Coolant Pump "A" Control Circuit/Open
The PCM detected an open or abnormal condition in the Coolant Pump A control circuit, preventing proper electrical communication with the coolant pump. This circuit controls the electric coolant pump's operation, and when open, the engine cannot regulate coolant flow effectively, causing the cooling system to operate inefficiently.
What You Might Notice
- Cooling fans running at maximum speed continuously
- Engine overheating or running hotter than normal
- Check Engine Light illuminated
- Reduced fuel economy due to constant fan operation
- Potential coolant overflow or hot coolant smell
Most Common Causes
- 1
Damaged wiring or connectors in pump circuit
Broken wires, corroded connectors, or loose connections in the coolant pump control circuit prevent proper signal transmission from the PCM to the pump.
- 2
Faulty coolant pump relay
A defective relay fails to complete the circuit when the PCM signals it, blocking power delivery to the coolant pump motor.
- 3
Failed electric coolant pump motor
The coolant pump motor itself may be internally open or have failed windings, breaking the electrical circuit regardless of relay function.
- 4
PCM module fault or programming issue
A malfunctioning PCM may be unable to properly control the coolant pump circuit output, though this is less common than external circuit failures.
How to Diagnose It
- 1
Check Damaged wiring or connectors in pump circuit — Broken wires, corroded connectors, or loose connections in the coolant pump control circuit prevent proper signal transmission from the PCM to the pump.
- 2
Check Faulty coolant pump relay — A defective relay fails to complete the circuit when the PCM signals it, blocking power delivery to the coolant pump motor.
- 3
Check Failed electric coolant pump motor — The coolant pump motor itself may be internally open or have failed windings, breaking the electrical circuit regardless of relay function.
- 4
Check PCM module fault or programming issue — A malfunctioning PCM may be unable to properly control the coolant pump circuit output, though this is less common than external circuit failures.
How to Fix It
- 1
Inspect and repair wiring harness
Carefully inspect the coolant pump control circuit wiring for breaks, corrosion, or poor connections. Repair or replace damaged wires and clean corroded connectors with appropriate contact cleaner.
- 2
Test and replace coolant pump relay
Use a multimeter to test the relay for proper continuity and switching function. Replace the relay if it fails to switch properly when energized.
- 3
Test coolant pump motor resistance
Disconnect the pump and measure its winding resistance with a multimeter. If resistance is infinite or extremely high, the motor is open and must be replaced.
- 4
Clear code and perform system retest
After repairs, clear the diagnostic trouble code using a scan tool and run the engine to verify normal operation. Monitor coolant temperature and fan duty cycle to confirm the repair.
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