P26AA: Engine Coolant Bypass Valve A Position Sensor Maximum Stop Performance

What it means

During self-calibration the bypass valve A position sensor never reached the maximum mechanical stop.

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 maximum mechanical stop. This code sets when feedback never reaches the expected maximum stop, so the module cannot establish the valve's full-travel reference.

Common causes

Most likely first.

1. Sediment prevents valve from reaching maximum 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 bypass valve A failed to register its maximum stop.
2. With the engine cool, inspect the valve and its coolant passages for sediment or obstruction that could limit travel at the high end.
3. Check that the position sensor is correctly aligned and secured on valve A's shaft.
4. Compare commanded and reported positions as valve A moves through its range to determine whether the valve reaches its maximum stop.
5. If mechanical travel reaches the maximum stop but the sensor does not report it, check sensor alignment and circuit operation against the manufacturer's specification.

Common fixes

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

Can I keep driving?

If engine temperature remains normal, drive gently and monitor it closely; avoid heavy loads until the valve's full travel is restored. Stop if the engine overheats or temperature becomes unstable, as bypass valve A may not control coolant flow across its intended range.