1. Home
  2. Articles
  3. Symptoms of a Bad or Failing EGR Vacuum Modulator

Symptoms of a Bad or Failing EGR Vacuum Modulator

EGR vacuum modulator

The EGR vacuum modulator is a component found on some EGR systems. It controls the flow of the EGR system by using a vacuum operated diaphragm to increase or decrease EGR flow. When the vacuum is high, combustion temperatures and airflow are naturally lower so the diaphragm will close and restrict flow, when vacuum is low airflow and combustion temperatures are higher, so EGR flow must be increased.

For vehicles equipped with them, the EGR vacuum modulator is one of the most important components of the EGR system. Any issues with it can cause the system to malfunction, which can lead to increased emissions and other problems. Usually a bad or failing EGR vacuum modulator will produce a few symptoms that can alert the driver of a potential problem that should be serviced.

1. Engine performance issues

One of the first problems of a potential issue with the EGR vacuum modulator is engine performance issues. If the EGR vacuum modulator diaphragm tears or leaks it will disable the EGR system and may cause a vacuum leak. An excessively large vacuum leak can result in engine performance issues such as a decrease in power, acceleration, and fuel economy.

2. Check Engine Light comes on

Another symptom of a potential problem with the EGR vacuum modulator is an illuminated Check Engine Light. If the computer detects a problem with the EGR vacuum modulator signal or circuit it will set off the Check Engine Light to alert the driver of an issue. The Check Engine Light can also be activated for a variety of other reasons, so having the vehicle scanned for trouble codes is highly recommended.

3. Failed emissions test

Another symptom of a potential problem with the EGR vacuum modulator is a failed emissions test. Sometimes the EGR vacuum modulator can fail, and not set off the Check Engine Light. This will result in increased NOx emissions, which can cause the vehicle to fail an emissions test if the levels climb too high. This is particularly important for states that require emissions testing for all of their registered vehicles.

While the EGR systems on newer vehicles are being controlled by a wide variety of other methods, EGR vacuum modulators are still commonly found on many road going cars and trucks. They serve an important purpose in the overall functionality of the EGR system and when they fail can cause an increase in emissions. If you suspect that your vehicle’s EGR vacuum modulator may be having an issue, have the vehicle inspected by a professional technician, such as one from YourMechanic to determine if the component should be replaced.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Still not sure about your car's issue?
Diagnose your car
What kind of issue are you experiencing?
Brakes are squeaking
Car is not starting
Car is overheating
Car is shaking (vibrating)
Fluids are leaking
Heating and A/C
Smoke or steam is coming out of the car
Warning light is on
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
How to Avoid Back Pain in a Car
If you have back problems, sitting in a car for an extended period of time can be excruciating. Even without back problems, you could experience discomfort and soreness from...
P0291OBD-II Trouble Code: Cylinder 11 Injector Circuit Low
P0291 code definition When your vehicle’s PCM registers the P0291 code, it means that a voltage reading came from the fuel injector circuit – for cylinder number 11’s fuel injector –...

Related questions

Q: Changed heads. Engine runs great until I put it in gear, then I have no power from transmission, shifts hard, and breaks are hard.

Hey there. Given that you performed a fair amount of engine work and have no doubts with the battery out of the car, it is possible that the throttle position sensor and engine management have lost their "pairing" values and...

Q: Replaced downstream o2 sensor, check engine light related to that sensor. What do i do?

Claimed by John Hege

Q: Check engine light came while driving. Is this a serious problem? car seems to be running fine. 2004 Hyundai SantaFe

Hello - the Enhaust Gas Recirculation - EGR - system reduces emissions by recirculating exhaust gases that are not completely burned back through the engine. This is done in a timed manner under certain conditions. If this system is not...