What it means
The coolant bypass valve A is stuck in the open position. Coolant always bypasses the radiator, leading to overheating under load.
At a glance
- Usually lights the check-engine light
How it works
Coolant bypass valve A directs coolant through a bypass path in the cooling system. This code sets when the valve remains stuck open instead of moving as commanded, which can leave coolant circulating through the bypass when the system needs a different flow path.
Common causes
Most likely first.
- Valve seized open by sediment or wax
- Broken return spring
Symptoms
- Check-engine light
- Engine temperature may fluctuate
- Engine may overheat under load
How to diagnose it
- Record freeze-frame data and check live coolant temperature and bypass valve A command data to see when the stuck-open condition occurs.
- With the engine cool, inspect valve A and its linkage for binding, damage, or signs that the return spring has failed.
- Check for sediment or deposits that could hold the valve open, and verify that the valve can move through its range.
- Compare commanded and reported valve positions, if available, to confirm that valve A stays open despite commands to move.
- If the valve is mechanically free, test its actuator and control circuit using the wiring information and manufacturer's specification.
Common fixes
- Clear sediment or deposits that are binding bypass valve A.
- Repair or replace a broken return spring or damaged linkage.
- Repair a faulty actuator connection or control circuit if it prevents valve movement.
- Replace bypass valve A if it remains seized open after cleaning and linkage checks.
Can I keep driving?
Avoid heavy loads and stop driving if the temperature gauge rises above normal or an overheat warning appears; an open bypass valve can lead to overheating under load. Let the engine cool before inspecting the cooling system.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.