Line Pressure Check Procedure

LINE PRESSURE CHECK PROCEDURE
The HYDRA-MATIC 4T40-E uses a vane type oil pump to produce hydraulic pressure, and a transaxle Pressure Control Solenoid (PCS) to control that pressure at the pressure regulator valve, after it leaves the pump. The transaxle PCS is controlled by an electrical signal that ranges from 0 to 1.1 amp. 1.1 amp corresponds to minimum line pressure (approximately 310 to 380 kPa: 45 - 55 psi [not 0 psi]) and 0 amps corresponds to a maximum line pressure (approximately 965 to 1240 kPa: 140 to 180 psi) in Overdrive (D).





Line pressures are calibrated for two sets of gear ranges - Drive-Park-Neutral and Reverse. This allows the transaxle line pressure to be appropriate for different pressure needs in different gear ranges.
Before performing a line pressure check, verify that the PCS is receiving the correct electrical signal from the Powertrain Control Module (PCM):
1. Install a scan tool.
2. Start the engine and set parking brake.
3. Check for a stored PCS Diagnostic Trouble Code (DTC), and other diagnostic trouble codes.





4. Repair vehicle, if necessary.
Inspect:
- Fluid level.
- Manual linkage.
Install or Connect:
- Scan tool.
- Oil pressure gage at line pressure tap.
5. Put gear selector in Park and set the parking brake.
6. Start engine and allow it to warm up at idle.
7. Access the "PCS Control" test on the scan tool.
8. Increase DESIRED PCS in 0.1 Amp increments and read the corresponding line pressure on the pressure gage. (Allow pressure to stabilize for 5 seconds after each current change.)





9. Compare data to the Drive-Park-Neutral line pressure chart.

Notice: Total test running time should not exceed 2 minutes, or transaxle damage could occur.

CAUTION: Brakes must be applied at all times to prevent unexpected vehicle motion.

If pressure readings differ greatly from the line pressure chart, refer to the Diagnosis Charts. Automatic Transmission/Transaxle
The scan tool is only able to control the PCS in Park and Neutral with the vehicle stopped. This protects the clutches from extremely high or low pressures in Drive or Reverse ranges.

NOTE: Pressures are at 70°C and vary with temperature. Pressure drops as temperature increases.