What it means
The vacuum reservoir control circuit reads stuck low — short to ground or low-side driver stuck on. The actuator may be energised continuously when it should be off.
At a glance
- Usually lights the check-engine light
How it works
The vacuum reservoir control circuit operates a valve or pump that helps maintain stored vacuum for systems such as brake assist or HVAC controls. This code sets when the controller detects the circuit voltage staying below its expected level, often because the control wire is grounded and the actuator may remain energised when it should be off.
Common causes
Most likely first.
- Control wire shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- Check-engine light
- Vacuum-operated functions may work inconsistently
- Brake pedal may feel harder if brake-assist vacuum is affected
How to diagnose it
- Review freeze-frame data and available actuator command or vacuum readings to see whether the low circuit state coincides with a control command.
- Inspect the valve or pump connector and harness for corrosion, loose pins, or insulation worn through against ground.
- Check whether the vacuum actuator is being commanded continuously and note whether vacuum-operated functions behave abnormally.
- Use the wiring diagram to test the control wire for a short to ground and check connector contact quality.
- If no wiring fault is found, test the actuator and controller output for a stuck-on condition against the manufacturer’s specification.
Common fixes
- Repair chafed control-wire insulation that is contacting ground.
- Clean or replace corroded terminals and restore a secure connector fit.
- Replace a faulty valve or pump if its electrical load is outside specification.
- Repair the controller driver only after ruling out wiring and actuator faults.
Can I keep driving?
If the brake pedal becomes hard or brake assist is reduced, stop driving and arrange recovery. Otherwise, drive cautiously only as far as needed for repair, since an unintended continuously energised actuator can deplete or disrupt vacuum for supported systems.
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.