DTC 74, Transmission Input Speed Sensor Circuit (4L80-E): Notes

Sensor consists of a permanent magnet surrounded by a coil of wire. As forward clutch housing rotates, an AC voltage is induced in circuit. Signal voltage and frequency vary directly with forward clutch rotational speed.

DTC 74 will set when:

DTC 24, 28 or 71 is not set.
Transmission range not in Park or Neutral.
Engine speed greater than 300 RPM.
Transmission output speed greater than 200 RPM.
Transmission input speed less than 50 RPM.
All conditions are met for 2 seconds.

PCM will default to no TCC operation.

NOTE: Test numbers refer to numbers on diagnostic chart.

This checks entire circuit for continuity.
This checks output of the input speed sensor.