What it means
The supply voltage to actuator group B (e.g. solenoids, valves driven by ECU) is below the calibrated threshold. The affected actuators may be slow or unable to switch.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
Actuator supply voltage B powers a group of ECU-driven actuators, and the module monitors whether that rail stays above its operating threshold. This code sets when supply B is too low, so solenoids or valves may switch slowly or fail to switch.
Common causes
Most likely first.
- Faulty supply relay
- Wire shorted to ground
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light
- One or more actuators may operate slowly or not switch
How to diagnose it
- Record freeze-frame data and use live data to check actuator supply B when the fault is present, noting whether low voltage coincides with an actuator command.
- Inspect the supply B relay, fuse, connectors, and ground points for looseness, corrosion, heat damage, or water entry.
- Trace the B supply wiring for a short to ground or damaged insulation, paying attention to connectors with corroded or loose pins.
- Measure voltage drop across the relay, connectors, and supply path under load, comparing results with the manufacturer's specification.
- If wiring and connections are sound, test the relay and charging supply, then check the module's B rail monitoring using the manufacturer's procedure.
Common fixes
- Clean and secure corroded or loose actuator supply B connector terminals.
- Replace a faulty supply B relay if it cannot maintain the feed under load.
- Repair a B supply wire shorted to ground or damaged by chafing.
- Repair or replace a damaged supply connector or fuse connection causing excessive resistance.
Can I keep driving?
One or more actuators may respond slowly or stop switching, and engine performance or emissions can worsen. Avoid demanding driving if the engine runs poorly, and have the low supply checked soon.
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.