Flexible Fuel Sensor: Description and Operation

FLEXIBLE FUEL SENSOR

SPECIAL SERVICE MESSAGE EFFECTIVE DATE: 10/03/2002
Oasis #16275 2000 TAURUS AND 2001 TAURUS/SABLE FLEXIBLE FUEL VEHICLES 0460

SOME 2000 TAURUS AND 2001 TAURUS/SABLE FLEXIBLE FUEL VEHICLES MAY EXHIBIT A DIFFICULT TO DIAGNOSE ERRATIC FUEL GAUGE. THIS CONDITION MAY ALSO ILLUMINATE A MALFUNCTION INDICATOR LAMP (MIL), WITH A DIAGNOSTIC TROUBLE CODE (DTC) P0460 STORED IN THE PCM'S MEMORY. THIS MAY BE CAUSED BY THE FLEXIBLE FUEL SENSOR MODULE (LOCATED UNDER THE DRIVER SIDE DASHBOARD BEHIND THE RADIO). IF NORMAL DIAGNOSIS DOES NOT PINPOINT THE CAUSE, REPLACE THE FLEXIBLE FUEL SENSOR MODULE (BASE PART #14A069). EFFECTIVE DATE: 10/03/2002

Flexible Fuel (FF) Sensor:

The Flexible Fuel (FF) sensor (Figure 30) is a capacitive device that detects the dielectric constant, conductivity and temperature of the fuel being fed to the engine. From this information, the FF sensor generates a duty cycle frequency that it supplies to the PCM telling it the percentage of ethanol in the fuel.

In general, as the percentage of ethanol in the fuel mixture increases, the output frequency of the FF sensor signal increases. The relationship between ethanol alcohol percentage and duty cycle frequency is as follows:

Frequency Table:

All duty cycle frequency values are +1/-5%. It is important to note that currently no fuel with greater than 85% ethanol alcohol content is being produced. The PCM uses the percent ethanol information to calculate the correct A/F (air/fuel) ratio and spark advance for the vehicle.

Beginning in the 2001 model year, not all vehicles are equipped with flexible fuel sensors. On vehicles without flexible fuel sensors, the PCM calculates the A/F ratio based upon Heated Oxygen Sensor (HO2S) input signals.