P26A9: Engine Coolant Bypass Valve A Position Sensor Stop/Minimum Stop Performance

What it means

During self-calibration the bypass valve A position sensor never reached the minimum mechanical stop. The position reference cannot be zeroed.

At a glance

• Usually lights the check-engine light

How it works

During calibration, the control module moves coolant bypass valve A and uses its position sensor to learn the valve's minimum mechanical stop. This code sets when the feedback never reaches the expected minimum stop, leaving the module without a reliable low-position reference.

Common causes

Most likely first.

1. Sediment prevents valve from reaching minimum stop
2. Sensor not aligned with valve shaft

Symptoms

• Check-engine light
• Engine temperature may fluctuate
• Heating or warm-up may be affected

How to diagnose it

1. Check freeze-frame data and scan-tool calibration or position data to confirm that the failed reference is the minimum stop for bypass valve A.
2. With the engine cool, inspect valve A and its coolant passages for sediment or other obstruction that could prevent full travel.
3. Inspect the sensor alignment and its connection to the valve shaft, looking for a shifted sensor or loose mounting.
4. Observe bypass valve A's commanded and reported positions through its travel to see whether the valve reaches the low end mechanically.
5. If the valve reaches the minimum stop but feedback does not register it, test sensor alignment and circuit operation against the manufacturer's specification.

Common fixes

• Remove the obstruction or sediment preventing bypass valve A from reaching its minimum stop.
• Realign and secure the position sensor on the valve shaft.
• Repair a damaged linkage or mounting that prevents full travel.
• Replace the position sensor if it fails to register the minimum stop despite correct alignment and circuit operation.

Can I keep driving?

If the engine temperature is stable, drive gently while monitoring it and avoid demanding conditions until the valve's travel is corrected. Stop if the engine overheats or temperature becomes unstable, since bypass valve A may not regulate coolant flow as intended.