P0942: Hydraulic Pressure Unit

What it means

The TCM detects a generic fault in the hydraulic pressure unit. Pump output, pressure regulation, or accumulator function impaired.

At a glance

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

How it works

The hydraulic pressure unit supplies and regulates the pressure used to operate the transmission, with the TCM monitoring whether the unit can provide expected operation. P0942 sets when the TCM detects a general pressure-unit fault, which may involve weak pump output, regulation, or accumulator function.

Common causes

Most likely first.

1. Hydraulic pump worn
2. Internal leakage

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 check transmission fluid condition and level using the vehicle's specified procedure, since low or degraded fluid can impair pressure generation.
2. Scan for related transmission codes and review available pressure or pump data to see whether the fault points to low output or unstable regulation.
3. Inspect accessible hydraulic unit connectors and wiring for damage or poor contact that could disrupt pump or pressure-control operation.
4. Check for external fluid leaks around the transmission, pump, and hydraulic unit that could reduce available fluid.
5. Have hydraulic pressure and pump operation tested against the manufacturer's specification to identify internal leakage, wear, or a regulation fault.

Common fixes

• Correct the fluid level and address the source of any fluid loss.
• Repair damaged or poorly connected hydraulic unit wiring or connectors.
• Repair or replace a worn hydraulic pump if pressure testing confirms weak output.
• Repair internal leakage or the pressure regulation or accumulator fault identified by testing.

Can I keep driving?

Avoid driving if the transmission slips, loses drive, or enters limp mode; pressure failure can worsen quickly and leave the vehicle unable to move safely. If shifts are abnormal, arrange recovery rather than continuing the trip.