Line Pressure Check

HYDRA-MATIC 4L80-E LINE PRESSURE CHECK PROCEDURE







Line pressures are calibrated for two sets of gear ranges-Drive-Park-Neutral, and Reverse. This allows the transmission line pressure to be appropriate for different pressure needs in different gear ranges:

Drive, Park, or Neutral: 35-171 psi
Reverse: 67-324 psi

Before performing a line pressure check, verify that the pressure control solenoid for the transmission is receiving the correct electrical signal from the vehicle computer:
1. Install a scan tool

NOTICE: The transmission may experience harsh, soft or mushy shifts for up to two days later.

CAUTION: Keep the brakes applied at all times in order to prevent unexpected vehicle motion.

2. Start the engine and set the parking brake
3. Check for diagnostic trouble codes, including the diagnostic code for a stored pressure control solenoid.
4. Repair the vehicle if necessary. Include the following areas:
- Inspect the fluid level.
- Inspect the manual linkage at the transmission.
- Install or connect the TECH 1 scan tool.
- Install or connect the oil pressure gage at the line pressure tap.
5. Put the gear selector in Park and set the parking brake.
6. Start the engine and allow the engine to warm up at idle.
7. Access the Override Pressure Control Solenoid test on the TECH 1 scan tool.
8. Increase the Pressure Control Solenoid Current in 0.1-amp increments. Read the corresponding line pressure on the pressure gage. Allow the pressure to stabilize for 5 seconds after each current charge.
9. Compare your data to the Drive-Park-Neutral Line Pressure.

Line pressure will pulse either high or low every ten seconds in order to keep the pressure control solenoid plunger free. This is a normal condition and will not harm the transmission.

Line Pressure Specifications:

If your pressure readings differ greatly from the line pressure chart, refer to the Diagnosis Charts. The TECH 1 scan tool is only able to control the pressure control solenoid in Park and Neutral with the vehicle stopped at idle. This protects the clutches from extremely high or low pressures in Drive or Reverse ranges.