the machine harness connectors for the ECM.
Expected Result:
Each resistance measurement is greater than 5000 ohms.
Results:
- OK - Each resistance measurement is greater than 5000 ohms. The machine harness is correct. Proceed to Test Step 3.
- NOT OK - One or more resistance measurements is not correct. There is a short in the machine harness.
Repair: The short is between signal contact J1-51 and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.
STOP
Test Step 3. CHECK IF THE DIAGNOSTIC CODE IS STILL ACTIVE.
- Inspect the harness connectors. Clean the contacts of the harness connectors and check the wires for damage to the insulation that is caused by excessive heat, battery acid, or chafing.
- Perform a
45 N (10 lb) pull test on each of the wires that are associated with the circuit. - Reconnect all harness connectors in order to make sure that the connectors are fully seated. Also, make sure that the clips for each connector are completely fastened.
- Turn the disconnect switch and the key start switch to the ON position.
- Operate the machine.
- Determine if the diagnostic code is active.
Expected Result:
The diagnostic code is active.
Results:
- YES - The diagnostic code is active. The diagnostic code has not been corrected.
Repair: Check the circuit again. It is unlikely that the ECM has failed. Exit this procedure and perform this procedure again. Prior to replacing an ECM, always contact your dealership for possible consultation with Caterpillar. This consultation may greatly reduce repair time. If the ECM requires replacing, refer to Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
STOP
- NO - The diagnostic code is not active. The diagnostic code does not exist at this time. The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation.
STOP