P0461

Diagnostic Chart:

Schematic:

CIRCUIT DESCRIPTION
The VCM requires an accurate indication of fuel level for EVAP system diagnosis. The fuel level in the fuel tank changes the rate of vacuum decay for the EVAP system leak DTCs.

The fuel level sensor changes resistance based on fuel level. The fuel level sensor has a signal circuit and a ground circuit. The VCM applies a voltage of about 5 volts on the signal circuit to the sensor. The VCM 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 VCMs signal voltage is only pulled down a small amount through the sensor to ground.

Therefore, the VCM will sense a high signal voltage (fuel tank full). When the fuel tank is empty, the sensor resistance is low, and the signal voltage is pulled down a greater amount. This causes the VCM to sense a low signal voltage (fuel tank empty).

The VCM uses the input from the fuel level sensor to calculate the fuel level in the fuel tank. This information is then sent to the Instrument Panel Cluster (IPC) through the serial data line.

The diagnostic will not run when the tank is more than 85 percent or less than 15 percent full. (This sensor signal disables the misfire when the fuel levels are less than 15 percent).

CONDITIONS FOR RUNNING THE DTC
The VCM has confirmed that the fuel tank is between 15 percent and 85 percent full.

CONDITIONS FOR SETTING THE DTC
The VCM does not detect a decrease in fuel level over a distance of 200 miles (320 Km).

ACTION TAKEN WHEN THE DTC SETS
^ The control module stores the DTC in history after the first failure but will not illuminate the Malfunction Indicator Lamp (MIL).
^ The control module records the operating conditions at the time the diagnostic fails. The control module stores the failure information in the scan tools Freeze Frame/Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles.
^ A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during the same ignition cycle.
^ Use the scan tool Clear Information function.

DIAGNOSTIC AIDS

IMPORTANT: Fuel level is used to determine EVAP system diagnosis. Always diagnose the fuel level sensor before any other EVAP system components or DTCs.

Do not use the fuel gauge as an indication of a shorted or open circuit as the IPC may always default to EMPTY or FULL depending upon the vehicle model.

Check for the following conditions:

^ A faulty connection or a damaged harness. Inspect VCM harness connectors for the following:
- Backed out terminals
- Improper mating
- Broken locks
- Faulty wire to terminal connections
^ Test for an intermittent condition. Monitor a scan tool or digital voltmeter connected between the related circuits while moving the connectors and harnesses. If the failure is induced, the voltage reading will change. This will help locate a circuit problem.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
2. This step determines if there is a wiring problem.
3. This step determines if the fuel level sensor signal and ground circuits are OK.