What it means
During cold start, the engine coolant bypass valve D is stuck in the open position. Coolant bypasses the warm-up loop.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Coolant bypass valve D routes coolant through a path used to control engine warm-up. During a cold start, the control module checks whether the valve reaches the commanded position; this code sets when it remains open and coolant does not stay in the intended warm-up loop.
Common causes
Most likely first.
- Valve stuck in open position
- Actuator failed
- Carbon or debris buildup preventing free movement
Symptoms
- Check-engine light
- Slow engine warm-up
- Weak cabin heat in cold weather
- Temperature gauge may take longer to rise
How to diagnose it
- Use a scan tool to record freeze-frame data and compare coolant temperature from a cold start with ambient temperature to confirm the slow warm-up condition.
- Inspect valve D and its connector and wiring for loose connections, corrosion, damage, or coolant contamination.
- Check live data for the commanded and reported positions of valve D during a cold start, if the vehicle provides those values.
- With the manufacturer's test procedure, check whether the valve actuator responds when commanded through its operating range.
- If the actuator responds but coolant still follows the wrong path, inspect the valve for debris or sticking and verify coolant routing against the vehicle's service information.
Common fixes
- Repair a loose, corroded, or damaged connector or wiring at coolant bypass valve D.
- Remove debris that is preventing valve D from closing or moving freely, if the manufacturer's procedure permits cleaning.
- Replace coolant bypass valve D if it is mechanically stuck open.
- Replace the valve actuator if it fails the commanded-operation test.
Can I keep driving?
You can usually drive gently for a short trip if the temperature gauge stays normal, but expect slow warm-up and weak cabin heat. Stop if an engine temperature warning appears, since inadequate coolant control can lead to overheating.
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.