What it means
The control circuit that drives the vacuum reservoir control valve (or vacuum pump motor) is open. The ECM cannot energise the actuator, so vacuum is no longer maintained on demand and consumers like brake booster, EGR or HVAC dampers may run out of vacuum.
At a glance
- Usually lights the check-engine light
How it works
The vacuum reservoir control circuit lets the engine controller operate a valve or pump that maintains stored vacuum for supported systems. This code sets when the circuit is open and the controller cannot energise that actuator, so vacuum-dependent functions may lose assistance or operate inconsistently.
Common causes
Most likely first.
- Open control wire
- Failed driver in the control module
- Pin pushed back out of connector body
Symptoms
- Check-engine light
- Vacuum-operated functions, such as HVAC controls, may work inconsistently
- Brake pedal may feel harder if brake-assist vacuum is affected
How to diagnose it
- Check freeze-frame data and any available actuator command or vacuum data to identify when the control circuit failed.
- Inspect the reservoir valve or pump connector for a pushed-back pin, corrosion, or a loose fit.
- Trace the control wire between the actuator and controller for breaks, chafing, or heat damage.
- With power isolated as specified by the manufacturer, test the control wire for continuity and shorts to ground or power.
- If the wiring and connector are sound, check the actuator coil or motor and then the controller output against the manufacturer’s specification.
Common fixes
- Reseat a pushed-back terminal and secure the connector.
- Repair an open or damaged control wire.
- Replace the vacuum reservoir valve or pump if its coil or motor is open.
- Repair the control module only after confirming the circuit and actuator are sound.
Can I keep driving?
If the brake pedal becomes hard or brake assist seems reduced, stop driving and arrange recovery; do not rely on the vehicle until the cause is addressed. If braking feels normal, limit the trip to a safe repair location and watch for changes in brake effort or HVAC operation.
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.