What is OBD-II Code P26AC – Engine Coolant Bypass Valve B Control Circuit/Open

Unleashing the Mystery Behind OBD-II Code P26AC: Engine Coolant Bypass Valve B Control Circuit/Open

As a car owner, one of the things you must be familiar with is OBD-II codes. These codes indicate a problem in your car’s engine system, transmission, or emissions control. From a mechanic’s perspective, understanding these codes is vital in diagnosing and repairing the issue. One of the common codes that you may encounter when your check engine light illuminates is OBD-II Code P26AC – Engine Coolant Bypass Valve B Control Circuit/Open. In this article, we’ll explore the meaning of this code, its possible causes and symptoms, and how to fix it.

What is OBD-II Code P26AC – Engine Coolant Bypass Valve B Control Circuit/Open?

OBD-II Code P26AC means that the engine control module (ECM) has detected an open circuit or malfunctioning component in the engine coolant bypass valve B control circuit. This valve allows the engine to regulate the flow of coolant by diverting it away from the engine block. By doing so, it helps the engine warm up faster during cold temperatures, which is essential for optimum performance and fuel economy. The ECM monitors the voltage signals sent by the engine coolant bypass valve B control circuit to determine whether the valve is functioning correctly.

What are the possible causes of OBD-II Code P26AC?

Several factors can contribute to the OBD-II Code P26AC. Some of the common causes include:

1. Faulty Engine Coolant Bypass Valve – The engine coolant bypass valve may malfunction due to wear and tear, corrosion, or electrical issues. If the valve fails to function correctly, it affects the engine’s ability to warm up properly, leading to decreased fuel efficiency and power output.

2. Damaged Wiring or Connectors – Any interruption in the engine coolant bypass valve B control circuit caused by damaged wiring or connectors may trigger the P26AC code. Water, oil, or debris accumulation may also cause a malfunction in the connectors or wires, leading to an open circuit.

3. Failed Engine Coolant Temperature Sensor – The engine coolant temperature sensor may fail due to an internal fault, exposure to extreme heat or cold, or short circuit. When this happens, the ECM may not receive the correct temperature signals from the sensor, leading to code P26AC.

4. Failed Engine Control Module – While this is a less common cause, a faulty ECM may cause the P26AC code to display. The ECM may fail due to a power surge, faulty programming, or other internal malfunctions.

What are the symptoms of OBD-II Code P26AC?

When the P26AC code appears, it triggers the check engine light to illuminate. Other symptoms may include:

1. Reduced Fuel Economy – A malfunctioning engine coolant bypass valve affects the engine’s ability to warm up quickly and efficiently, leading to reduced fuel economy.

2. Rough Idle – The engine may not maintain a stable idle if the bypass valve is not performing its function correctly.

3. Engine Misfire – When the engine fails to warm up properly, it may cause a misfire, leading to a rough-running engine.

4. Increased Emissions – The engine may produce higher emissions as a result of the P26AC code, as the fuel combustion is not optimized.

How to Fix OBD-II Code P26AC?

The first step in fixing the P26AC code is to diagnose the source of the problem. Here are some possible solutions:

1. Check the Engine Coolant Bypass Valve – Inspect the engine coolant bypass valve for wear and tear, corrosion, or any electrical faults. If it’s faulty, replace it with a new one.

2. Inspect the Wiring and Connectors – Check the wiring and connectors in the bypass valve B control circuit for any corrosion, wear, or debris accumulation. If necessary, repair or replace the damaged wiring or connectors.

3. Test the Engine Coolant Temperature Sensor – Test the engine coolant temperature sensor using a digital multimeter to see if it’s functioning correctly. If it’s malfunctioning, replace it with a new one.

4. Check the Engine Control Module – While ECM failure is rare, it’s still possible. If all the above components are working correctly, inspect the ECM for any damage or malfunction. Replace the ECM if necessary.

Frequently Asked Questions:

1. Can I still drive my car with OBD-II Code P26AC – Engine Coolant Bypass Valve B Control Circuit/Open?

Yes, you can still drive your car with the P26AC code, but it’s best to have it diagnosed and repaired as soon as possible.

2. How much does it cost to repair OBD-II Code P26AC?

The cost of repairing the P26AC code may vary depending on the root cause of the issue. On average, the cost ranges from $100 to $500.

3. How do I reset the check engine light after fixing the P26AC code?

You can reset the check engine light using a scan tool or by disconnecting the car battery for a few minutes.

4. How often should I check my car for OBD-II codes?

You should check your car for OBD-II codes regularly, especially if you notice any unusual symptoms or changes in performance.

5. Is it safe to drive with the check engine light on?

It’s best not to ignore a check engine light, as it indicates a problem with your car’s engine system. Continuing to drive with a check engine light on may lead to severe damage to your engine or emissions control system.


OBD-II codes may sound confusing and intimidating to an average person, but with some basic knowledge, you can easily understand their meaning and take appropriate action. When facing the P26AC code, don’t panic. Instead, take your car to a qualified mechanic for diagnosis and repairs. By doing so, you can prevent further damage to your car’s engine and ensure that it performs at its best. Always remember to check your car regularly for any unusual symptoms or changes in performance and take preventative measures to maintain its longevity and safety.

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