Input Speed & Output Speed Sensors

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.

Both the Input Speed Sensor (ISS) and the Output Speed Sensor (OSS) are magnetic induction sensors. The input and the output sensors are accessible from the left hand side of the transmission. The ISS is located just forward of center, and the OSS sensor is located near the rear. A voltage signal is induced in the ISS by serrations, which are cut in the outside diameter of the forward clutch housing. Voltage is induced in the output sensor by gear teeth, which are pressed on the outside diameter of the rear carrier assembly.

The PCM uses speed information from these sensors to determine the following:

Whether the engine is running.
Vehicle speed.
Calculation of the gear ratio.
Calculation of TCC slip.
Calculation of turbine speed.

DTC P0502 and P0503 set if a fault exists in the OSS sensor circuit, and the PCM calculates a default value using the ISS values. As long as the fault remains, and the DTC is set, the PCM also commands maximum line pressure, freeze shift adapts, and the MIL illuminates. If the fault is removed, normal operation resumes after the next ignition cycle.