Description

Fuel Level Sensor Description

1. Fault Codes:
Fuel level sensor fault: (P1199 for pre 1997MY vehicles)
Fuel level rationality fault: P0461

2. Monitoring Procedure

Range Check
The resistance of the fuel level sensor changes in relation to the level of fuel in the tank. Through connection to the input resistor networks of the ECM; any disconnection of the sensor at different points in the harness can generate both high and low input voltages, which are outside the normal operating voltage range. These are detected to diagnose a fuel level fault in the system.

If the value of Fuel Level Volts is less than Fuel Level Diag Min Volts or more than Fuel Level Diag Max Volts, then an appropriate fault counter is incremented up to a limit of fuel level diagnostic fault limit. Otherwise the fault counter is decremented down to a limit of zero. If the fault counter reaches the limit then a fuel level sensor fault is present.

Rationality Check
The rationality test on the fuel tank level sensor consists of monitoring the fuel level sensor output and ensuring that the output value changes during a period of time. This test will check that the sensor float is not stuck or holed. The test can be passed either through fuel slosh or a drop in level due to fuel usage. To ensure that the test can be completed even where the vehicle is being used for successive short journeys, the test parameters are stored at power down and retrieved at the next power up.

3. Primary Detection Parameter
Fuel level - Measured in volts, the outcome of a potential divider calculation.

4. Fault Criteria Limits
Fuel Level - Low out of range 0.49V
Fuel Level - High 4.8V
Fuel Level change must be less than 2 (dec) for a period of time greater than 59 minutes

5. Monitoring Conditions
The range test will take place only when the engine is running.
The rationality test will take place when the vehicle speed is greater than 50 mph.

6. Monitoring Time Length / Frequency of Checks
The frequency of the fuel level diagnostic is 2Hz.

7. Criteria for Storing Fault Code
Two successive trips where the fuel level diagnostic indicates a failed fuel level sensor.

8. Criteria for Illuminating MIL
Two successive trips where the fuel level diagnostic indicates a failed fuel level sensor.

9. Criteria for Determining Out of Range Input Signals
The fuel level sensor is subject to the range test above.