What it means
Voltage on the fourth coolant bypass valve control line is below the expected window. 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
Coolant bypass valve D is controlled electrically to route coolant through a particular part of the cooling system. The control module monitors voltage on valve D's control circuit; this code sets when voltage falls below the expected range, which may leave the valve unable to follow commands.
Common causes
Most likely first.
- Control wire shorted to ground
- Internal short in solenoid coil
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light may be on
- Engine may take longer to warm up
- Coolant temperature may fluctuate
How to diagnose it
- Check freeze-frame data and scan-tool commands or feedback for bypass valve D to see when the low-circuit fault occurred and whether it is present now.
- With the engine cool, inspect valve D's connector and harness for chafing, a wire shorted to ground, moisture, corrosion, or loose and pushed-back pins.
- Test valve D's solenoid coil for an internal short using the manufacturer's procedure and compare the result with its specification.
- With the circuit safely isolated, check the valve D control wire for a short to ground and inspect connector contacts for high resistance.
- If the fault is intermittent, monitor the circuit while gently moving the valve D harness, then check module-side control after the wiring and coil have passed.
Common fixes
- Clean and secure the valve D connector and repair damaged seals or terminals.
- Repair the valve D control wire if it is shorted to ground or chafed.
- Replace the valve D solenoid if testing confirms an internal short.
- Repair a confirmed high-resistance connection or module-side circuit fault.
Can I keep driving?
If the engine temperature remains normal, drive only as needed and watch the gauge closely. Stop if it overheats or temperature becomes unstable, because valve D may not control coolant flow correctly and cabin heat may be affected.
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.