Easy one-page printout for the garage or repair shop
This summary uses the existing diagnostic information shown in full below.
This code means that a part in your car's cooling system, called the bypass valve, isn't working right. It's supposed to move and control the flow of coolant, but it's stuck open, like a door that won't close.
The P26AB code indicates that the engine control module (ECM) has detected that the engine coolant bypass valve 'A' is stuck in the open position.
The engine coolant bypass valve is responsible for controlling the flow of coolant through the engine. When the valve is stuck open, it can cause the engine to run inefficiently by allowing too much coolant to bypass the engine, potentially leading to overheating or poor heater performance.
• Check Engine Light is on
• Engine overheating
• Poor heater performance
• Faulty engine coolant bypass valve
• Wiring issues or poor electrical connections
• Malfunctioning ECM
ECM: Engine Control Module
OBD-II: On-Board Diagnostics, Second Generation
• Use an OBD-II scanner to confirm the code.
• Inspect the wiring and connectors for damage.
• Test the operation of the coolant bypass valve.
• Replace the engine coolant bypass valve.
• Repair or replace damaged wiring or connectors.
• Reprogram or replace the ECM if necessary.
• OBD-II scanner
• Multimeter
• Wrench set
$150 - $400
Moderate
• Ford Fusion
• Chevrolet Malibu
• Honda Accord
• Regular maintenance checks
• Ensure coolant system is free of debris
• Check for leaks regularly
Engine Performance
• Have your vehicle inspected by a professional.
• Avoid driving long distances until the issue is resolved.
Check with your vehicle manufacturer for warranty coverage on cooling system components.
This code has been more prevalent in vehicles with higher mileage or those that have not had regular coolant system maintenance.
Moderate – Should be addressed soon to prevent engine overheating.
Driving with a malfunctioning cooling system can lead to engine damage and is not recommended.
• Engine at operating temperature
• Vehicle in park or neutral
The engine coolant bypass valve is typically located near the thermostat housing or along the coolant hoses.
Q: Can I drive with a P26AB code?
A: It's not recommended to drive for long distances as it can lead to engine overheating.
Q: How do I know if the coolant bypass valve is bad?
A: Symptoms include engine overheating, poor heater performance, and the Check Engine Light being on.
High-End · Full-system diagnostics
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Universal · Digital multimeter
A solid entry-level multimeter for voltage, continuity, resistance, and basic electrical troubleshooting.
Helpful for checking voltage drops, grounds, and basic circuit health when modules are not communicating.
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Universal · Wire connectors and repair kit
Useful when diagnosis points toward damaged wiring, corroded terminals, or connector repairs.
Useful if diagnosis points toward damaged connectors, wiring, or terminal repairs.
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Fitment Required · Vehicle-fitment part
Relevant when coolant-temperature and warm-up faults indicate a thermostat-related issue.
Coolant-temperature and warm-up faults often lead to thermostat testing and replacement.
Thermostats are vehicle-specific and should be matched by engine and housing style.
View options on AmazonThese parts may be related to this fault category, but a code by itself does not confirm exact fitment or guarantee that replacing a part will solve the problem.