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Home >> GMC >> 1998 >> C3500 HD 7.4 J, Automatic >> Repair and Diagnosis >> External Pages >> Different car >> Section 22 (Transfer Case - Diagnosis - New Venture 246) >> DTC Tests >> DTC C0305: Front Speed Sensor Malfunction >> Circuit Description

Circuit Description

WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 1998 GMC Yukon, 1998 GMC Suburban, 1998 GMC Pickup, 1998 GMC Cab & Chassis, and 1998 Chevrolet Tahoe. However, it is still accessible from the selected car via links, so may be relevant.

Front drive shaft speed sensor is a permanent magnet (PM) generator. Sensor produces a pulsing AC voltage. AC voltage level and number of pulses increases as speed increases. ATC control module converts pulsating AC voltage to drive shaft RPM, which is used for calculations and to monitor differences between front and rear drive shaft speed. It is also used in AUTO mode to determine amount of slip and percent of torque to apply to front axle. Drive shaft RPM can be displayed using scan tool. ATC control module only monitors this signal when vehicle is in AUTO, 4H and 4L positions. DTC C0305 detects an open, short to ground or faulty sensor.