P2603: Coolant Pump A Control Circuit High

P2603 means the drive line of electric coolant pump A reads high - usually a short to the supply side, or an overcurrent seen by the driver stage. Ford's 2020-2023 gasoline OBD summary assigns pump A to the auxiliary high-temperature loop for cabin heating and sets P2602/P2603 when the smart driver reports a fault within 5 s. For the 3.6 L LLT, GM's 2008 table checks the after-run pump for a circuit fault to voltage (pending code only, no warning light). VW's 2014 books use a current threshold: about 0.60-1.20 A on the Passat and CC, 5.5-10 A on the Touareg. Under CARB, output components need monitoring for circuit faults. P2600 is the open circuit, P2601 performance, P2602 the low-side fault. Heater output or after-run cooling may be lost.

Medium severity. Can I keep driving?Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

Symptoms

Fault code stored; MIL depends on the maker (GM 2008 LLT table none, GM 2023 ECM table Type B)
Weak cabin heating
Higher coolant temperature after hot shutdown

Most likely causes

Control wire shorted to battery voltage
Seized or sluggish pump drawing excessive current
Faulty driver stage in the ECM

What to check, in order

Start with the simplest. You can tick off each step.

With the engine cold, check the coolant level; never do this when the system is hot
Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
Check the actual temperature in live data
Make sure the fan comes on when it should
Check the thermostat and connector
Measure the sensor and replace it if its readings do not make sense

Good to know

Repair difficulty: medium
It affects emissions.

What each character of P2603 means

P: Powertrain: engine and transmission
2: Generic code: same on every make
6: Control modules and outputs
03: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2603?

Watch the temperature gauge. If it climbs or a warning appears, stop the car in a safe place and turn off the engine: overheating can cause serious damage.

What causes code P2603?

The most common causes are: control wire shorted to battery voltage; seized or sluggish pump drawing excessive current; faulty driver stage in the ECM.

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.