Automatic Transmission Input Shaft Speed, Output Shaft Speed Sensors

WARNING: This page is about a different car, the 2003 GMC Yukon XL, 2003 Chevrolet Suburban, and 2003 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.

Fig 1: Identifying Automatic Transmission Input Shaft Speed Sensor

Courtesy of GENERAL MOTORS CORP.

Both of the automatic transmission input shaft speed (AT ISS) and the automatic transmission output shaft speed (AT OSS) sensors are magnetic induction sensors. The input and the output sensors are accessible from the left hand side of the transmission. The AT ISS sensor is located just forward of center and the AT OSS sensor is located near the rear. A voltage signal is induced in the AT ISS sensor 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.

Fig 2: Identifying Automatic Transmission Output Shaft Speed Sensors

Courtesy of GENERAL MOTORS CORP.

The PCM used speed information from these sensors in order to determine the following:

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

Code P0502 and P0503 set if a fault exists in the AT OSS sensor circuit, and the PCM calculates a default value using the AT ISS sensor values. As long as the fault remains, and the code 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.