P27E3: Electric/Auxiliary Transmission Fluid Pump Control Valve Circuit/Open
What to do
The car will drive normally — the usual sign is stop-start no longer switching the engine off. That is deliberate: the module will not stop the engine when it cannot hold hydraulic pressure through the stop. Have it repaired rather than living with it, because on hybrids the same pump covers engine-off driving, and a shunt on every restart is wear the clutches were never designed to absorb.
What this code means
The auxiliary transmission fluid pump control valve circuit is open.
An open control circuit means the command never arrives. The pump itself may be perfect; the wire that tells it to run has a break, a corroded pin, or a connector left half-seated by a previous repair.
The control valve routes what the auxiliary pump makes. The pump feeds the transmission's main circuit through a valve that directs and holds its output where it is needed. When the valve's circuit fails, the pump can run perfectly and still achieve nothing — pressure goes unrouted, and the stop-start behaviour this system exists for degrades exactly as if the pump itself had failed.
Electrically this is an ordinary solenoid circuit, and it fails the ordinary ways: corroded connectors, chafed wiring, a winding gone open or shorted. The valve also lives in the valve body, so debris in ageing fluid can gum its movement while the electrical side tests perfectly.
This pump exists for the moments the engine is off. A conventional automatic makes its hydraulic pressure with a pump driven by the engine, so at a stop-start red light — engine stopped — pressure would drain away, and the first metre of drive would arrive with a thump while the mechanical pump refilled the circuit. The electric auxiliary pump holds pressure through those stops, so the clutches are already applied when the engine restarts. Hybrids lean on it even harder, because their engine stops whenever the battery can carry the load.
Which is why the commonest symptom is no symptom at all — except stop-start quietly giving up. The module knows it cannot hold pressure through an engine stop, so it stops allowing them. A car that used to switch off at the lights and no longer does, with this code stored, has already told you what is wrong. Where stops do still happen, the tell is a pause or a shunt as the car pulls away afterwards.
Likely causes
Start here
- Corroded or loose connector · specialist
- Damaged wiring harness · specialist
Less common
- Debris in the transmission fluid · specialist
- Worn valve body · specialist
Rare
- Faulty transmission control module · specialist
Symptoms
Components involved
Information, not instruction
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