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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1068 (Engine Controls Diagnosis - 4.8L, 5.3L, & 6.0L (DTCS P0141 To P0446)) >> Diagnosis >> DTC P0179 >> Circuit Description

Circuit Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

Alcohol content and fuel temperature information is supplied to the powertrain control module (PCM) from the fuel composition sensor (FCS). The FCS has the following circuits:

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 and 150 hertz. The normal pulse width ranges between 1 and 5 milliseconds. The microprocessor inside the sensor is capable of a certain amount of self-diagnosis. An output frequency of 170 hertz indicates that the fuel is contaminated or an internal sensor fault has been detected. If the PCM detects a signal more than 155 hertz, DTC P0179 will set.

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