Coolant Pump Control Circuit High

Possible causes

• CommonFailed electric coolant pump
• CommonCorroded connector or damaged wiring
• CommonBlown fuse or failed relay
• CommonAir lock in the cooling system after a previous repair
• CommonLow coolant level
• PossibleDebris or scale jamming the pump impeller
• RareFailed control module driver

What you might notice

• Engine running hot
• Temperature gauge climbing, particularly in traffic
• Heater blowing cool
• Coolant warning
• Check engine light on
• On a turbocharged engine, the pump running after switch-off may have stopped

What to check, in order

1. Disconnect the pump and check whether the high reading persists at the harness.
2. Watch the temperature gauge and stop if it climbs. An engine without coolant circulation overheats quickly, and overheating damage is expensive and permanent.
3. Check the coolant level when the engine is cold. Never open a hot cooling system - it is pressurised and above its normal boiling point.
4. Check the fuse and relay for the pump circuit before anything else.
5. Listen for the pump. Many run at ignition-on and continue after switch-off, so silence when one should be running is a clear finding.
6. Check for an air lock if the cooling system has been opened recently - an air-locked pump cannot circulate coolant even though it is running.
7. Inspect the connector for corrosion.