P2600: Coolant Pump A Control Circuit/Open
What to do
The car may drive entirely normally, and that is exactly why this is worth dealing with promptly rather than leaving. On a turbocharged engine this pump usually keeps running for a few minutes after you switch off, and that run-on is what stops heat soaking into the turbocharger and baking the oil in its bearing. Losing it does no harm on any single journey and does real harm over months, invisibly, after the car has been parked.
Two things to watch for and report. If the heater goes cold whenever the engine stops at a junction and warms up again as it restarts, that is this fault — the electric pump is what keeps hot coolant moving while the engine is off. And keep an eye on the temperature gauge in slow traffic, since an electric pump is doing most of the work at low speeds.
Ask for the fuse, the connector and the wiring to be checked before the pump is replaced; an open circuit is more often one of those than the pump itself.
What this code means
An open circuit in the control output driving an electrically powered coolant pump.
A belt-driven water pump has one flaw that no amount of engineering can remove: its speed is tied to engine speed, and that relationship is backwards. An engine needs the most cooling when it is working hard at low speed — crawling in traffic on a hot day, towing up a long climb — which is exactly when a belt pump is turning slowly and the airflow through the radiator is weakest. At a motorway cruise it needs relatively little, and the pump is spinning fast. An electric pump breaks that link: it runs at whatever rate the module asks for, based on temperature rather than on engine speed.
The more important thing it can do is run when the engine is not running at all, and that is where a fault here becomes expensive in a way nobody sees coming.
On a turbocharged engine, shutting down is the hottest moment the turbocharger experiences. While the engine runs, oil and coolant carry heat away from the bearing housing continuously. Switch off, and that flow stops while the turbine — which has just been glowing — is still soaking heat back into the housing. If nothing moves the coolant, it boils where it sits and the oil in the bearing housing bakes onto the shaft as carbon. This is the slow mechanism behind a large share of turbocharger failures, and the run-on pump exists to prevent it. It cycles for a few minutes after the key is turned off, which is why a modern car sometimes hums quietly to itself in a garage.
So a failed pump control circuit can be damaging a turbocharger after the driver has parked and walked away, with nothing wrong while driving. The temperature gauge is normal, the engine behaves perfectly, and the harm is done in a car park. That is an unusual failure shape and it is the reason this code is worth acting on rather than filing.
The same pump does other work on vehicles that stop their engines: on a stop-start car or a hybrid the engine is frequently off while the cabin still wants heat, and only an electric pump can keep the heater matrix supplied. A heater that goes cold every time the engine stops at a junction, and warms again as it restarts, is this fault rather than a heating fault.
An open circuit means the module's command never reaches the pump. The connector, the wiring and the pump's own supply fuse are the ordinary places to look before the pump itself.
Likely causes
Start here
- Open circuit in control wiring · moderate
- Blown fuse or failed supply · easy
- Corroded or loose connector · easy
- Faulty electric coolant pump · moderate
Less common
- Damaged wiring harness · moderate
Rare
- Faulty engine 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.
Sign in or create an account to add what you found about P2600.