OBD-II trouble code
P0942: Hydraulic Pressure Unit
A verdict on an entire assembly rather than a fault in one circuit. The module has judged that the unit which makes and stores hydraulic pressure is not doing its job — without saying which piece of it failed.
Quick facts
- System
- Powertrain
- Category
- Transmission / Pressure Control
- Severity
- High severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $150 – $3,200
- DIY difficulty
- Shop recommended
Browse every code in P0900–P0999, or start from the full code library.
What does P0942 mean?
Almost every code in this part of the range names a wire, a sensor or a solenoid. P0942 names a box. That difference is what the page has to explain, because it changes both the diagnosis and the conversation about money.
The hydraulic pressure unit — power unit, power pack, hydraulic control unit, depending on whose manual you read — is the self-contained assembly that supplies the muscle for an automated manual or dual-clutch transmission. Inside it are an electric pump motor, a small accumulator that stores pressurised fluid so the system can act instantly without waiting for the pump, a pressure sensor, and a block of valves that direct that pressure to the clutch and shift actuators. There is no engine-driven pump and no torque converter involved. The unit is a closed electro-hydraulic power supply, and everything the transmission physically does depends on it.
The module does not test the individual pieces. It tests an outcome: when I command pressure, does pressure appear, and does it stay where I put it? P0942 is what gets stored when that outcome is wrong and the module cannot attribute the failure to a specific circuit it monitors separately. So the code is a system-level conclusion, and turning it into a repair means decomposing that conclusion. A pump that will not spin, a pump that spins but cannot build, an accumulator that has lost its ability to hold, a valve stuck open, a filter blocked, or simply not enough fluid in the circuit all produce the same verdict from the module's point of view.
That decomposition is worth doing carefully, because the fluid-side answers are cheap and the hardware answers are not. Low fluid level, a clogged filter or screen, and degraded fluid that has thickened or foamed are all real causes of this code, all correctable for a few hundred, and all commonly skipped in a rush to condemn the assembly. Checking them first is not diagnostic ritual — it is the difference between a service and a four-figure part.
There is a commercial reality to state plainly as well. On most vehicles the pressure unit is supplied only as a complete assembly. The pump motor is not sold separately, the accumulator is not sold separately, and the valve block is not serviceable. So once the fault is inside the unit, proving exactly which internal component failed makes no difference to the invoice — the whole assembly is what gets fitted. That is also why the cost range on this code is so wide, and why the useful diagnostic effort goes into the questions that can still change the outcome: is this fluid-related, is it electrical supply to the unit, or is it genuinely internal.
One final point on what to expect from the car. The transmission does not usually fail all at once on this code. It degrades: slow or hesitant engagement from rest, shifts that take longer than they should, a reluctance to select at all when the fluid is cold. That degradation is a warning worth acting on quickly, because the failure mode this system eventually reaches is an inability to select a gear at all, and it does not choose a convenient moment to get there.
Common causes
- Low hydraulic fluid level in the actuator circuit
- Blocked filter or suction screen inside the pressure unit
- Electric pump motor worn, seized or drawing excessive current
- Accumulator no longer able to store pressure
- Internal valve stuck open or leaking past its seat
- Degraded or incorrect hydraulic fluid affecting pump performance
- Internal seal leakage bleeding pressure back to the reservoir
- Poor power supply or ground to the pump motor
- Pressure sensor within the unit reporting incorrectly
- Control module fault in the pressure unit drive or monitoring circuit
Symptoms
- Slow or hesitant engagement when pulling away
- Gear changes taking noticeably longer than normal
- Transmission warning message alongside the check engine light
- Reluctance to select a gear, worst when the fluid is cold
- Pump audible for longer periods than it used to be
- Limp mode or a restricted set of gears under load
- Occasional inability to select drive or reverse
- Warning that clears after a restart and returns later the same day
- Clutch engagement quality varying journey to journey
- Complete loss of gear selection in the later stages
Diagnostic steps
- 1.Check the hydraulic fluid level and condition first, because the cheap answers to this code all live on the fluid side and are routinely skipped.
- 2.Inspect the filter or suction screen for blockage before assuming the pump has failed.
- 3.Confirm the fluid is the correct specification, since a substitute with the wrong viscosity produces exactly this verdict.
- 4.Measure the supply voltage and ground quality at the pump motor under load rather than at rest.
- 5.Measure pump current draw and compare it against specification — a motor that is drawing hard and achieving little is failing mechanically.
- 6.Command a pressure build with the scan tool and watch whether pressure appears at all and how fast.
- 7.Observe whether the achieved pressure then holds or decays, which separates a supply problem from a leak.
- 8.Read every stored code together, because a separately reported sensor or relay fault will explain this verdict without the unit being at fault.
- 9.Check for external fluid loss around the unit, its pipework and the actuators.
- 10.Establish whether the pressure unit is available as separate components on this vehicle before quoting, as most are assembly-only.
Repair cost
$150 – $3,200
Diagnosis is $120 to $280 and should always include a fluid level and condition check before anything is condemned. A fluid service with a filter is $180 to $500 and is the outcome worth hoping for. An electrical supply or ground repair to the pump is $120 to $400. A complete hydraulic pressure unit is the expensive end: $650 to $2,400 for the assembly plus 2 to 9 hours of labour depending on whether it is accessible from above or the transmission has to come out, so $1,200 to $3,200 fitted is realistic. Insist that the fluid-side checks were done before approving an assembly.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with hydraulic power unit / pump assembly replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
Leave this one to a qualified shop. It typically involves emissions-critical components, refrigerant handling, or other work that requires manufacturer-grade tooling, training, or certification. DIY attempts often produce a more expensive problem than the original code.