P0944: Hydraulic Pressure Unit Loss of Pressure

What it means

TCM detects rapid loss of hydraulic pressure in transmission accumulator or main pump circuit.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

The transmission accumulator and main pump circuit help store and maintain hydraulic pressure for shifts, and the TCM monitors whether that pressure holds. P0944 sets when pressure falls rapidly, indicating that the accumulator or pump circuit may not retain pressure.

Common causes

Most likely first.

1. Accumulator leak
2. Pump seal failed

Symptoms

• Check engine or transmission warning light on
• Harsh, delayed, or missing shifts
• Possible limp mode (locked in one gear)
• Slipping or shuddering during gear changes

How to diagnose it

1. Save freeze-frame data and review available pressure readings to see when the pressure drop occurs.
2. Check fluid level and condition using the vehicle's specified procedure, and look for external leaks around the transmission and pump.
3. Scan for related pump, pressure, or shift codes that could help identify when pressure is being lost.
4. Inspect accessible pump and accumulator connections for damage or fluid leakage.
5. Test pressure retention in the accumulator and main pump circuit against the manufacturer's specification to confirm internal leakage or a failed seal.

Common fixes

• Correct the fluid level and repair any external leak.
• Repair damaged connections or seals at the pump or accumulator.
• Replace a leaking accumulator if testing confirms it cannot retain pressure.
• Repair the pump circuit or replace a failed pump seal as indicated by pressure testing.

Can I keep driving?

Do not continue driving if shifts slip, engagement is delayed, or drive drops out; rapid pressure loss can make the transmission unreliable and worsen damage. Have the vehicle recovered if it cannot shift predictably.