P2603
Coolant Pump Control Circuit Low
The electric coolant pump drive line reads below the lower threshold — typically a short to ground or a failed driver stage.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: medium
Common causes
Ordered by how often each turns out to be the cause.
- Drive line shorted to groundCommon
- Driver stage failedPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Electric Coolant Pump
- Coolant Pump Wiring
P2603 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.