What is the EGR Vacuum Modulator all about?

Your vehicle’s exhaust gas recirculation (EGR) system is used to reduce your engine’s emissions by lowering the combustion chamber temperature. This produces less nitrous oxides, and burns pollutants contained in the exhaust gas that are reintroduced into the intake manifold. If the EGR valve opens and allows exhaust gases into the intake, the engine runs more smoothly and efficiently. However, this is not the case at idle, when the engine needs the most vacuum for proper operation. If the EGR valve opens at idle, you can experience a rough idle and possibly a knock. Engine power is negatively affected at low RPM’s. Engineers implemented a control that closes the EGR valve when the engine is running at lower RPM’s. The engine produces lower vacuum at lower engine speeds, so it’s natural that the control is modulated by the engine’s own vacuum. The EGR vacuum modulator is a diaphragm that closes when the engine vacuum drops to idle, and opens as soon as the vacuum increases. It’s also known as a vacuum modulated valve. If the EGR vacuum modulator is leaking vacuum, is blocked internally, or is leaking, the Check Engine light will come on and the engine may start to knock.

Keep in mind:

• The EGR system assists in reducing engine emissions. An improperly operating EGR system can cause a smog test failure.
  • Vacuum hoses become brittle over time. Take precautions to not damage the vacuum hoses when working on the EGR system.

How it's done:

• The EGR vacuum modulator is verified that it needs to be replaced. The engine top trim cover is removed to access the modulator.
• The defective EGR vacuum modulator is removed from the bracket near the EGR valve and is disconnected.
• The new EGR vacuum modulator is installed and reconnected.
• The engine is started and the EGR vacuum modulator is tested for computer codes and operation.
• The vehicle is road tested to ensure proper operation of the EGR vacuum modulator.

Our recommendation:

The EGR vacuum modulator does not have a replacement interval. It will likely need replacement at some time because it does contain a filter. It can be inspected any time a vacuum test needs to be performed on the engine vacuum. If the EGR vacuum modulator is deemed to be faulty, you will need to have it replaced by one of our expert technicians.

What common symptoms indicate you may need to replace the EGR Vacuum Modulator?

• Check Engine light is on
• Engine knock at idle
• Engine idles rough

How important is this service?

The EGR system partly controls your vehicle’s emissions, and a faulty EGR vacuum modulator can cause your car to fail a smog test. In addition, your vehicle may not idle, or may knock at idle. It is recommended to replace a faulty EGR vacuum modulator as soon as possible.