How did the shop detemine it was the sensor?What testing did they do?You have to use a scan tool and monitor the FCS. You have to test the circuit for a short to voltage, short to ground or an open. If the circuit tests good and you replaced the FCS then the next step in the diagnostic is to replace the PCM. The fuel composition sensor is controlled by the pcm. For a shop to tell you the sensor goes bad 9 out of 10 times is a pretty poor diagnoses. Plus getting this from a junk yard is a bad idea, its called a junk yard for a reason. The older E-85 vehicles that used E-85 were not as good as the ones today, if you run gasoline in these older e-85 vehicles and then switch to e-85 is contaminates the sensor and fuel sys with corrosion, by getting this sensor from the junk yard you dont know how long it was sitting and if they ran gas or e-85. This is how the fcs works. Alcohol content and fuel temperature information is supplied to the powertrain control module (PCM) from the fuel composition sensor (FCS). The FCS has an ignition 1 circuit, a signal circuit, and a ground circuit. The FCS uses a microprocessor inside the sensor to measure the ethanol percentage and fuel temperature, and changes output signals accordingly. The signal circuit carries both the ethanol percentage, and the fuel temperature within the same signal. The signal is both variable frequency and variable pulse width. The frequency signal indicates the ethanol percentage, and the pulse width indicates fuel temperature. The PCM provides an internal pull up to 5 volts on the signal circuit, and the FCS pulls the 5 volts to ground in pulses. The normal range of operating frequency is between 50-150 Hz. The normal pulse width ranges between 1-5 milliseconds. If the PCM detects a signal less than 45 Hz DTC P0178 will set. Post back with any other questions.
Tuesday, March 10th, 2009 AT 8:54 PM