What it means
The position sensor on the coolant bypass valve A returns no usable signal. Closed-loop control of bypass position is lost.
At a glance
- Usually lights the check-engine light
How it works
Coolant bypass valve A changes coolant routing, and its position sensor reports how far the valve has moved so the module can control temperature. P26A4 means the sensor circuit does not provide a usable position signal, leaving the module unable to confirm valve A's position.
Common causes
Most likely first.
- Open sensor element
- Corroded sensor connector
Symptoms
- Check-engine light
- Engine temperature may fluctuate
- Heating or warm-up may be affected
How to diagnose it
- Check freeze-frame data and live valve command and position feedback to see whether the sensor signal is absent, fixed, or erratic.
- Inspect the valve A sensor connector and wiring for looseness, corrosion, water intrusion, or damaged insulation.
- Check sensor supply, ground, and signal at the connector using the wiring diagram and manufacturer's specification.
- With power isolated as specified, test continuity of the sensor circuit and check for shorts between its wires.
- If wiring and circuit feeds pass, test the valve A position sensor and valve movement according to the manufacturer's procedure.
Common fixes
- Reconnect a loose sensor connector and secure the wiring.
- Repair corroded terminals or damaged sensor wiring.
- Replace the position sensor if it fails the specified circuit or signal test.
- Replace bypass valve A if the sensor is integral and the assembly fails testing.
Can I keep driving?
Drive only while monitoring the temperature gauge and stop if the engine overheats, because the module cannot verify bypass valve A's position. Heating and warm-up may also be erratic, so avoid long trips until the fault is diagnosed.
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.