Perform this test before a hoist or road test in order to make sure that electronic control inputs are connected and operating. If you do not check the inputs before operating the transmission, you could misdiagnose a simple electrical condition as a major transmission condition.

The PCM provides valuable information. Use the PCM on the Hydra-Matic 4T80-E transmission for accurate diagnosis.

1. Move the gear selector to Park (P) and set the parking brake.
2. Install the scan tool.
3. Start the engine.
4. Proceed to the PCM Data.
5. Verify that the following signals are present on the scan tool:

•	Throttle Position Signal (TPS)

•	Battery voltage (Battery)

•	Engine speed (RPM)

•	Vehicle speed (MILES/HOUR)

•	Automatic Transmission Fluid Pressure Manual Valve Position switch state (TFP Switch)

•	Input speed (TURBINE)

•	Slip speed (SLIP SPEED)

•	Actual Transmission Pressure Control Solenoid Amperage (ACT CURRENT)

•

RATIO

•	Transmission Fluid Temperature (Trans Temp)

•	TCC duty cycle (TCC DC)

•	Engine Coolant Temperature (ECT)

6. Monitor the Automatic Transmission Fluid Pressure Manual Valve Position Switch (TFP Switch) signal by moving the gear selector through all of the ranges. Verify that the TFP Switch state matches the various combinations for the gear states selected. Refer to the Circuit Combination table at the end of this list. If the combinations (ON, ON, ON) or (ON, OFF, ON) are displayed, a condition may exist with the TFP Switch and its related connectors. Gear selections should be immediate and not harsh.
7. Move the gear selector to Neutral and monitor the Throttle Position Signal (TPS) while increasing and decreasing engine RPM with the accelerator pedal. The throttle angle should increase with the engine RPM.
8. Monitor the TCC BRAKE signal while tapping the brake pedal with your foot. The brake switch signal should be:

Released -- when the brake pedal is released

Applied -- when the brake pedal is depressed