What it means
The bypass valve A position sensor signal is above the upper diagnostic threshold. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.
At a glance
- Usually lights the check-engine light
How it works
The position sensor on coolant bypass valve A reports valve movement to the control module. This code sets when its signal rises above the module's upper diagnostic threshold, so the module cannot trust the reported position.
Common causes
Most likely first.
- Open sensor element
- Signal wire shorted to the 5 V reference
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light
- Engine temperature may fluctuate
- Heating or warm-up may be affected
How to diagnose it
- Capture freeze-frame data and inspect live data for bypass valve A's position signal, checking whether it is high continuously or only under particular conditions.
- Inspect the sensor connector and harness for an open circuit, corrosion, loose pins, or a signal wire chafed against the 5 V reference.
- With the code active, gently move the harness near valve A while watching live data for a change in the high reading.
- Check the sensor supply, ground, and signal wires for an open or short to the 5 V reference, following the wiring information and manufacturer's specification.
- If the wiring is intact, test the position sensor for an open sensor element or incorrect output.
Common fixes
- Reseat the sensor connector and repair corroded or damaged terminals.
- Repair an open signal wire or a signal wire shorted to the 5 V reference.
- Restore a poor sensor ground or other faulty circuit connection.
- Replace the bypass valve A position sensor if its element is open or its output remains high with sound wiring.
Can I keep driving?
If engine temperature stays normal, limit driving to short, gentle trips and keep the temperature gauge in view. Stop if it rises above normal or the engine overheats, because the module may be unable to regulate coolant flow using valve A's position feedback.
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.