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 (approx. 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 - 7.4 bar]) in all range.

Line pressures are calculated for two 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).
     Fig 1: Checking Transaxle Line Pressure

     Courtesy of SUZUKI OF AMERICA CORP.
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.

If pressure readings differ greatly from the line pressure chart, refer to the PRESSURES CHART .

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 range.