Low or contaminated automatic transmission fluid (ATF) from a leak, incorrect fill level, or neglected service; A failing hydraulic pressure unit, including a worn pressure regulator valve or solenoid that cannot hold commanded pressure; A faulty pressure sensor that reports low pressure when the unit is actually working correctly; A clogged transmission filter or restricted fluid pickup that starves the pump; Internal leaks from worn seals, valve body gaskets, or a cracked pressure unit housing; A weak or failing transmission fluid pump that cannot supply the required volume; Wiring or connector faults between the pressure sensor, solenoid, and TCM that corrupt the pressure signal

DTC codes / P09xx · Transmission / P0944

P0944Hydraulic Pressure Unit Loss of Pressure

Q: What does code P0944 mean?

Hydraulic Pressure Unit Loss of Pressure. P0944 means the transmission control module (TCM) has detected that the hydraulic pressure unit is not building or holding the pressure it commands, so the unit has effectively lost pressure. The computer compares commanded pressure against actual pressure from a sensor and sets the code when the two disagree beyond a calibrated threshold.

P0944 means the transmission control module (TCM) has detected that the hydraulic pressure unit is not building or holding the pressure it commands, so the unit has effectively lost pressure. The computer compares commanded pressure against actual pressure from a sensor and sets the code when the two disagree beyond a calibrated threshold.

SystemPowertrain

Code typeGeneric (all makes)

SeverityHigh

Fix difficultyProfessional

AreaTransmission

Symptoms you may notice

Illumination of the transmission or check engine light, often with no other symptoms besides the warning light
Harsh or delayed shifts, especially when engaging drive or reverse from a stop
Transmission slipping under acceleration or failing to hold a gear
Limp-home mode with a single fixed gear or reduced power
Whining or buzzing noise from the transmission area when the pump is starved of fluid
In severe cases, the vehicle refuses to move or loses forward/reverse engagement entirely

Common causes, most likely first

Low or contaminated automatic transmission fluid (ATF) from a leak, incorrect fill level, or neglected service
A failing hydraulic pressure unit, including a worn pressure regulator valve or solenoid that cannot hold commanded pressure
A faulty pressure sensor that reports low pressure when the unit is actually working correctly
A clogged transmission filter or restricted fluid pickup that starves the pump
Internal leaks from worn seals, valve body gaskets, or a cracked pressure unit housing
A weak or failing transmission fluid pump that cannot supply the required volume
Wiring or connector faults between the pressure sensor, solenoid, and TCM that corrupt the pressure signal

How to diagnose and fix it

Check the ATF level and condition first, looking for low level, burnt smell, or metallic debris, and top up or service as needed
Scan all modules for related codes and freeze-frame data to see the commanded versus actual pressure at the moment the code set
Inspect the transmission wiring harness and pressure sensor connector for chafing, corrosion, or loose pins
Test the pressure sensor and pressure control solenoid with a multimeter and, where specified, a pressure gauge at the test port
Replace the transmission filter and fluid if the unit is starved or contaminated, then clear the code and road test
If pressure still drops, remove and inspect the hydraulic pressure unit and valve body for stuck valves, worn bores, or damaged seals
Repair or replace the pressure unit, pump, or internal seals as indicated, then verify with a live pressure reading and a full drive cycle

What P0944 does not always mean

A low fluid level from a slow leak is the most common cause of P0944, and many pressure units are replaced when a simple fluid service and leak repair would have fixed it.
A failing pressure sensor can report low pressure while the hydraulic unit is healthy, so always compare the sensor reading against a mechanical gauge before condemning the unit.
The code can be set by a restricted filter or pickup rather than a failed pump, especially after a neglected service interval or after debris from a previous failure.
Intermittent wiring faults at the pressure sensor connector can mimic a pressure loss and set P0944 without any mechanical problem inside the transmission.
Some vehicles set P0944 as a companion code when another transmission fault forces the unit into a default pressure mode, so diagnose all stored codes before replacing parts.

Can I keep driving with P0944?

Stop driving as soon as it is safe to do so, because continued operation with low hydraulic pressure can destroy clutches and the transmission itself. If the vehicle must be moved, keep it to a short distance at low speed and avoid heavy acceleration or towing.

Tools that help

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Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.