What is OBD-II Code P2603 – Coolant Pump A Control Circuit High

In the world of automotives, there is no shortage of acronyms and codes that can be confusing to the average person. However, despite their complexity, these codes are essential in diagnosing issues with your car. One such code is OBD-II Code P2603 – Coolant Pump A Control Circuit High, which can be seen displayed on your car’s dashboard. In this article, we’ll break down what this code means, why it’s crucial, and how an experienced mechanic can repair the issue.

What is OBD-II Code P2603 – Coolant Pump A Control Circuit High?

The OBD-II code P2603 – Coolant Pump A Control Circuit High is a diagnostic trouble code (DTC) that refers to a malfunction in the system that controls the coolant pump. The coolant pump is a crucial component in your car, responsible for moving coolant throughout the engine to prevent overheating. The system is closely monitored by your car’s computer, which uses sensors to detect any changes or malfunctions.

When the coolant pump control circuit detects that the system is not functioning correctly, it triggers the P2603 code. This code signifies that the car’s computer has detected a higher than normal voltage reading in the coolant pump’s A control circuit. This can occur due to several reasons, such as a faulty coolant pump relay, a damaged coolant pump, or a damaged engine control module (ECM).

Why is P2603 Code Important?

The P2603 code is essential because it indicates that there is a problem with your car’s coolant system, which is an integral part of your engine. If the coolant system fails, it can lead to engine overheating, which can cause significant damage to the engine, resulting in expensive repairs.

Furthermore, the code can also cause your car to fail its emissions test, which is required by law in most states. Therefore, it’s crucial to get the problem fixed as soon as possible, as ignoring it can lead to more severe issues down the line.

How to Repair the issue

The following steps can help you repair the issue:

Step 1: Check the coolant pump’s relay

As mentioned earlier, a damaged coolant pump relay can cause the P2603 code to appear. You’ll need to check the relay by connecting a multimeter to the relay connector. If the resistance reading is higher than the manufacturer’s specification or shows an open circuit, you’ll have to replace the relay.

Step 2: Check the coolant pump

If the relay is in good condition, the issue could be the coolant pump itself. To test the pump, you’ll need to apply power directly to it by connecting it to a 12V battery. If the pump doesn’t start or produces unusual noises, it indicates that it’s malfunctioning and requires replacement.

Step 3: Check the engine control module

If you’ve checked both the relay and the coolant pump, and they’re in good condition, the issue could be with the engine control module (ECM). In this case, you’ll need professional help since it requires diagnosing the ECM’s onboard circuitry and could potentially require an ECM replacement.

Frequently Asked Questions

1. What happens if I ignore the P2603 code?
Ignoring the P2603 code could lead to further issues with your car’s engine and emissions system, resulting in more expensive repairs down the line. It’s crucial to get the issue diagnosed and fixed as soon as possible.

2. Can I still drive my car with the P2603 code?
It’s not recommended as your engine could overheat, resulting in severe damage to the engine. The code also potentially causes your car to fail its emissions test, which could lead to significant penalties if ignored.

3. Can I repair the issue myself?
If you’re an experienced mechanic, you may be able to diagnose and repair the issue yourself, but we strongly recommend taking your car to a professional mechanic.

4. How much does it cost to repair the P2603 code?
The cost of repairing the P2603 code depends on the severity of the damage. Typically, it can cost around $200 to $750 for parts and labor.

5. How can I prevent the P2603 code from happening again?
Maintaining your car’s coolant system by regularly checking the coolant level, replacing the coolant pump, and checking the relay, can help prevent the P2603 code from happening again.


The OBD-II code P2603 – Coolant Pump A Control Circuit High is a crucial diagnostic code that signifies an issue with your car’s coolant system. It’s essential to get the issue checked by a professional mechanic, as ignoring it can lead to more severe issues and expensive repairs down the line. Regular maintenance of your car’s coolant system can prevent the code from occurring again, ensuring that your car runs efficiently and smoothly.

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