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 passive sensor. The fuel level sensor does not require an operating voltage in order to provide a signal. This configuration utilizes a fuel level buffer that helps to reduce the amount of indicator movement that is passed to the fuel gauge. The buffer is powered through a circuit that is wired directly to a circuit breaker.
When the fuel tank is full, the fuel level sensor has a resistance of 0 to 3.5 Ohms. When the fuel tank is empty, the fuel level sensor has a resistance of 92 to 98 Ohms. The resistance from the fuel level sensor varies between these values as the fuel level varies.
An active diagnostic code for the fuel level sensor is probably caused by 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 Electronic Control Module (ECM).
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| Illustration 1 | g01176463 |
Schematic for the fuel level sensor | |
Test Step 1. Inspect Electrical Connectors and Wiring
- Turn the keyswitch to the OFF position.
- Thoroughly inspect the J1/P1 ECM connectors. Refer to Troubleshooting, "Electrical Connectors-Inspect" for details.
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| Illustration 2 | g01141049 |
J1/P1 ECM connectors (left side engine view) | |
- Perform a 45 N (10 lb) pull test on each of the wires that are associated with the fuel level sensor.
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| Illustration 3 | g01176464 |
P1 terminals that are associated with the fuel level sensor (P1-5) Fuel level sensor signal (P1-68) Sensor return | |
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| Illustration 4 | g01155187 |
P803 Fuel level sensor connector (P803-1) Fuel level (P803-2) Sensor return | |
- Check the allen head screw on 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 appear to be OK. Proceed to Test Step 2.
- Not OK - There is a problem in the connectors and/or the wiring.
Repair: Repair the circuit. Verify that the repair eliminates the problem.
STOP
Test Step 2. Confirm the Fuel Level in the Tank
- Visually check the fuel level in the tank.
- Compare the fuel level in the tank to the indicator on the fuel level sender.
Expected Result:
The fuel level in the tank agrees with the indicator on the fuel level sender.
Results:
- OK - Proceed to Test Step 3.
- Not OK - The indicator on the fuel level sender does not reflect the actual fuel level in the tank.
Repair: Replace the fuel level sender. Verify that the repair eliminates the problem.
STOP
Test Step 3. Check the Status of the Fuel Level
- Turn the keyswitch to the OFF position.
- Connect the Caterpillar Electronic Technician (ET) to the service tool connector.
- Turn the keyswitch to the ON position.
- Observe the status of "Fuel Gauge" on Cat ET.
Note: The "Fuel Gauge" on Cat ET represents the percentage of fuel level in the tank.
- Turn the keyswitch to the OFF position.
Expected Result:
The status of "Fuel Gauge" displays the correct fuel level.
Results:
- OK - Cat ET displays the correct fuel level.
Repair: The fuel level sensor appears to be operating correctly at this time. There may be an intermittent problem in the harness or in a connector. Refer to Troubleshooting, "Electrical Connectors - Inspect" if the problem is intermittent.
STOP
- Not OK - Cat ET does not display the correct fuel level. Proceed to Test Step 4.
Test Step 4. Check the Resistance of the Fuel Level Sender
- Disconnect the fuel level sender from the fuel level buffer.
- Measure the resistance between the terminals on the receptacle for the fuel level sender.
The correct resistance is between 0 and 3.5 Ohms when the indicator is on "F". The correct resistanceis between 92 and 98 Ohms when the indicator is on "E".
- Reconnect the fuel level sender.
Expected Result:
The resistance is less than 98 Ohms.
Results:
- OK - The resistance is less than 98 Ohms. The fuel level sender appears to be OK. Proceed to Test Step 5.
- Not OK - The resistance is out of the range.
Repair: Replace the fuel level sender. Verify that the repair eliminates the problem.
STOP
Test Step 5. Check the Supply Voltage to the Buffer
- Disconnect the connector at the fuel level buffer.
- Turn the keyswitch to the ON position.
- Measure the voltage across terminal A (+Battery) and terminal B (digital return) at the breakout.
Expected Result:
The supply voltage is approximately 24 VDC.
Results:
- OK - Battery voltage is present at the connector for the fuel level buffer. The buffer is receiving the correct supply voltage. Proceed to Test Step 6.
- Not OK - The buffer is not receiving the correct supply voltage.
Repair: Check the machine's circuit breaker panel for a tripped circuit breaker. Verify that the ground circuit has continuity. Repair any problems that are found with the circuit. Verify that the repair eliminates the problem.
STOP
Test Step 6. Check the Isolated Signal Frequency and the Duty Cycle
- Install a 7X-6370 Adapter Cable As (3-PIN BREAKOUT) at the connector for the fuel level buffer.
- Remove the signal wire from the harness side of the connector for the fuel level buffer. Leave the breakout in place.
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| Illustration 5 | g01159881 |
(A) +24 V Supply (B) Digital Return (C) Signal | |
- Turn the keyswitch to the ON position.
- Measure the frequency and the duty cycle between terminal B (digital return) and terminal C (signal) at the breakout.
- Turn the keyswitch to the OFF position.
- Reinstall the signal wire in the connector and remove the breakout. Leave the connector disconnected.
Expected Result:
The frequency is between 5 and 6.5 kHz. The duty cycle is between 20 and 95 percent.
Results:
- OK - The frequency and the duty cycle are correct. The buffer is producing a valid signal. Proceed to Test Step 7.
- Not OK - The frequency and the duty cycle are not correct.
Repair: The buffer is not producing a valid signal. Replace the fuel level buffer. Verify that the repair eliminates the problem.
STOP
Test Step 7. Check the Harness for a Short Circuit
- Ensure that the keyswitch is in the OFF position and that the fuel level buffer is disconnected from the harness.
- Disconnect the J1/P1 ECM connectors.
- Measure the resistance between P1-5 (digital return) and P1-68 (fuel level sensor).
- Leave the connector disconnected.
Expected Result:
The measurement indicates an open circuit.
Results:
- OK - The measurement indicates that an open circuit exists. The harness is not shorted. Proceed to Test Step 8.
- Not OK - The measurement does not indicate that an open circuit exists. There is a short in the harness.
Repair: Repair the harness. Verify that the repair eliminates the problem.
STOP
Test Step 8. Check for an Open Circuit in the Harness
- Fabricate a jumper wire that is long enough to jumper two terminals at the ECM connector. Crimp connector pins to each end of the jumper wire.
- Install the jumper wire between P1-5 (digital return) and P1-68 (fuel level).
- Measure the resistance at the connector for the fuel level buffer between terminal B (digital return) and terminal C (signal).
- Remove the jumper wire and reconnect the fuel level buffer.
Expected Result:
The resistance of the harness is less than 5 Ohms.
Results:
- OK - The measurement is correct. The wiring in the harness is not open. Proceed to Test Step 9.
- Not OK - The resistance of the harness wiring is greater than 5 Ohms.
Repair: There is an open circuit in the harness wiring. Repair the harness or replace the harness. Verify that the repair eliminates the problem.
STOP
Test Step 9. Check the Signal Frequency and the Duty Cycle at the ECM
- Install a 140-2266 Cable As (70-PIN BREAKOUT) between the J1/P1 ECM connectors.
- Ensure that the connectors for the fuel level buffer are connected.
- Turn the keyswitch to the ON position.
- Measure the frequency and the duty cycle at the breakouts between P1-5 (digital return) and P1-68 (fuel level sensor).
- Turn the keyswitch to the OFF position.
Expected Result:
The frequency is between 5 and 6.5 kHz. The duty cycle is between 20 and 95 percent.
Results:
- OK - The signal is reaching the ECM.
Repair: A valid signal is reaching the ECM, but the ECM is not reading the signal properly. Replace the ECM. Refer to Troubleshooting, "Replacing the ECM". Verify that the repair eliminates the problem.
STOP
- Not OK - The frequency and the duty cycle are not correct at the ECM.
Repair: There appears to be an intermittent problem in the wiring harness or in the connectors. Isolate the problem and make the necessary repairs. Refer to Troubleshooting, "Electrical Connectors - Inspect" for details in finding intermittent problems with the connectors. Verify that the repair eliminates the problem.
STOP