Even though diesel engines are more efficient, they are notorious for releasing more noxious waste to the environment than gasoline-powered ICEs.Manufacturers have made many efforts to reduce emissions and make engines run cleaner.
One important invention is the Exhaust Gas Recirculation (EGR) system. While common in diesel engines, its efficiency has seen it touch base with some petrol engines trying to get cleaner and hit tighter emission regulations.
What Does EGR Do?
Any exhaust gas recirculation system pumps back gases from the exhaust manifold into the engine intake with the goal of reducing combustion chamber temperatures.
The goal is to keep temperatures lower than 2370 degrees, the figure beyond which combustion yields more NOx emissions. The system consists of intake ports, sensors, an EGR cooler, and an EGR valve.
What Does an EGR Valve Do?
The EGR valve is the main component of the entire system. It controls how exhaust gets recirculated at any given time.
It either runs on a vacuum effect or has an electric step motor for precise control. The engine load determines how much the valve will open hence maintaining tight control over how much exhaust gases make it back to the intake manifold.
An EGR valve will start working once the engine is at operational temperature and you are driving at speed since it’s at this time combustion temperatures could shoot above 2370 degrees.
It will close as soon as you slow down or you stop the engine.
Why Do EGR Valves Fail So Often?
Since the valve controls exhaust gas flow, it is in contact with unfiltered exhaust gases. All that soot that gets stuck in the Diesel Particulate Filter or the Catalytic Converter is still in the exhaust gases.
Over time, the solids in the exhaust accumulate on the valve. This will either partially or fully block it rendering the whole system inefficient.
Diesel EGR systems get dirtier faster than those on a petrol engine. Also, expect more gunk if you use low-quality diesel without cleaning additives.
Signs that You Have a Bad or Clogged EGR Valve
Since you can’t keep inspecting your EGR valve as often as you check your coolant levels or oil levels, you have to know the symptoms a faulty valve brings. Here are the most common signs to look out for.
Your Check Engine Light Will Pop Up
Just as there are tons of sensors monitoring other aspects of your powertrain, you also have sensors checking on your EGR valve’s performance.
If it is clogged, stuck closed or stuck open, the operational parameters from these sensors will be off spec. This will in turn trigger the check engine light.
Some of the most common EGR valve and system error codes include:
| Fault Code | Meaning | Fault Type | Cause |
| P0401 | EGR Flow Insufficient | Mechanical | Blanking plate or EGR valve stuck closed |
| P0402 | EGR Flow Excessive | Mechanical | EGR valve stuck open or jammed by carbon buildup/ bent shaft |
| P0403 | EGR Circuit Malfunction | Electronic | Solenoid circuit problem. Low voltage at EGR solenoid |
| P0404 | Exhaust Gas Recirculation Circuit Performance | Electronic | Solenoid circuit malfunction. High voltage at EGR solenoid |
| P0405 | EGR Sensor A Circuit Low | Electronic | Malfunctioning solenoid position sensor. Sensor detects EGR closed more often than it should be |
| P0406 | EGR Sensor A Circuit High | Electronic | Malfunctioning solenoid position sensor. Sensor detects EGR open more often than it should be |
| P0407 | EGR Sensor B Circuit Low | Electronic | Position sensor for Solenoid malfunctioning. Sensor detects EGR closed more often than it should be |
| P0408 | EGR Sensor B Circuit High | Electronic | Position sensor for Solenoid malfunctioning. Sensor detects EGR open more often than it should be |
| P1404 | IAT B Circuit Malfunction or EGR Closed Position Performance | Electronic | EGR possibly stuck open |
Apart from getting EGR-specific error codes, you might get other related errors. Common relations could include:
- Misfires
- Rich or lean fue/air mix
Your Engine Will Be Weak and Sluggish
Since the PCM accounts for EGR gasses when creating the fuel mix ratio, underperformance from the valve will throw off strict calculations.
The result is an inefficient engine that doesn’t produce as much power as it should under calculated scenarios.
Your vehicle will accelerate slower and you will have to sink the pedal further into the metal to get the performance you need.
If the EGR valve is stuck open, your vehicle will be weaker at low speed. It will feel weaker at high speeds if your valve is stuck close.
You Will Idle Rough
Normally, an EGR valve starts closed and stays closed until the engine has warmed up. This allows your engine to consume fresh oxygen-rich air which is perfect for smooth idling.
If the valve is stuck open, it will introduce the exhaust gas compromise earlier than the engine can handle reducing power output and preventing the motor from warming up fast.
This reduces the power from your engine and will make it idle rough. Your engine should resume idling smoothly as soon as it warms up if this is the problem.
In cases where the problem is very serious, the engine will be so weak at idle and low speeds it will stall without a load or as soon as you add a small load like the AC or slipping into gear.
A Strong Exhaust Smell
The EGR was designed to reduce NOx. And it does such a good job about it to the extent that we’ve forgotten how NOx emissions smell.
If the system fails, your vehicle will release more of these gases into the environment. You might even notice their strong acrid smell from within the cabin, especially when idling at a stop or driving at low speeds in the traffic.
Decreased Fuel Consumption
An EGR valve stuck open adds unaccounted for air to the combustion chamber. This creates a lean air-fuel mixture.
This not only makes the engine weaker and even hotter but also reduces how much fuel you are using.
Don’t let the improve mileage fool you. Running lean has more negative impacts on your engine than the few coins you will save at the pump.
Failed Emission Tests
When the EGR valve is clogged or remains closed, it will reduce the amount of exhaust it recirculates and will no longer cool the combustion chambers as it should.
The temperatures will shoot into the range where NOx gases form during the internal combustion cycle.
With more NOx, you will fail your MOT (or any emissions) test. The check engine light sells you out.
Additionally, any emissions sensors hooked up to your tailpipes will pick up the extra NOx. You will fail the test and could even get a fine depending on your local emission laws.
Your Engine Will Start Knocking
By reducing cylinder temperatures, the EGR plays a critical role in reducing pre-ignition that leads to engine knock.
If the valve is stuck closed, you won’t reap its cooling benefits. Your chambers will run too hot and fuel will ignite randomly. The result is a characteristic knocking sound common at low RPMs.
Can You Keep Driving With a Vaulty EGR Valve?
By now, you’ve seen the symptoms of a bad EGR system and you could easily deduce that they are serious.
You wouldn’t want to drive a vehicle that stalls, misfires, idles rough, and smells of exhaust fumes.
Additionally, since your vehicle won’t pass emissions tests, it’s technically unroadworthy. You will be impounded in case you get pulled over for an impromptu emissions test.
Note: Driving with a bad EGR system is bad for your engine and the environment. It can cause further damage to the engine and you won’t be as eco friendly as you can be
How to Clean an EGR Valve
Since carbon accumulation is inevitable, manufacturers recommend cleaning or replacing your EGR valve at least once every 20,000 miles or so.
The recommendation varies from engine to engine. Refer to your manual to find out how often you should have your system serviced.
Cleaning an EGR valve isn’t that hard. Here is a step-by-step guide on how to do it.
- Locate the EGR valve in your vehicle. The location and type of valve will vary depending on your vehicle
- Remover any connectors and electronics attached to the valve
- Unbolt the mounting valve and remove the valve
- Be keen to remove and inspect gaskets. If you note uneven wear or damage, you will have to replace them
- Put on safety glasses and protective gloves before the next step
- Spray some EGR valve cleaner onto the visible carbon deposits
- Use a pipe cleaning brush, a dull scrapper or tooth brush to get rid of all the gunk
- If the carbon is caked on, consider soaking the valve in the cleaner for a while before repeating the clean process
- When you are done, wipe off the surfaces using a clean piece of cloth
Reinstall the valve into the engine taking care to include the gaskets in the right order. Once it is firmly torqued to spec, you can crank the engine for a check.
The engine should run better and your check engine light should disappear in a while. Some vehicles might requeir an OBDII scanner to clear the code and drive around for a while to ensure it doesn’t come back on.
What is an EGR Delete
Technically, an EGR system is a compromise that robs the engine of some performance at the expense of reducing noxious emissions.
As such, aftermarket modifications seeking to improve performance get rid of the valve and trick the powertrain control module into thinking the EGR system didn’t exist in the first place or is working optimally.
Your engine will be more powerful than before and more polluting. To some, this is a compromise they are willing to make.
Are EGR Deletes Legal?
It depends on your location and what you use the vehicle for. EGR deletes are illegal in many locations with some form of emissions control.
Tampering with the exhaust system like removing a catalytic converter, the diesel particulate filter, and the EGR system increases your emissions.
This is a willful crime that will attract a fine. Since it renders your vehicle unroadworthy, it could also be a basis for your insurer holding you in breach of contract should investigators realize you modified your EGR system like so.