C32 Marine Engines Fuel Level Sensor Circuit - Test Caterpillar


Fuel Level Sensor Circuit - Test
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C32 Marine Engines [RENR9303]
ELECTRICAL AND STARTING SYSTEM
SENSOR GP

System Operation Description:

The fuel level sensor is an OEM installed component for the vessel. The sensor is a passive sensor. The sensor does not require an operating voltage from the Electronic Control Module (ECM).

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 1.

Table 1
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    

If the voltage on the signal wire falls below 0.15 VDC, a 96-04 diagnostic code is activated. If the voltage on the signal wire rises above 1.8 VDC, a 96-03 diagnostic code is activated. There is an eight second delay before either code is activated.

A diagnostic code is probably caused by a problem in a wiring harness. The next likely cause is a problem with the fuel level sensor. The least likely cause is a problem with the ECM.




Illustration 1g01129074

Schematic for the fuel level sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

  1. Turn the keyswitch to the OFF position.



    Illustration 2g01130312

    Engine components for the fuel level sensor

    (1) J1/P1 ECM connectors

    (2) J803/P803 connectors for the fuel level sensor

  1. Thoroughly inspect connectors (1) and (2). Refer to Troubleshooting, "Electrical Connectors-Inspect" for details.



    Illustration 3g01130327

    P1 terminals that are associated with the fuel level sensor

    (P1-3) Return

    (P1-15) Signal




    Illustration 4g01120369

    Harness connector for the fuel level sensor

    (1) Signal

    (2) Return

  1. Perform a 45 N (10 lb) pull test on each of the wires that are associated with the fuel level sensor.

  1. Check the allen head screw on the ECM connectors for the proper torque. Refer to Troubleshooting, "Electrical Connectors - Inspect" for the correct torque values.

  1. 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 2.

  • 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 2. Check for Active Diagnostic Codes

  1. Connect the AVSpare Electronic Technician (ET) to the service tool connector. Refer to Troubleshooting, "Electronic Service Tools".

  1. Turn the keyswitch to the ON position.

  1. Observe the "Active Diagnostic" screen on Cat ET. Wait at least 15 seconds so that any codes may become active. Look for these codes:

    • 96-03 Fuel Level Sensor open/short to +batt

    • 96-04 Fuel Level Sensor short to ground

Expected Result:

One of the above codes is active.

Results:

  • Active 03 code - An 03 diagnostic code is active. Proceed to Test Step 3.

  • Active 04 code - An 04 diagnostic code is active. Proceed to Test Step 4.

  • No active codes - None of the above codes are active.

    Repair: The problem was probably caused by a poor electrical connection. Return the engine to service.

    STOP

Test Step 3. Check the Sensor and the Vessel's Wiring

  1. Disconnect the J803/P803 connectors.

    Note: Be sure to wiggle the harness during the following measurement in order to reveal an intermittent condition.

  1. Measure the sensor's resistance between J803-1 (Signal) and J803-2 (Return).

Expected Result:

The resistance measurement is less than 240 Ohms.

Results:

  • OK - The resistance measurement is less than 240 Ohms. Record the measurement. Connect the J803/P803 connectors. The sensor's resistance is OK and the vessel's wiring is OK. Proceed to Test Step 5.

  • Not OK - The resistance measurement is greater than 240 Ohms.

    Repair: Perform the following procedure:

    1. Disconnect the fuel level sensor from the vessel's wiring. Verify that the fuel level sensor is operating correctly. Refer to the literature that is provided by the OEM for the sensor.

    1. If the sensor is causing the high resistance, adjust the sensor, when possible. Replace the sensor, if necessary. STOP.

    1. If the sensor's resistance reading is correct, there is excessive resistance in the vessel's wiring between the fuel level sensor and the J803/P803 connectors. Repair the wiring. Verify that the problem is resolved.

    STOP

Test Step 4. Check the Sensor and the Vessel's Wiring

  1. Disconnect the J803/P803 connectors.

    Note: Be sure to wiggle the harness during the following measurement in order to reveal an intermittent condition.

  1. Measure the sensor's resistance between J803-1 (Signal) and J803-2 (Return).

Expected Result:

The resistance measurement is greater than 33 Ohms.

Results:

  • OK - The resistance measurement is greater than 33 Ohms. Record the measurement. Connect the J803/P803 connectors. The sensor's resistance is OK and the vessel's wiring is OK. STOP

  • Not OK - The resistance measurement is less than 33 Ohms.

    Repair: Perform the following procedure:

    1. Disconnect the fuel level sensor from the vessel's wiring. Verify that the fuel level sensor is operating correctly. Refer to the literature that is provided by the OEM for the sensor.

    1. If the sensor is causing the low resistance, adjust the sensor, when possible. Replace the sensor, if necessary. STOP.

    1. If the sensor's resistance reading is correct, there is a short circuit in the vessel's wiring between the fuel level sensor and the J803/P803 connectors. Repair the wiring. Verify that the problem is resolved.

    STOP

Test Step 5. Check the Sensor's Resistance at the ECM

  1. Disconnect the J1/P1 connectors.

    Note: Be sure to wiggle the harness during the following measurement in order to reveal an intermittent condition.

  1. Measure the resistance between P1-3 (Return) and P1-15 (Signal).

Expected Result:

The resistance measurement is approximately equal to the resistance measurement from the previous Test Step.

Results:

  • OK - The resistance measurement is approximately equal to the resistance measurement from the previous Test Step. The fuel level sensor and the wiring are OK.

    Repair: Perform the following procedure:

    1. Connect the J1/P1 connectors.

    1. Turn the keyswitch to the ON position. Check for a diagnostic code for the fuel level sensor again.

      1. If the diagnostic code does not recur, the problem is resolved. The original problem was probably caused by a poor electrical connection. Return the engine to service. STOP.

      1. If the diagnostic code recurs, Replace the ECM. Refer to Troubleshooting, "Replacing the ECM". Verify that the problem is resolved.

    STOP

  • Not OK - The resistance measurement is not approximately equal to the resistance measurement from the previous Test Step. There is a problem with the engine's wiring harness. There may be a problem with a connector.

    Repair: Repair the wiring, when possible. Replace parts, if necessary. Verify that the problem is resolved.

    STOP

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