The fuel level sensor is a component that is installed by the customer. The sensor is a passive sensor. The sensor does not require an operating voltage from the Electronic Control Module (ECM).
Use this procedure to troubleshoot the electrical system if a problem is suspected with the fuel level sensor or if any one of the diagnostic codes in Table 1 is active or easily repeated.
| Diagnostic Codes Table | ||
|---|---|---|
| Code and Description | Conditions which Generate this Code | System Response |
| 96-3 Fuel Level Sensor voltage above normal | The voltage on the signal wire for the fuel level sensor is above normal. | The code is logged. |
| 96-4 Fuel Level Sensor voltage below normal | The voltage on the signal wire for the fuel level sensor is below normal. | |
When the fuel tank is full, the fuel level sensor has a resistance of 33 Ohms. When the fuel tank is empty, the fuel level sensor has a resistance of 240 Ohms. The resistance from the fuel level sensor varies between these values as the fuel level varies.
The sensor's variable resistance affects the pull-up voltage that is created by the ECM. When the sensor's resistance is low, the pull-up voltage is low. When the sensor's resistance is high, the pull-up voltage is high. Refer to Table 2.
| Relationship Between the Sensor's Resistance and the Voltage on the Signal Wire | ||
|---|---|---|
| Fuel Level | Resistance | Approximate Voltage on the Signal Wire |
| Full | 33 Ohms | 0.15 VDC |
| Empty | 240 Ohms | 1.8 VDC |
The most likely electrical problem with the circuit for the fuel level sensor is a problem in the wiring harness. The next likely cause is a problem with the fuel level sensor. The least likely cause is a problem with the ECM.
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| Illustration 1 | g01372172 |
|
Schematic of the circuit that is for the fuel level sensor | |
Test Step 1. Verify that the "Fuel Level Sensor Installation Status" Parameter is Programmed Correctly
- Remove electrical power from the ECM.
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector.
- Restore electrical power to the ECM.
- Establish communication with the ECM.
- Verify that the "Fuel Level Sensor Installation Status" parameter is programmed to "Installed".
- Remove electrical power from the ECM.
Expected Result:
The "Fuel Level Sensor Installation Status" parameter is programmed to "Installed".
Results:
- OK - The "Fuel Level Sensor Installation Status" parameter is programmed correctly. Proceed to Test Step 2.
- Not OK - The "Fuel Level Sensor Installation Status" parameter is programmed to "Not Installed".
Repair: Program the "Fuel Level Sensor Installation Status" parameter to "Installed".
Verify that the repair eliminates the problem.
STOP
Test Step 2. Inspect the Electrical Connectors and the Wiring
- Remove the electrical power from the ECM.
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Illustration 2 g01176458 Location of the ECM connectors that are for the fuel level sensor (typical left side engine view)
(1) J2/P2 ECM connectorsShow/hide table
Illustration 3 g01372185 Location of the sensor connectors that are for the fuel level sensor (typical rear engine view)
(2) Connector for the fuel level sensor - Thoroughly inspect connectors (1) and (2). Refer to Troubleshooting, "Electrical Connectors-Inspect" for details.
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Illustration 4 g01372194 Terminal locations at the P2 ECM connectors that are associated with the fuel level sensor
(P2-38) Fuel level
(P2-93) ReturnShow/hide table
Illustration 5 g01155187 Terminal locations at the harness connector for the fuel level sensor
(1) Fuel level
(2) Sensor return - Perform a
45 N (10 lb) pull test on each of the wires that are associated with the fuel level sensor. - Check the allen head screw on each of the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.
- Check the harness and the wiring for abrasion and for pinch points from the fuel level sensor to the ECM.
Expected Result:
All connectors, pins and sockets are completely coupled and/or inserted and the harness and wiring are free of corrosion, of abrasion and of pinch points.
Results:
- OK - The connectors and the wiring are OK. Proceed to Test Step 3.
- Not OK - There is a problem in the connectors and/or the wiring.
Repair: Repair the connectors and/or the wiring. Replace parts, if necessary. Verify that the repair eliminates the problem.
STOP
Test Step 3. Check the Resistance of the Sensor at the Harness Connector
- Disconnect the fuel level sensor at the harness connectors.
- Measure the sensor's resistance between terminal 1 (fuel level) and terminal 2 (sensor return) at the harness connector. Record the measurement.
Expected Result:
The resistance measurement of the sensor is between 33 and 240 Ohms.
Results:
- OK - The resistance measurement is between 33 and 240 Ohms. Connect the harness connectors that are for the fuel level sensor. The sensor's resistance is OK. Proceed to Test Step 4.
- Not OK - The resistance measurement of the sensor is not between 33 and 240 Ohms.
Repair: The sensor's resistance is not within the specifications that are necessary for the ECM to interpret the signal. Verify that the fuel level sensor is operating correctly. Refer to the literature that is provided by the OEM for the sensor. Adjust the sensor's resistance, when possible. Replace the sensor, if necessary.
STOP
Test Step 4. Check the Resistance of the Sensor Through the Harness
- Remove the wire from terminal location P2-38 for the fuel level sensor from the ECM connector in order to isolate the circuit.
- Install a 7X-1709 Multimeter Probe (BLACK) into terminal location P2-93 (sensor return) at the ECM connector.
Note: Ensure that the multimeter probe is in good repair. A bent probe may contact other terminals inside the connector.
- Measure the resistance between the loose wire and the multimeter probe at the ECM connector. Record the measurement.
Note: Be sure to wiggle the harness during the measurement in order to reveal an intermittent electrical condition in the harness.
Expected Result:
The resistance measurement of the sensor through the harness is between 33 and 240 Ohms.
Results:
- OK - The resistance measurement is between 33 and 240 Ohms.
Repair: The sensor's resistance is OK and the vessel's wiring is OK. The sensor's resistance and the resistance through the wiring harness is OK. There appears to be a problem with the ECM. Replace the ECM. Refer to Troubleshooting, "ECM - Replace" for details.
STOP
- Not OK - The resistance measurement of the sensor through the harness is not between 33 and 240 Ohms.
Repair: The resistance of the sensor at the sensor connector is within specifications. The resistance of the sensor through the harness is not within specifications. There is a problem in the wiring harness that is between the ECM connector and the sensor connector. There may be a problem with a connector. Repair the wiring, when possible. Replace parts, if necessary. Verify that the problem is resolved.
STOP