K 3500 Truck 4WD V8-5.7L VIN R (1998)
Transmission Speed Sensor: Description and Operation
4L80-E Automatic Transmission
AUTOMATIC TRANSMISSION INPUT(SHAFT) SPEED, OUTPUT(SHAFT) SPEED SENSORS
Both of the Automatic Transmission Input(Shaft) Speed (A/T ISS) and the Automatic Transmission Output(Shaft) Speed (A/T OSS) Sensors are
magnetic induction sensors. The input and the output sensors are accessible from the left hand side of the transmission. The A/T ISS Sensor is located
just forward of center and the A/T OSS Sensor is located near the rear. A voltage signal is induced in the A/T 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 VCM/PCM used speed information from these sensors in order to determine the following:
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Whether the engine is running
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Vehicle speed
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Calculation of the gear ratio
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Calculation of TCC slip
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Calculation of turbine speed
Type D code(s) P0502 (VCM) or P0722, P0723 (PCM) will set if a fault exists in the A/T OSS Sensor circuit, and the VCM/PCM will calculate a
default value using the A/T ISS Sensor values. As long as the fault remains and the code is set, the VCM/PCM will also command maximum line
pressure, freeze shift adapts, and the MIL will illuminate. If the fault is removed, normal operation will resume after the next ignition cycle.
For diesel engines, type B fault codes P0723 and P0724 will set.
