P0461

Diagnostic Chart 1 Of 2:

Diagnostic Chart 2 Of 2:

Fuel Level Sensor Inspection:

Schematic:

CIRCUIT DESCRIPTION
The Powertrain Control Module (PCM) uses input from the fuel level sensor to calculate expected vapor pressures within the fuel system. Vapor pressures vary as the fuel level changes. Vapor pressure is critical to determining if the EVAP control system is operating properly. Fuel level information is used in determining whether to run an EVAP control system diagnostic. A fuel level that is too high or too low may prevent the EVAP control system diagnostics from accurately detecting a fault.

CONDITIONS FOR RUNNING THE DTC
The engine is running.

CONDITIONS FOR SETTING THE DTC
The change in fuel level from maximum to minimum is less than 1 gallon even though the volume of intake air is calculated to be more than 660 kg.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active.
^ The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

CONDITIONS FOR CLEARING THE MIL/DTC
^ The MIL turns OFF after three consecutive trips during which the diagnostic runs and no fault is detected.
^ A History DTC will clear after 40 consecutive warm-up cycles without a fault.
^ DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed.

DIAGNOSTIC AIDS
Check for any of the following conditions:
^ If a DTC P0463 is also displayed, diagnose that DTC first.
^ A stuck fuel level sensor may cause a DTC P0461 to set.
^ A loose fuel tank baffle may interfere with the movement of the fuel level sensor float.
^ A corroded or loose fuel level sensor chassis ground-Operate the tail lamps and brake lamps while checking the fuel level sensor reading on a scan tool. Increasing the current flow through the G400 chassis ground can reveal a faulty circuit connection.
^ A faulty electrical connection at the PCM.

Check the resistance of the fuel level sensor at the positions:

An open in the fuel level sensor circuit will indicate a 0 percent fuel level (empty fuel tank), while a short to ground in the fuel level sensor circuit will indicate a 100 percent fuel level (full fuel tank).

An intermittent malfunction may be caused by a fault in the fuel level sensor electrical circuit. Inspect the wiring harness and components for any of the following conditions:
^ Backed out terminals
^ Improper mating of terminals
^ Broken electrical connector locks
^ Improperly formed or damaged terminals
^ Faulty terminal to wire connections
^ Physical damage to the wiring harness
^ A broken wire inside the insulation
^ Corrosion of electrical connections, splices, or terminals

If the DTC P0461 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

TEST DESCRIPTION
The numbers below refer to the step numbers in the diagnostic table.
1. The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the applicable Freeze Frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information for later reference.
5. This step checks the circuit from the fuel level sensor to the PCM. The scan tool will display a default value of 100 percent all the time if a DTC for a fuel level sensor circuit is present. Current DTCs or saved DTCs for a fuel level sensor circuit must be cleared before reading the fuel level parameter.
6. This step checks for a faulty fuel level sensor.