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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Common Symptoms
- Coolant pump running at maximum speed constantly
- Battery drain from excessive pump operation
- Excessive coolant pump noise
- Check engine light on
Probable Causes (Ranked by Likelihood)
- 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
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
Step-by-Step Diagnostic Procedure
-
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)
Commonly Affected Vehicles
- 2012-2020 BMW 428i
- 2010-2018 Toyota Prius C
- 2014-2020 Ford Escape Hybrid
- 2013-2020 Chevrolet Spark EV
Related Codes
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