P0945: Hydraulic Pump Relay/Control Circuit/Open
What to do
Two very different symptoms come from this one part: the gearbox not working at all, or the battery going flat when the car stands. If either is happening, mention it — the relay is inexpensive and it is worth eliminating before the pump is condemned.
What this code means
A fault in the circuit controlling the hydraulic pump relay. The failure directions are opposite in consequence and worth separating before anything is replaced, in the same way as the transmission module's own power relay under P0885.
A relay that will not close means no pump, therefore no pressure, therefore a gearbox that cannot operate — the car stops. A relay whose contacts have welded means the pump runs whenever there is power, which overheats and destroys it, and continues drawing current with the vehicle parked until the battery is flat.
So a car that will not move and a car with a mysterious overnight battery drain can be the same inexpensive relay failing in opposite directions.
Likely causes
Start here
- Faulty hydraulic pump relay · easy
- Open circuit in relay control wiring · moderate
- Corroded or loose connector · easy
Less common
- Blown fuse or failed supply · easy
Rare
- Faulty transmission control module · specialist
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
Be the first to write this up
Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.
What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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