AUTOMATIC TRANSMISSION – GM 5L40-E DESCRIPTION AND OPERATION The output shaft speed is monitored by the EAT ECU and compared to engine speed signals received from the ECM on the CAN. These two signals allow the EAT ECU to calculate the transmission slip ratio for plausibility and maintain adaptive pressure control. Both speed sensors are identical and are located in the main casing and secured with a screw. One sensor is mounted at the front of the transmission and monitors input shaft speed from a toothed target wheel located on the rear of the reverse clutch drum. The second sensor is located at the rear of the transmission and is fitted with a spacer. This sensor monitors the output shaft speed from the teeth on the ring gear of the planetary gearset. The speed sensors are of the inductive type and are connected to the EAT ECU by two wires. The sensor receives a DC supply current from the EAT ECU on one of the wires. As the teeth of the target wheel pass the sensor tip, a change in the magnetic field of the sensor occurs and results in an AC pulse being generated in the sensor field winding. This pulse is passed on the second wire and detected by the EAT ECU which processes the signal to calculate the rotational speed. The AC pulse is proportional to the transmission speed and the EAT ECU measures the peak to peak outputs of the AC waveform to calculate the rotational speed being measured. The resistance of the coil winding is between 324 and 486 Ω at CF. Failure of a speed sensor will cause the EAT ECU to store a related fault code.