P2603 Code: Coolant Pump Control Circuit High

What the P2603 code means

Many modern engines use electric coolant pumps, or mechanical pumps with a controlled clutch. The computer decides when to circulate coolant so the engine warms up sooner and so the turbo is cooled after you shut the engine off.

The computer watches the control circuit from its own driver transistor. The P2603 code reports high voltage in the control circuit (an open circuit or a short to voltage). Before you replace the component, check the fuse, relay, connector and wiring, which are the most common cause.

Some pumps talk to the computer with a PWM signal or over the LIN bus.

To confirm it, measure the continuity of each wire between the component connector and the computer connector with the key off. It should be under 1 ohm, and an infinite reading means that wire is open. If the wiring is good, measure the component itself: an infinite resistance confirms it is open inside.

P2603 code symptoms

• Check engine light or another warning light on.
• Overheating of the engine or the turbo.

Likely causes of the P2603 code

1. Loose or broken connector. The most frequent cause, especially after another repair.
2. Open coil or motor, with infinite resistance.
3. Control wire cut between the component and the computer.
4. Short to 12 V, where the control wire touches another wire that carries voltage.

How to diagnose the P2603 code step by step

1. Command the component with the scan tool and check whether it responds.
2. Check the fuse and relay. Measure voltage on both sides of the fuse and swap the relay with an identical one.
3. Measure the supply at the connector: battery voltage with the key on or when it is commanded.
4. Measure the component resistance and compare it with the manual, and check the insulation to ground too.
5. Check the control wire: continuity to the computer and no short circuits.

How to fix the P2603 code

• Repair the connector, the wiring or the supply.
• Replace the coolant pump if it does not respond with correct supply and command.
• Clear the codes and verify.

Technical reference data

• 12 V supply and PWM or LIN control.
• Approximate values only: check the manufacturer data for your vehicle.

Brand-specific notes

If the code appeared right after other work under the hood, go straight to the pump connector. A plug that was not seated again is the most common reason for the P2603 code.

P2603 on BMW

Common on BMW, where the main coolant pump is electric.

P2603 on Volkswagen and Audi

Common on these makes, where an auxiliary pump is used.

P2603 on Ford EcoBoost and Mercedes-Benz

Also common on Ford EcoBoost engines and on Mercedes-Benz.

Frequently asked questions about P2603