P2603: Coolant Pump A Control Circuit High
What to do
The car will often feel normal. Ask for the pump's own fuse to be checked first — it has a dedicated high-current supply, and a blown fuse looks exactly like a broken wire until someone opens the box. If a new fuse blows straight away, the pump itself has failed and that is worth knowing before more time is spent on wiring.
Meanwhile keep an eye on the temperature gauge in slow traffic, and be aware that on a turbocharged engine the pump normally runs on for a few minutes after switch-off to protect the turbocharger — which is the part of this fault that does harm quietly.
What this code means
The coolant pump control circuit reads above its valid range — an open circuit, a disconnected connector, or a short to supply.
The practical result is normally a pump that cannot be commanded, so the consequences are those set out at P2600: reduced cooling capacity at low road speeds, a heater that goes cold whenever a stop-start system shuts the engine down, and — on a turbocharged engine — the loss of the run-on cycle that keeps coolant moving through the turbo bearing housing after shutdown.
The pump's own supply is worth checking before the pump. These run on a dedicated high-current feed with its own fuse, and a blown fuse presents as an open circuit indistinguishable from a broken wire until someone looks. A fuse that blows again immediately afterwards is telling you the pump has failed short, which is useful information rather than a nuisance.
Likely causes
Start here
- Blown fuse or failed supply · easy
- Open circuit in control wiring · moderate
- Disconnected sensor connector · easy
- Faulty electric coolant pump · moderate
Less common
- Wiring shorted to voltage · moderate
Symptoms
Components involved
Information, not instruction
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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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