3406E, C12, C15 and C18 Marine Engines Caterpillar

This procedure covers the following diagnostic codes:

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

• 96-04 Fuel Level Sensor short to ground

The fuel level sensor is a component that is installed by the Original Equipment Manufacturer (OEM) 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.

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 1	g01155130
Schematic for the fuel level sensor

Test Step 1. Inspect the Electrical Connectors and the Wiring

1. Turn the keyswitch to the OFF position.

Show/hide table



Illustration 2	g01147202
Left side engine view (typical example) (1) J2/P2 ECM connectors

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

Show/hide table



Illustration 3	g01155286
P2 terminals that are associated with the fuel level sensor (P2-26) Fuel level sensor signal (P2-42) Sensor return

Show/hide table



Illustration 4	g01155187
P803 Fuel level sensor connector (P803-1) Fuel level (P803-2) Sensor return

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

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

5. 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 the Sensor's Resistance at the Sensor

1. Disconnect the J803/P803 connectors.

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

2. Measure the sensor's resistance between P803-1 (fuel level) and P803-2 (sensor return).

Expected Result:

The resistance measurement is between 33 Ohms and 240 Ohms.

Results:

• OK - The resistance of the sensor is between 33 Ohms and 240 Ohms. Record the measurement. Connect the J803/P803 connectors. The sensor's resistance is OK. Proceed to Test Step 3.

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

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

  STOP

Test Step 3. Check the Sensor's Resistance at the ECM

1. Disconnect the J2/P2 connectors.

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

2. Measure the resistance between P2-26 (fuel level sensor) and P2-42 (sensor return) at the ECM connector.

Expected Result:

The resistance measurement is approximately equal to the resistance that was measured at the sensor connector.

Results:

• OK - The resistance measurement is approximately equal to the resistance measurement that was recorded in the previous Test Step.

  Repair: The fuel level sensor and the wiring are OK. Perform the following procedure:

  1. Connect the J1/P1 connectors.

  2. 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.

     2. 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 that was measured at the sensor connector. 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