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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 62 (Automatic Transmission Diagnosis - 4L80-E) >> Diagnostic Tests >> DTC P0502: VSS Circuit - Low Input >> Circuit Description

Circuit Description

WARNING: This page is about a different car, the 2002 GMC Yukon XL, 2002 GMC Sierra, 2002 Chevrolet Suburban, and 2002 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The OSS sensor, which is a permanent magnet generator, provides the vehicle speed information to the PCM. The permanent magnet generator produces a pulsing AC voltage as the transmission speed sensors rotor teeth pass through the sensor's magnetic field. The AC voltage level and the number of pulses increase as the speed of the vehicle increases. The PCM then converts the pulsing voltage to a digital signal for vehicle speed. The vehicle speed is used for engine and transmission calculations.

If the PCM detects a low vehicle speed and there is a high engine speed in a drive gear range, DTC P0502 sets. For California emissions and vehicles under 8600 GVW, DTC P0502 is a type "B" DTC. For all other vehicles, DTC P0502 is a type "C" DTC.

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