P0943: Hydraulic Pressure Unit Cycling Period Too Short
What to do
If you can hear the gearbox pump running very frequently, that is this fault and it is worth acting on now rather than later. The pump was designed to run occasionally; running constantly destroys it, and a cheap leak left alone turns into an expensive pump replacement plus the same leak still to fix. Ask specifically whether the accumulator pre-charge was checked, since that is often serviceable on its own.
What this code means
The pump is running again too soon after it last stopped. This is the code that puts a number on the leak described under P0933, and it is one of the more genuinely useful diagnostics in this range because it catches a problem while it is still cheap.
The accumulator exists so the pump need not run continuously: it is charged once, then the stored pressure serves several gear changes before the pump runs again. How long that takes is a direct measurement of how well the system holds pressure. A healthy circuit goes minutes between pump runs. One that cycles every few seconds is losing pressure as fast as it makes it.
The important part is what happens next if it is ignored. These pumps are sized on the assumption of intermittent duty. Running near-continuously overheats the motor and wears the brushes and bearings at many times the intended rate, so a leaking seal that costs comparatively little to replace destroys a pump that costs a great deal more — and the pump failure is usually what finally brings the car in. By that point the leak is still there and still needs fixing, so the bill is both parts.
The leak itself is usually a seal in an actuator, a valve not seating, or an accumulator that has lost its gas pre-charge. That last one is worth checking early, because it is often a serviceable item rather than a whole assembly.
Likely causes
Start here
- Hydraulic system leak · specialist
- Failed accumulator charge · specialist
- Low hydraulic fluid level · easy
- Leaking actuator seal · specialist
Less common
- Faulty hydraulic power unit · specialist
- Faulty hydraulic pressure sensor · moderate
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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