What it means
Voltage on the fourth coolant bypass valve control line is above 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 an electrically controlled valve that routes 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 is above the expected range, potentially preventing the valve from being controlled properly.
Common causes
Most likely first.
- Control wire shorted to B+
- Open 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
- Review freeze-frame data and scan-tool commands or feedback for bypass valve D to determine when the high-circuit fault occurred and whether it is active.
- With the engine cool, inspect valve D's connector and harness for chafing, moisture, corrosion, loose pins, or pin push-back.
- Check whether valve D's solenoid coil is open using the manufacturer's specified test and compare the result with its specification.
- With the circuit safely isolated as specified by the manufacturer, test the valve D control wire for a short to battery voltage and inspect connector contact quality.
- If the fault is intermittent, monitor the circuit while gently moving the valve D harness and connector, then check module-side control only after the wiring and coil pass.
Common fixes
- Clean and secure the valve D connector and repair damaged seals or pushed-back terminals.
- Repair chafed valve D wiring that is shorted to battery voltage.
- Replace the open-circuit valve D solenoid if it fails the manufacturer's test.
- Repair the valve D control circuit or module connection if testing identifies the fault there.
Can I keep driving?
If the temperature remains normal, a short, gentle drive to a repair location may be reasonable, but avoid demanding use and monitor the gauge. Stop safely if the engine overheats or temperature becomes unstable, since valve D may not route coolant correctly.
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.