P2603 – Coolant Pump A Control Circuit High (OBD2)
P2603 means "Coolant Pump A Control Circuit High". The voltage in the electric coolant pump circuit is above the permitted maximum. For most sensors this points to an open signal or ground wire – the signal "floats" up to the reference voltage – or to a short to voltage.
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P2603 quick summary
| Fault code | P2603 |
|---|---|
| Meaning | Coolant Pump A Control Circuit High |
| System | Powertrain (Engine & Transmission) |
| Vehicles | Generic OBD2 |
| Severity | High |
| Can I drive? | Not recommended if it is the main coolant pump – watch the temperature gauge and stop at once if it rises. An auxiliary pump fault usually allows careful driving. |
| Repair cost | €100 – €900 |
How the electric coolant pump works
Many modern engines use an electrically driven coolant pump controlled by the engine control unit; these codes mean the pump's control circuit or performance is faulty.
An electric coolant pump can run at variable speed – or stop completely – independent of engine speed. That lets the engine warm up faster, cool the turbocharger after switch-off and save fuel. On some engines it replaces the belt-driven water pump completely; on others it is an auxiliary pump for the heater, turbo or intercooler.
The control unit drives the pump with a PWM signal and receives feedback on speed, current or faults. Codes report an open, low or high control circuit and a pump that does not reach the commanded speed.
Pumps fail because of worn bearings, electronics failures, air in the cooling system or coolant leaking into the electronics. A failed main pump can make the engine overheat within minutes.
Symptoms of P2603
- Engine overheating or temperature warning
- Reduced power to protect the engine
- Heater blows cold
- Check Engine light
- Coolant level dropping or coolant around the pump
Most common causes of P2603 (most likely first)
Mechanic's Pro Tip
After replacing an electric coolant pump, always run the manufacturer's bleeding routine with the scan tool. An air pocket can make the new pump report a fault or let the engine overheat.
1.Open circuit in the signal or ground wire
Most likelyA loose ground connection is a very common cause.
2.Signal wire shorted to the 5 V reference or battery voltage
3.Faulty electric coolant pump
4.Air in the cooling system
Can make the pump run dry and report a fault.
5.Corroded connector or wiring fault
6.Low coolant level or a leak
Step-by-step diagnostic guide
- 1
Read codes and watch temperatures
Read all codes and watch coolant temperature and pump command/speed in live data.
- 2
Check signal and ground
With the ignition on and the electric coolant pump plugged in, back-probe the signal and ground wires. A signal stuck at reference or battery voltage points to an open ground/signal wire or a short to voltage.
Multimeter: Ground wire to battery negative: below about 0.1 V. Signal stuck at about 5 V (or 12 V) = open or short to voltage.
- 3
Check coolant level and bleeding
Check the coolant level and bleed the system – many vehicles have a scan tool bleeding routine that runs the pump.
- 4
Check fuse, supply and control signal
Measure the pump supply and ground and check the control signal.
Multimeter: Supply near battery voltage; PWM control signal changing with the command.
- 5
Run the pump test
Use the scan tool's actuator test to run the pump and listen or feel for flow.
- 6
Replace and bleed
Replace the pump, refill with the correct coolant and run the bleeding routine.
Frequently asked questions
Can I keep driving with P2603?
Not recommended if it is the main coolant pump – watch the temperature gauge and stop at once if it rises. An auxiliary pump fault usually allows careful driving.
How much does it cost to fix P2603?
Typical repair costs are 100 € – 900 €, depending on the cause and the vehicle. The most common fixes are: open circuit in the signal or ground wire; signal wire shorted to the 5 V reference or battery voltage; faulty electric coolant pump. Always confirm the cause with the tests above before buying parts.
Can I drive with an electric coolant pump fault?
If it is the main coolant pump, only with extreme care and while watching the temperature – it can overheat the engine quickly.
Why does the pump run after I switch off the engine?
Many engines run the pump after switch-off to cool the turbocharger. That is normal.
What is the difference between P2603 and similar codes?
P2603 belongs to a group of codes for the same component that differ in the type or location of the fault: P2600 – Coolant Pump A Control Circuit/Open; P2601 – Coolant Pump A Control Range/Performance; P2602 – Coolant Pump A Control Circuit Low. The tests on this page apply to the whole group; the type of fault tells you where to start.
Related fault codes
This guide is for information only. Working on vehicles can be dangerous — if you are unsure, have the car checked by a qualified mechanic. Values can differ between model years; always check the manufacturer's repair information.