Line Pressure Test
WARNING: This page is about a different car, the 2018 Ford F-550 Super Duty, 2018 Ford F-450 Super Duty, 2018 Ford F-350 Super Duty, and 2018 Ford F-250 Super Duty. However, it is still accessible from the selected car via links, so may be relevant.
NOTE:
Carry out the Line Pressure Test prior to carrying out the Stall Speed Test . If the line pressure is low at idle, do not carry out the Stall Speed Test or further transmission damage can occur. Do not maintain Wide Open Throttle (WOT) in any transmission range for more than 5 seconds.
This test verifies that the line pressure is within specification.
-
NOTE: The line pressure tap is an M10 X 1.00 thread. Do not use a National Pipe Thread (NPT) fitting when installing a pressure gauge. If a NPT fitting is used, damage to the transmission case will occur.
Connect the Transmission Fluid Pressure Gauge to the line pressure tap using an M10 X 1.00 fitting.
- Start the engine and check the line pressures. Refer to the Line Pressure Chart to determine if the line pressure is above the minimum specification.
- 3. Compare LINEDSD# to actual measured pressure. Actual measured pressure should be within 10 PSI (69 kPa).
Line Pressure Chart - Diesel Engines
| Gear | Line Pressure - kPa (psi) | |
|---|---|---|
| - | Idle | WOT Stall |
| P, N | 619 (90) | - |
| R | 619 (90) | 1, 790 (260) |
| (D) | 619 (90) | 1, 550 (225) |
| 3 | 619 (90) | 1, 100 (160) |
| 2 | 619 (90) | 1, 650 (235) |
| 1 | 619 (90) | 1, 550 (225) |
Line Pressure Chart - Gas Engines
| Gear | Line Pressure - kPa (psi) | |
|---|---|---|
| - | Idle | WOT Stall |
| P, N | 619 (90) | - |
| R | 619 (90) | 1, 675 (240) |
| (D) | 619 (90) | 1, 600 (230) |
| 3 | 619 (90) | 1, 230 (180) |
| 2 | 619 (90) | 1, 675 (240) |
| 1 | 619 (90) | 1, 600 (230) |
Line Pressure Diagnosis Chart
| Test Results | Possible Source |
|---|---|
| HIGH at IDLE - ALL RANGES | Wiring Harnesses (open circuit/high resistance to LPC) LPC solenoid mechanically stuck ON * Verify LPC operation by monitoring LINE pressure while commanding LINEDSD# up and down LPC (main pressure regulator) valve stuck in default position * Raise engine RPM to 2000 RPM * Verify LPC solenoid and LPC valve operation by monitoring LINE pressure while commanding LINEDSD# up and down |
| LOW at IDLE - ALL RANGES | Low Fluid Level LPC solenoid mechanically stuck OFF * Raise engine RPM to 2000 RPM * Verify LPC operation by monitoring LINE pressure while commanding LINEDSD# up and down Fluid Inlet Filter/Seal LPC (main pressure regulator) valve stuck in spring compressed position Broken or missing LPC (main pressure regulator) Valve spring Pump |
| LOW in Park ONLY | Main Control |
| LOW in Reverse ONLY | Separator Plate Low/Reverse (1, R) Clutch Valve Body Direct (3, 5, R) Clutch |
| LOW in Neutral ONLY | Main Control |
| LOW in DRIVE ONLY | Low/Reverse (1, R) Clutch Forward (1, 2, 3, 4) Clutch Main Control |