EGR Sensor : Diagram, Working, Causes, Symptoms,Fault Codes & Its Applications

Vehicle manufacturers around the world have been forced to reduce exhaust emissions. This applies to both petrol & diesel engines with a better focus on diesel because of the higher range of NOX pollutants they produce into the environment. The EGR system helps in moderating NOX emissions generated within the combustion chamber. Whenever the combustion temperature of the engine is high by establishing an amount of its exhaust gas into the intake air then the temperature will be reduced. In diesel engines, the EGR system becomes very active whenever the exhaust gas achieves 450 ̊C while it is 650 ̊C within petrol applications. This article briefly explains the EGR sensor, its working, and its applications.

What is an EGR Sensor?

The EGR (Exhaust Gas Recirculation) sensor detects the movement of the exhaust gas flow throughout the EGR valve in the vehicle. The function of the EGR sensor is to maintain proper emissions on vehicles by monitoring the EGR valve position & allowing more precise EGR flow rate control. After that, the computer system changes engine performance to declare allowable emissions. These sensors are associated commonly with automotive applications and are also appropriate for use in agricultural, construction & industrial equipment. The housing of the EGR sensor needs high thermal stability, strength necessities and wear resistance at prominent temperatures.

EGR Sensor
EGR Sensor

How Does EGR Sensor Work?

The EGR sensor is a significant component within an exhaust system of the vehicle that observes the flow & composition of the exhaust gases which are recirculated back into the vehicle engine. So this helps the ECU (engine control unit) to adjust the operation of the EGR valve, which in turn assists in reducing emissions as well as improving the efficiency of fuel. EGR is mainly used in cars for two reasons like; higher efficiency & lower pollutant emission.

Exhaust Gas Recirculation System Diagram

The EGR system is one of numerous vehicle emission control systems that helps reduce the quantity of NOx (nitrogen oxides) within the exhaust gases. Generally, Nitrogen oxides can be formed in the combustion process in the engine cylinders. Although NOx formation can be enhanced severely at higher combustion temperatures which is above 1600 °C (or) 2912 °F.

Higher combustion temperatures are very dangerous to the engine which causes effects like detonation or pre-ignition when the fuel or air mixture ignites within the cylinders from extreme heat. As it occurs at the incorrect time, the detonation includes strain on the vehicle’s engine components before the sparkle. So, prolonged explosion damages the pistons, valves & many other parts. The EGR system decreases the combustion temperature by redirecting a small part of the exhaust gases which goes back to the intake manifold. These gases are no longer flammable, so diluting the intake air by exhaust gases will make the fuel or air charge less flammable.

Exhaust Gas Recirculation System Diagram
Exhaust Gas Recirculation System Diagram

How the Engine Computer Controls the Flow of the EGR System?

The engine computer helps in opening or closing the EGR valve to control the flow in the EGR system. Here, the EGR valve is used to connect the exhaust manifold and the intake manifold. This valve is generally closed, so there is no EGR flow whenever the engine is cold, inactive, or through hard acceleration. In steady cruising, the flow of EGR is at its peak in moderate load. The EGR valve in some vehicles is operated through a vacuum actuator because modern cars contain an electric EGR valve through a step motor.


How the Flow of the EGR System is Monitored?

The engine computer tests the EGR system periodically with other emission control systems. So if the flow is less or more than expected, then PCM will detect a fault & enable the light of the Check Engine above the instrument panel.

There are different methods to monitor the flow of EGR. An EGR temperature sensor is installed in some cars in the intake element of the EGR system. When the EGR valve unlocks, the temperature at the intake side will increase from the hot exhaust gases.

Modern cars utilize an electric EGR valve but some vehicles also have an EGR cooler. So the EGR flow is controlled by PCM by opening (or) closing the EGR valve through a step motor. The EGR flow is monitored by the MAP sensor, MAF sensor & the fuel or air ratio sensor.

Symptoms of a Bad EGR Sensor

A faulty EGR sensor can cause many problems with the EGR system flow & operation which leads to performance issues like power reduction, vehicle emissions, decreased acceleration & fuel efficiency.

  • The car engine has a rough idle.
  • Poor performance of the vehicle.
  • Fuel consumption can be increased.
  • Your car regularly stops when idling.
  • You can get a fuel smell.
  • The engine management light in the car stays on.
  • The car generates more emissions.
  • You can hear knocking noises which are coming from the car engine.
  • It can lead to an obvious decline in engine performance.
  • You may experience a hesitation while starting your car.
  • Sluggish acceleration or a lack of power while driving uphill.


The causes of bad EGR sensors are discussed below.

  • Bad fuel can lead to decreased engine performance, improved emissions & potential harm to the sensor.
  • Ignoring frequent maintenance of your car can lead to EGR failure.
  • Over time carbon deposits can build up in the EGR valve & its linked components can restrict the exhaust gas flow & impact the functionality of the valve negatively.
  • A bad EGR valve can stop the valve from properly opening (or) closing.
  • Manufacturing defects cause EGR valve problems so that the valve in the beginning may be faulty leading to premature failure or poor performance.
  • Exposure to severe operating conditions like; excessive dust, extended periods of heavy load, and high temperatures can hasten the wear & tear on an EGR valve.
  • All these operating conditions can lead to speed-up carbon buildup & stress on the EGR valve components to cause premature failure potentially.
  • Thus, to reduce causes caused by EGR valves, make sure to utilize reputable fuel sources and follow the vehicle manufacturer’s recommendations. So regular maintenance by changing the oil & replacing or cleaning the EGR according to the maintenance plan can help prevent issues & extend the valve’s life.

How to Troubleshoot EGR Sensor?

The steps involved in troubleshooting an EGR include the following.

  • Ensure that all electrical connections & vacuum lines are properly connected & positioned.
    A vacuum gauge needs to be used to verify the vacuum supply pipe for vacuum at 2000 to 2500 rpm. At normal operating temperatures, no vacuum would advise a loose hose, a faulty or blocked ported vacuum switch, or a faulty solenoid vacuum pump or amplifier.
  • Verify the vacuum solenoid when the engine is running. If the solenoid does not unlock when it is energized, then it will stuck within the open (or) closed position otherwise has a loose wire (or) bad GND, and then the EGR operation will be changed.
  • Check the valve stem movement at 1500 – 2000 rpm and it must move if the EGR valve is correctly working.
  • Directly apply vacuum to the EGR valve with either a scan tool or hand vacuum pump based on the kind of EGR valve.
  • Take out the EGR valve & verify for carbon build-up.
  • Examine the EGR tube within the manifold for cleaning & clogging if necessary.

How to Replace EGR?

The EGR can be replaced based on the following steps.

  • First, need to remove the cover of the vehicle engine.
  • After that, untie the electrical cable above the valve & take out the electrical connections & vacuum lines by verifying for signs of harm.
  • Eliminate the fastening screws & ensure the valve for injury, carbon build-up or corrosion.
  • Thoroughly clean the mounting surface of the EGR valve & fit the new valve as well as the gasket.
  • Take away any movable carbon from the supply port of EGR also
  • Assemble the EGR valve through the bolt holes, and gasket & reconnect to the housing.
  • Stiffen all fasteners toward the suggested torque settings.
  • When tightly seated then reconnect the vacuum lines & electrical connections.
  • At last, utilize a diagnostic scan tool for resetting the engine management light & verify for any other faults. Now many cars need the EGR valve to be rearranged in adaptations. So this allows simply the ECU to study the stop position on the open & closed points.

EGR Fault Codes

The common fault codes of EGR valves include the following.

P0400 – Malfunction of EGR flow.
P0401 – Detection of insufficient EGR flow.
P0402 – Excessive flow of EGR.
P0403 – Malfunction of EGR circuit.
P0404 – Range or performance of EGR circuit.
P0405 – A circuit of the EGR sensor is low.
P0406 – A circuit of the EGR sensor is high.
P0407 – B circuit of the EGR sensor is low.
P0408 – B circuit of the EGR sensor is high.
P1403 – Low EGR solenoid.
P1404 – Pintle error of closed valve in EGR system.
P1405 – Solenoid high for EGR
P1406 – Pintle position error for EGR system.

Advantages & Disadvantages

The advantages of the EGR sensor include the following.

  • EGR system helps in reducing nitrogen oxide emissions by recirculating a part of the exhaust gases in the engine back into the combustion chamber.
  • It can lower the combustion temperature by decreasing the concentration of intake oxygen which can enhance fuel efficiency.
  • It helps in decreasing detonation or engine knock by decreasing the peak combustion temperatures.
  • EGR decreases heat dissipation to the surfaces of the combustion chamber which protects more thermal energy to convert into mechanical work throughout the expansion stroke.
  • It allows vehicle engines to attain a balance between emissions reduction & performance for supporting sustainable transport solutions.
  • It helps in reducing the development of particulate matter that contributes to air pollution & health issues.
  • When EGR slightly decreases combustion then its effects can be compensated frequently for by progressing spark timing & the performance of maintaining the optimal engine.
  • It can be combined through other emissions control technologies like catalytic converters for reducing unsafe pollutants.

The disadvantages of EGR sensors include the following.

  • EGR system reduces engine power as well as responsiveness, particularly at lower RPMs.
  • It adds complexity to the vehicle’s engine, which can lead to reliability issues & potential maintenance.
  • These systems can lead to carbon buildup within the valves & intake manifold which affects potentially engine performance.
  • Extreme utilization of EGR can lead to decreased power output because it lowers the incoming air-fuel mixture density, then it can affect the overall performance & responsiveness of the engine.
  • Excessive EGR causes partial combustion which can lead to misfires, reduced engine efficiency & rough idling.
  • EGR can build up carbon deposits eventually which leads to EGR valve clogging & related components. So this affects the reliability & replacement of the system.
  • The incorporation of EGR systems can add complexity to the vehicle’s engine which needs additional components like valves, control systems & sensors. This complexity increases the costs & maintenance requirements of manufacturing.
  • EGR introduces hot exhaust gases into the intake system, which can enhance the intake air temperature & potentially impact the efficiency of the cooling system.

EGR Sensor Applications

The applications of EGR sensors include the following.

  • An EGR sensor is used to decrease the nitrogen oxide emission within the exhaust gas
  • These sensors are associated normally with automotive applications which are also appropriate to utilize within agricultural, construction & industrial equipment.
  • EGR is a very effective strategy that controls emissions of NOx from diesel engines without enhancing fuel consumption.
  • It is a significant control component of the vehicle engine which is located on the intake pipe. The main function of this is to control the sum of exhaust gas coming into the intake manifold thus, a certain quantity of exhaust gas supplies into the intake manifold mainly for recirculation.

Thus, this is an overview of the EGR sensor, its working, advantages, disadvantages, and its applications. The EGR sensor in an exhaust system of the vehicle is a significant component that monitors the exhaust gas flow & composition which is being recirculated back into the car engine. So this helps the ECU to regulate the operation of the EGR valve, which in turn assists in decreasing emissions and also enhances fuel efficiency. These sensors are located near the EGR valve because the exhaust gas hose should be connected to the EGR sensor & the valve. The common causes of EGR sensor failure are because of shorts, opens (or) intermittent signals. Here is a question for you, what is an engine knock sensor?