Line Pressure Check

Line Pressure Check
The 4HP 16 A/T uses a trochoid type oil pump to produce hydraulic pressure, and a pressure control solenoid (solenoid 1) to control that pressure at the pressure regulator valve, after it leaves the pump. The transaxle pressure control solenoid is controlled by an electrical signal that ranges from 0 - 12 V corresponds to minimum line pressure (approximate. 89.9 - 124.7 psi [6.2 - 8.6 bar]) and 0 V corresponds to a maximum line pressure (approx. 221.9 - 252.4 psi [15.3 - 17.4 bar]) in all range.
Line pressures are calculated for 2 sets of gear ranges - Drive-Park-Neutral and Reverse. This allow the transaxle line pressure to be appropriate for different pressure needs in different gear ranges:





Before performing a line pressure check, verify that the pressure control solenoid is receiving the correct electrical signal from the TCM:
1) Install a scan tool.
2) Start the engine and set parking brake.
3) Check for a stored pressure control solenoid diagnostic trouble code and other diagnostic trouble codes.
4) Repair vehicle, if necessary.





Inspect:
- Fluid level
- Manual linkage
Install or Connect:
- Scan tool (scanner)
- Oil pressure gauge at line pressure port (clutch B or E ports on transaxle case)
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 Solenoid 1 Control Mode on the scanner.
8) Switching solenoid 1 ON/OFF, accelerating the engine to 2,500 rpm, and then read the line pressure at the each gear.
9) Compare data to the Drive-Park-Neutral line pressure chart below.

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

CAUTION: Brake 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 contained in this section.

CAUTION: Clutch damage may occur.

The scanner is only able to control the pressure control solenoid in Park and Neutral with the vehicle stopped.
This protects the clutches from extremely high or low pressures in Drive or Reverse rang.