K 1500 Suburban 4WD V8-5.3L VIN Z Flex Fuel (2003)
Transmission Speed Sensor: Description and Operation
4L80-E/4L85-E
Automatic Transmission Input Shaft Speed, Output Shaft Speed Sensors / 4L80-E/4L85-E
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.
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.
