P0463

Circuit Description
The left Fuel Level sensor, mounted in the rear side of the left fuel tank, measures fuel level changes within the left fuel tank. The left Fuel Level Sensor changes resistance based on fuel level. The Fuel Level Sensor has a signal circuit and a ground circuit. The PCM applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The PCM monitors changes in this voltage caused by changes in the resistance of the sensor to determine fuel level.
When the fuel tank is full, the sensor resistance is high, and the PCM senses high signal voltage. When the fuel tank is empty, the sensor resistance is low, and the PCM senses a low signal voltage.
The PCM uses inputs from the Fuel Level Sensor to calculate the total fuel remaining in the fuel tank(s). This information is then sent to the fuel gauge via the class 2 circuit.
When the PCM senses a signal voltage lower than the normal operating range of the sensor, this DTC sets.
The following is a description on how the fuel pump/system functions: An electric high pressure fuel pump attaches to the fuel sender assembly inside the left fuel tank. The in-tank fuel pump supplies pressurized fuel through an in pipe fuel filter/pressure regulator assembly to the fuel rail. The fuel pressure supplied by the in-tank fuel pump exceeds the fuel injectors required pressure. The pressure regulator, which is part of the fuel filter assembly, regulates the fuel pressure supplied to the fuel injectors. Excess fuel returns from the fuel filter/pressure regulator, through a separate fuel return pipe, to the left fuel tank. The fuel pump delivers a constant flow of fuel to the engine even during low fuel conditions and aggressive vehicle maneuvers. The PCM controls the electric fuel pump operation through a fuel pump relay.
The left tank fuel pump also supplies a small amount of pressurized fuel to the right fuel tank siphon jet pump through the fuel feed rear crossover pipe. The pressurized fuel creates a venturi action inside the siphon jet pump. The venturi action causes the fuel to be drawn out of the right fuel tank. Fuel is then transferred from the right fuel tank to the left fuel tank through the fuel sender fuel feed pipe. The fuel system is designed to maintain a greater level in the left fuel tank then in the right fuel tank when the electric fuel pump is operating. The fuel transfer rate from the left fuel tank to the right fuel tank is less than the transfer rate from the right fuel tank to the left fuel tank. Therefore, with the electric fuel pump operating, the left fuel tank level should be higher than the right fuel tank level.
The fuel level in the fuel tanks equalize when the following occur:
^ The electric fuel pump is not operating.
^ The fuel level is greater than 50 percent.

Conditions for Running the DTC
Engine Running

Conditions for Setting the DTC
^ Fuel Level Sensor voltage is above 2.9 volts
^ The above Conditions are present for 2.0 minutes.

Action Taken When the DTC Sets
^ The PCM stores the DTC information into memory when the diagnostic runs and fails.
^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
^ The fuel gauge displays empty.
^ The Driver Information Center (DIC) displays a message.
^ The Check Gauge lamp illuminates.

Conditions for Clearing the MIL/DTC
^ A History DTC will clear after forty consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
^ A last test failed (Current DTC) will clear when the diagnostic runs and does not fail.
^ Use a scan tool in order to clear the MIL/DTC.

Diagnostic Aids

Important:
^ Remove any debris from the PCM/TAC module connector surfaces before servicing the PCM/TAC module. Inspect the PCM/TAC module connector gaskets when diagnosing/replacing the modules. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM/TAC modules.
^ For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter kit J 35616-A. Using this kit prevents damage to the harness/component terminals.
^ The following may cause an intermittent:
- Poor connections
- Mis-routed harness.
- Rubbed through wire insulation.
- Broken wire inside the insulation.
^ Depending on the current fuel level, it may be difficult to locate a malfunctioning sending unit. The malfunction may only occur when the fuel level is full or near empty. The fuel sending unit may need to be removed for further diagnosis. A Fuel Level sensor that has an intermittent condition causes this DTC to set. Remove the Fuel Level sensor in order to test the resistance of the sensor. The resistance of the sensor should change from 40 to 250 ohms as the float arm is moved from the empty to full positions. Replace the sensor if the resistance did not change or is out of range.
^ The following occurs with this DTC set:
- The vehicle fuel gauge displays empty.
- The Check Gauge lamp illuminates.
- The Driver Information Center displays a message.
^ The voltages in the Fuel Level Conversion Table are approximate values. Use this table to aid in diagnosis.
^ Using Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid determining how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This isolates when the DTC failed. For an intermittent, refer to Symptoms. Symptom Related Diagnostic Procedures

Test Description
The numbers below refer to the step numbers on the Diagnostic Table.
2. If DTC P1635 and P1639 sets at the same time, this indicates that the signal circuit is shorted to a voltage.
3. This step determines if the fault is present.

4. The fuel level sensor may only fail in a certain range. If you determine the condition is intermittent, inquire with the customer when the concern occurred. The concern may only happen when the vehicle is re-fueled or when the fuel level is close to empty. Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This isolates when the DTC failed.
5. If the voltage goes low, this determines the circuits and the PCM are OK.
16. Inspect for poor connections at the PCM harness before replacing the PCM.