A proper line pressure is essential for a proper transmission operation. Carry out the following fluid pressure check after checking the automatic transmission fluid level:

Perform this test during the hoist or road test. It is easier to check pressures during the hoist test because the tubing and the pressure gauge can remain outside of the vehicle and will not incur damage by any road conditions or debris. The technician can diagnose the problem more quickly on the hoist since the driver does not have to watch the road.

The Hydra-Matic 4L30-E uses a vane type oil pump in order to produce the hydraulic pressure, and a transmission pressure control solenoid in order to control that pressure at the pressure regulator valve after the hydraulic pressure leaves the pump. The TCM controls the transmission pressure control solenoid.

1. Depress the brake pedal firmly. Increase the engine speed until a stall is attained. Run the transmission in the various modes (economy/sport/winter programs) and selector lever positions, as specified in the following table.

Important: The engine runs under the stipulated conditions at a specific stall speed (above 1500 RPM, normally approximately 2200 RPM). Under these conditions, the transmission fluid heats very rapidly; therefore, each individual test step must not last more than 5 seconds. If necessary, allow the transmission to cool down between each test. Put the selector lever in Neutral and allow the engine to idle for approximately 1 minute in order to cool the transmission down. Use the scan tool in order to monitor the transmission fluid temperature. Under the normal conditions, the transmission fluid temperature is in the range from 70°C to 120°C/ 158°F to 248°F.

2. Compare the scan tool value for the pressure control solenoid current consumption and the transmission fluid pressure from the pressure gauge with the relevant values in the Mode vs Pressure at Stall Speed Table below.
3. Once the check is completed, remove the Fluid Pressure Gauge J 21867, insert the closure bolt and tighten to 14 N·m (10 lb ft).
4. If the specified pressure checks are not successfully completed, check the following transmission components for faults:

4.1.	The transmission fluid pump

4.2.	The pressure control solenoid valve

4.3.	The transmission fluid filter

4.4.	The fluid screen of pressure regulator

4.5.	The pressure limiting valve

4.6.	The throttle valve switch damaged

4.7.	The connection ducts between the above components