Coolant Pump Control Circuit High
The P2603 code indicates that the Engine Control Module (ECM) has detected a voltage signal from the coolant pump control circuit that is higher than the expected range. This typically points to a short to voltage, a faulty coolant pump, or a wiring issue. The coolant pump is responsible for circulating coolant through the engine and heater core; a malfunction can lead to overheating and reduced cabin heat.
01. Most Common Causes
- Faulty coolant pump motor
- Short to voltage in the control circuit wiring
- Damaged coolant pump relay or fuse
- Failed ECM (rare)
02. Symptoms You Will Notice
- Check Engine Light on
- Engine overheating
- Poor heater performance
- Coolant leaks near pump
03. Step-by-Step Diagnosis
Step 1: Scan for codes and record freeze frame data.
Step 2: Visually inspect coolant pump and wiring for damage or corrosion.
Step 3: Test coolant pump control circuit voltage with a multimeter (should be 12V with engine running).
Step 4: Check coolant pump relay and fuse; replace if blown.
Step 5: If circuit voltage is high, disconnect pump and retest; if voltage drops, replace pump.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
No, driving with P2603 can cause engine overheating and serious damage. Have it diagnosed and repaired promptly.
How much does it cost to fix?▼
Repair costs typically range from $150 to $400, including parts and labor. The coolant pump itself costs $50-$150, plus 1-2 hours of labor.