1991 Volvo 940 EGR Vacuum Control Solenoid Replacement Cost

The exhaust gas recirculation (EGR) vacuum control solenoid is very aptly named in that it controls the EGR valve with engine vacuum. For EGR valve to help degrease harmful emissions, it opens up to allow exhaust gas from the engine to go back through the intake manifold to be reburned. This prevents unburned fuel and harmful contaminants from reaching the atmosphere. This valve cannot stay open all the time, so it needs a component to open and close it when needed. This component is called the EGR vacuum control solenoid.

When the engine control module (ECM) wants the EGR valve to open or close, it will either energize or ground the solenoid so that it opens or closes. When the solenoid is either opened or closed, vacuum will be allowed to flow, but the other position will block the flow of vacuum. Depending on the vehicle, when vacuum is allowed to flow, it will actuate the EGR valve, allowing exhaust gases to pass through the EGR valve and into the intake manifold.

As with any EGR issue, the most common symptoms noticed when the EGR vacuum control solenoid fails are rough idling, hesitation accelerating from a stop, lack of engine power, misfires, and, of course, illumination of the dreaded check engine light. If failure occurs with the EGR valve stuck open, the vehicle will suffer reduced gas mileage and decreased catalytic converter operations, not to mention the check engine light. Hesitation from a stop may also be accompanied by stalling or very low engine speed when slowing the vehicle down, especially from highway speeds. The vehicle may also hesitate for a short or extended time, then accelerate quickly as if the accelerator pedal were pressed to the floor.

Anytime the check engine light comes on, especially if flashing, the vehicle should be seen by a professional, or scanned to identify the on-board diagnostic trouble codes stored in the engine control module. The check engine light should not be ignored, especially if the issue pertains to the EGR system. Not only will a faulty EGR system lead to poor gas mileage and the mentioned symptoms, but it can ultimately lead to failure of the vehicle to start and run.

Since vacuum pressure control solenoids are simple, have only one real moving part, and are primarily electronic components, they tend to last quite a while. Time will take its toll on these components, especially since the small ports for vacuum lines are apt to breakage when they have become brittle. Expect most solenoids, of any type, to have a long service life, but they are known to fail by internal leaking, sticking, or physical degradation and breakage.

Diagnosing a vacuum control solenoid is simple, and requires no tools. A technician with tools at their disposal will likely use a vacuum pump with a gauge and a multimeter to backprobe. Simply done, the solenoid can be disconnected electrically, vacuum can be pulled on the vacuum port, and the pins can be attached to a twelve volt power source. The solenoid should click when connected, and if the vacuum did not drop before connecting power, the vacuum gauge should jump to zero. This allows the technician to understand that the solenoid is moving both directions and the valve within the solenoid is holding vacuum and releasing when requested.

If the valve failed to hold or release vacuum or the solenoid failed to click on and off, replacement is necessary. To perform this repair, the solenoid would be separated from the vacuum lines first, then the electrical connection, and finally mounting hardware can be removed to release the EGR vacuum control solenoid from the vehicle. Replacement is as simple is removal, and the vacuum lines should be tested to ensure serviceability.

Especially if the vacuum control solenoid tests operational, we recommend checking for vacuum and exhaust leaks when the EGR system is operating incorrectly. This is easy to do, quick, and may find the solution before any real diagnostic work must take place. A vacuum hose or loose fitting can cause many EGR issues.

The EGR system is nearly as hot as the exhaust system, especially if the engine has been running under heavy load or high engine speed. Wait at least thirty minutes to one hour before servicing the system, or just ensure the portion you are servicing is cool to the touch before proceeding. All systems do not use vacuum modulation for the EGR valve, and those will not have a vacuum control solenoid either.

The EGR vacuum control solenoid is straightforward to diagnose and replace. As long as the EGR system and computerized automotive circuits are understood, this can be done by anyone with a multimeter and a little time to spare. Ensuring proper workplace safety is vital, especially when working with a hot system, and the DIY mechanic should understand the specific range of vacuum and voltage the vacuum control solenoid is meant to use.