Coolant Pump Control Circuit High
The P2603 code means the vehicle's onboard diagnostic system has detected: Coolant Pump Control Circuit High. This is a moderate severity code.
- Keep driving?
- Short distances only
- DIY difficulty
- hard
- Estimated cost
- $200 - $750 (parts and labor)
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What Are the Symptoms of P2603?
- Coolant pump running at maximum speed constantly
- Battery drain from excessive pump operation
- Excessive coolant pump noise
- Check engine light on
What Causes P2603? (Most Likely First)
- Short to voltage in pump control circuit Very High
- Pump relay stuck closed High
- ECM driver circuit stuck high Moderate
- Aftermarket wiring feeding power to pump circuit Low
Can I Still Drive with P2603?
Short distances only. P2603 is rated moderate severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
Frequently Asked Questions
Will a constantly running coolant pump drain my battery?
Yes. If the pump runs continuously at full speed, especially when the engine is off, it can drain the battery within several hours.
Is overcooling the engine harmful?
Mild overcooling can reduce fuel efficiency and increase emissions. The ECM needs to control coolant flow to maintain optimal operating temperature.
Can I disconnect the pump temporarily?
In an emergency you can unplug the pump connector, but you must monitor engine temperature closely as you will lose auxiliary cooling.
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose P2603?
-
Check pump control circuit voltage with pump commanded off
-
Test pump relay for welded contacts
-
Verify ECM can modulate pump speed with bidirectional control
-
Inspect for aftermarket wiring modifications
Sources 1
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
Which Vehicles Commonly Get P2603?
- 2012-2020 BMW 428i
- 2010-2018 Toyota Prius C
- 2014-2020 Ford Escape Hybrid
- 2013-2020 Chevrolet Spark EV
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