Loss of Flex Fuel Calibration Signal

WHEN MONITORED
With the ignition ON.

SET CONDITION
The flex fuel sensor calibration signal is not between 4.63 and 4.28 volts for a 1.5 second period after key is on for two consecutive key ON cycles.

THEORY OF OPERATION
The flex fuel sensor provides an analog voltage proportional to the concentration of methanol in the fuel mixture to the PCM.

- The flex fuel sensor voltage signal varies between 0.5 volts, for 0 % methanol, and 4.5 volts for 85 % methanol.

- Maximum recommended concentration of methanol is 85 %.

- The sensor also has a calibration voltage of 4.5 volts for 2 seconds upon power up or key on.

A microprocessor inside the flex fuel sensor calculates the concentration of methanol in the fuel using input from an electrical sensing element and 2 temperature sensors, and generates a corresponding output voltage.

- The electrical sensing element measures the portion of an electric charge that is passed though the fuel mixture. The amount of charge passed through the mixture depends on the concentration of methanol in the fuel mixture.

- Fuel temperature sensor immersed in fuel.

- Circuit board temperature sensor mounted on sensor circuit board.

PROBABLE CAUSES
- Open 8-volt supply circuit
- Flex fuel sensor failure
- PCM failure