Line Pressure Check

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:
- The engine must be OFF.
- The vehicle must be level with the parking brake engaged.
- Ensure that the automatic transmission fluid level is correct.
- Remove the closure bolt on the left side of the torque converter housing and connect the Fluid Pressure Gauge J-21867.
- Install the scan tool.
- Allow the engine to idle at the normal operating temperature.

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.