For a complete wiring diagram Refer to Section 8W.The fuel level rationality will set a fault for a fuel level reading that does not change over an accumulated mileage threshold to keep stuck high or stuck low fuel levels from disabling OBD monitors. If the vehicle is fitted with a saddle tank fuel system this feature includes diagnostics for both of the sending units and diagnostics for a siphon tube that has become disconnected or plugged. The power up test looks to see a large enough fuel level voltage change from the last key-off to the following engine run. The engine run test looks to see a fuel level voltage change over an accumulated mileage. When Monitored:TEST No.1: With the ignition on, the fuel level is compared to the previous key down after a 20 second delay. TEST No.2: The PCM monitors the fuel level at ignition on.Set Condition:TEST No.1: If the PCM does not see a difference in fuel level of greater than 0.1 volt the test will fail. TEST No.2: If the PCM does not see a change in the fuel level of .1765 over a set amount of miles the test will fail. Two trip fault. Three good trips to turn off the MIL.Possible Causes(N4) FUEL LEVEL SIGNAL CIRCUIT OPEN(N4) FUEL LEVEL SIGNAL CIRCUIT SHORTED TO GROUND(K900) SENSOR GROUND CIRCUIT OPENFUEL TANKFUEL LEVEL SENSORAlways perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).1. ACTIVE DTCDiagnose any CAN - C or CAN - B Communication DTCs before continuing.Diagnose P0462 or P0463 first, if set along with P0461.Start the engine.Allow the engine to reach normal operating temperature.With a scan tool, select View DTCs and record the related Freeze Frame data.It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.Is the DTC Active or Pending at this time?YesGo To 2NoRefer to the INTERMITTENT CONDITION Diagnostic Procedure.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 2. VISUALLY INSPECT FUEL TANKVisually inspect the Fuel Tank for damage that may restrict the Fuel Sending Unit float from moving.Is the Fuel Tank OK?YesGo To 3NoReplace the Fuel Tank as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) 3. (N4) FUEL LEVEL SIGNAL CIRCUIT OPEN

Turn the ignition off.Disconnect the Fuel Pump Module harness connector.Disconnect the C7 TIPM harness connector.Measure the resistance of the (N4) Fuel Level Signal circuit from the Fuel Pump Module harness connector to the TIPM harness connector.Is the resistance below 5.0 ohms?YesGo To 4NoRepair the open in the (N4) Fuel Level Signal circuit.Perform BODY VERIFICATION TEST-VER 1. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES - STANDARD PROCEDURE)4. (N4) FUEL LEVEL SIGNAL CIRCUIT SHORTED TO GROUND

Measure the resistance between ground and the (N4) Fuel Level Signal circuit in the Fuel Pump Module harness connector.Is the resistance below 100 ohms?YesRepair the short to ground in the (N4) Fuel Level Signal circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 55. (K900) SENSOR GROUND CIRCUIT OPEN

Disconnect the C2 PCM harness connector.Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.Measure the resistance of the (K900) Sensor Ground circuit from the Fuel Pump Module harness connector to the appropriate terminal of special tool #8815.Is the resistance below 100 ohms?YesRepair the open in the (K900) Sensor Ground circuit.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 66. INTERNAL INSPECTION OF THE FUEL TANKThe fuel system is under a constant pressure (even with the engine off). Before testing or servicing any fuel system hose, fitting or line, the fuel system pressure must be released. Failure to follow these instructions can result in personal injury or death.Remove the Fuel Tank per Service Information.Remove the Fuel Pump Module.Visually inspect the inside of the Fuel Tank for any obstructions or deformities.Inspect the Fuel Pump Module Float arm for damage.Were any problems found?YesRepair or replace as necessary.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE) NoGo To 7 7. FUEL LEVEL SENSORIf there are no possible causes remaining, view repair.RepairReplace the Fuel Level Sensor.Perform the POWERTRAIN VERIFICATION TEST. (Refer to 9 - ENGINE - STANDARD PROCEDURE)