What Does P2603 Mean?
The PCM has detected abnormally high voltage in the coolant pump control circuit. This suggests an open circuit, loss of ground, or short to voltage in the control wiring.
Common Causes
35%
Open circuit in coolant pump control wiring or poor connection
25%
Failed electric coolant pump motor with open internal windings
20%
Damaged or corroded pump ground connection or circuit
12%
Short to voltage in pump control circuit wiring
8%
Faulty PCM coolant pump driver circuit stuck high
Diagnostic Steps
1
Step 1: Check coolant pump connector for loose pins, corrosion, or poor terminal tension
2
Step 2: Measure voltage at pump connector with ignition on and pump commanded on (should see battery voltage on power side)
3
Step 3: Disconnect pump and measure resistance across pump motor terminals (compare to specifications, typically 0.5-5 ohms)
4
Step 4: Verify ground circuit continuity from pump to chassis/battery negative with ohmmeter
5
Step 5: Check control circuit continuity from PCM to pump; inspect for breaks or damaged insulation
Estimated Repair Cost
$150 - $750
Parts + labor, varies by vehicle and location
The PCM has detected abnormally high voltage in the coolant pump control circuit. This suggests an open circuit, loss of ground, or short to voltage in the control wiring.
The most common cause of P2603 (Coolant Pump "A" Control Circuit High) is: Open circuit in coolant pump control wiring or poor connection
Typical repair costs for P2603 range from $150 to $750, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Coolant pump inoperative or intermittent operation may cause engine overheating. Monitor temperature gauge closely and stop driving if overheating occurs.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P2603 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Cooling System
Difficulty
Type
Generic (SAE)
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
