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.

Use the scan tool on the Hydra-Matic 4T40-E transmission for valuable information and accurate diagnosis.

1. Move the gear selector to Park (P) and set the parking brake.
2. Connect a scan tool to the DLC terminal.
3. Start the engine.
4. Connect power to the scan tool.
5. Verify that the following signals are present on the scan tool:

•	Engine speed (RPM)

•	Transmission input speed (Turbine)

•	Transmission output speed

•	Vehicle speed (miles/hour)

•	A/B/C Range

•	PRNDL select

•	Desired PCS

•	Actual PCS

•	PCS duty cycle

•	Brake switch

•	Engine coolant temperature (Coolant)

•	Transmission fluid temperature (Trans Temp)

•	Throttle angle (TPS)

•	System volts

6. Monitor the BRAKE SWITCH 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

7. Monitor the PRNDL SELECT signal and move the gear selector through all the ranges.

Verify that the PRNDL SELECT value matches the gear range indicated on the instrument panel or console.

The gear selections should be immediate and not harsh.

8. Move the gear selector to Neutral and monitor the throttle angle signal while increasing and decreasing engine RPM with the accelerator pedal.

The throttle angle should increase with engine RPM.