Coolant Pump Control Circuit High
The P2603 code indicates that the Engine Control Module (ECM) has detected a high voltage condition in the control circuit of the auxiliary coolant pump. This pump is responsible for circulating coolant through the heater core and other components when the engine is off, such as during stop-start events or for cabin heat. A high voltage signal suggests a short to power, a faulty pump, or an issue with the wiring or connector.
1. Most Common Causes
- Faulty or internally damaged electric coolant pump
- Short circuit to voltage in the control circuit wiring
- Open or loose ground connection in the pump circuit
- Corroded, bent, or damaged pins in the electrical connector
- Coolant pump control relay stuck closed
- Internal failure in the engine control module (ECM)
2. Symptoms You Will Notice
- Check Engine Light on
- Insufficient cabin heat
- Engine overheating in stop-and-go traffic
- Coolant leaks near the pump
3. Step-by-Step Diagnosis
Step 1: Scan for additional codes and check freeze frame data.
Step 2: Visually inspect the coolant pump and its connector for damage or corrosion.
Step 3: Test the pump control circuit voltage with a multimeter; compare to manufacturer specs.
Step 4: Check for shorts to power by disconnecting the pump and measuring voltage at the harness.
Step 5: If circuit is okay, test pump resistance and operation; replace if faulty.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended. The coolant pump may fail, leading to overheating or loss of cabin heat. Have it diagnosed promptly.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, including parts and labor. The pump itself costs $50-$150, plus diagnostic time.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.