What it means
The fourth actuator supply rail is below the expected voltage. 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
Actuator supply rail D powers a group of controlled actuators, and the module checks that the rail stays within its expected voltage range. This low-circuit code sets when the supply voltage falls below that range, which can disrupt the actuators and trigger related faults.
Common causes
Most likely first.
- Load on the rail shorted to ground
- Battery condition causes voltage to drop
- Connector pins corroded - high contact resistance
Symptoms
- Actuator-related warning light or check-engine light may come on
- Some engine or vehicle functions may be reduced or unavailable
How to diagnose it
- Use a scan tool to save freeze-frame data and compare actuator-related codes to see which functions were affected when rail D voltage dropped.
- Check battery condition, charging behavior, and main power connections for a low supply that could pull the rail down.
- Inspect the rail D fuse, relay, harness, and powered actuator connectors for corrosion, loose terminals, heat damage, or a short to ground.
- With the wiring diagram, measure rail D voltage at the fuse, relay output, and affected actuator feeds under the conditions specified by the manufacturer.
- If the supply and connections check out, isolate the loads as directed by the manufacturer to find an actuator or branch shorting the rail low.
Common fixes
- Repair a rail D wire shorted to ground.
- Clean or repair corroded or loose terminals in the rail D supply path.
- Replace a faulty battery or repair the charging system if testing shows it is causing low system voltage.
- Replace an actuator only after confirming that it is pulling rail D voltage down.
Can I keep driving?
A low rail can make engine or vehicle actuators work incorrectly, causing reduced power or other functions to become unavailable. Limit driving if running or control problems appear, and stop if the vehicle becomes unsafe to operate.
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.