The Exhaust Gas Recirculation Valve (also known as EGR) is a key component of the secondary emissions control system. The symptoms of a bad EGR valve will leave your engine running badly or maybe not at all.
The job of the exhaust recirculation valve (EGR valve) is to reduce the nitrogen oxide (NOx) emissions by means of recirculating a portion of the exhaust gases back to the combustion chamber.
Over time, the EGR valve can become dirty and blocked with carbon deposits from the exhaust gases. This can eventually lead to the failure of the EGR valve and it's not something you will be able to ignore for too long.
What Is An EGR Valve
The EGR valve works by re-routing exhaust gases back into the engine at certain times, usually when the engine is not under excess load.
So does recirculating exhaust gases not harm the combustion process? The short answer is yes and no. Overall efficiency will drop but the inert gases will not alter the air/fuel ratio because the Electronic Control Unit (ECU) is aware of EGR operation and will adapt fuel delivery accordingly.
The rationale supporting the use of an EGR valve is the NOx emissions reduction. Nitrogen oxide gases are very dangerous, the objective of recirculating a small portion of exhaust gases is reducing the combustion temperature under certain conditions and hence drop Nox emissions to a minimum.
How Does An EGR Valve Work?
The EGR valve is usually installed on the intake manifold close enough to the exhaust in order to recirculate the gases when necessary. The Electronic Control Unit (ECU) analyses the information from several sensors including the engine coolant temperature sensor (ECT), the throttle position sensor (TPS), and the mass air flow sensor (MAF). It uses the information from these sensors to decide whether or not to activate the EGR.
On modern systems equipped with a digital EGR valve, the ECU also follows, in real time, the valve aperture using an integrated EGR pintle position sensor.
Internally the construction of the exhaust recirculation valve is very simple. Some models use a flap design (similar to the throttle body), others use a linear valve design. But make no mistake, this simple design is necessary to help the valve withstand its aggressive operating conditions. The EGR is constantly exposed to the exhaust gases which tend to create carbon deposits over time. A clogged EGR valve may get stuck, producing several problems depending on its final position (open or closed). That’s why is important to perform routine maintenance to the valve to keep it in good condition.
6 Symptoms Of A Failing EGR Valve
The most common symptoms of a bad exhaust gas recirculation valve are:
- Check Engine Light (CEL) on: due to its crucial role in emissions control expect the Check engine light to come on after driving for a while with a damaged EGR valve.
- Difficulty during engine start: an EGR valve stuck in the open position can make it difficult to start the engine.
- Possible engine misfires: a deteriorated or clogged EGR valve may cause misfires depending on the driving condition.
- Rough Engine Idle: depending on the vehicle year and maker the ECU may not compensate for this failure during idle. This might cause a rough idle.
- Reduced engine performance: a deficient exhaust recirculating valve may cause performance issue under any driving condition.
- Engine Spark Knock: when the EGR valve is not working properly the recirculation of gases is uncontrolled. The combustion is vastly affected producing spark knocks. An extreme spark knock could damage the compression ring or the piston head itself.
How Do You Diagnose A Failing EGR Valve?
For the purpose of this article, it’s assumed that you have a basic knowledge of safety precautions while working on your vehicle.
You may need one or more of the following tools:
- OBD2 Code Reader
- Digital Volt-Ohm meter
- Professional Automotive Scan Tool.
- Vacuum gauge with proper adapters.
- Manual vacuum pump with proper adapters.
Always refer to the appropriate OEM literature when possible. Original manufacturer diagnostic procedures should always have precedence over a generic workflow.
1. Preliminary steps
Recommended tools: OBD2 Code Reader / automotive scan tool
> Data trouble codes: using an OBD2 code reader take note of any DTC present in the ECU memory. For doing so you only need to connect your code reader and turn the ignition key on (engine off), a state usually known as KOEO.
> Data trouble codes clear: now that you know what codes were stored into memory you need to clear them. This is usually done selecting “clear codes” in your tool.
2. Visual Inspection
Recommended tools: none
> Vacuum line: on vacuum controlled EGR valves, disconnect the vacuum line and perform a visual inspection of its condition. Look for signs of worn or deterioration. Pay special attention to possible holes in the vacuum line. Ideally, a vacuum line test using a manual vacuum pump should be performed. You could also use the manual vacuum pump to operate the EGR and check that it's working properly.
> Exhaust Gas Recirculation valve inspection: perform a thorough inspection of the EGR valve exterior, tubing, and connections. Look for possible exhaust leaks in the EGR gasket and connections. Replace the gasket and/or EGR valve if necessary.
Fix any wiring problem before continuing.
3. Electrical Tests
Recommended tools: digital volt-ohm meter (DVOM)
IMPORTANT: there are many different EGR implementations on the market. The following tests only apply to digital EGR models. It’s highly recommended to find a reliable information source containing the proper wiring diagrams before doing any electrical test.
> Reference voltage: as mentioned earlier in the article, some modern designs include a pintle position sensor. Internally, that sensor is nothing more than a linear potentiometer. Refer to the appropriate wiring diagram to identify your connector signals. In order to measure the reference voltage, you will need to enter in KOEO mode (Key On Engine Off) and turn the digital multimeter dial to “voltage” test mode. Unplug the EGR connector. Now place one multimeter lead in a known ground (battery negative is a good one) and the other probe tip in the terminal of the EGR wiring harness corresponding to the ECU reference. If there is no voltage (or is below 4V) then you must check the continuity and electrical resistance of the wire from the terminal all the way to the ECU itself.
> Ground test: this test assumes that you found a good reference voltage coming from the ECU. Once again, enter in KOEO mode (Key On Engine Off) turn the digital multimeter dial to “voltage” test mode and place one probe tip on the EGR harness terminal corresponding to the reference voltage and the other on the terminal that should be the ground. Ideally, the voltage would be the same value as the previous test, if the difference is greater than 10% then you will need to check electrical resistance and continuity of the ground line from the EGR harness all the way down to the ECU.
> Solenoid voltages: electronically controlled EGR valves could use one or more solenoids to control de valve aperture movements (open/close). Refer to the appropriate wiring diagram and locate EGR solenoid supply voltage, and/or solenoid control signals (usually EGR SOL HIGH/LOW). Using the digital volt-ohm meter check each voltage.
> Solenoid functional test: using extreme caution and the proper wiring diagram operate the EGR valve solenoid applying the 12V supply voltage to the corresponding terminal. Perform this test directly on the EGR (electrical connector disconnected) to avoid accidental ECU damage.> Solenoid functional test:
4. Scan Tool Tests
Recommended tools: automotive scan tool with live data capabilities.
> Exhaust Gas Recirculation Valve live test: depending on the vehicle year and model, using an automotive diagnostic scanner you can perform a EGR “live test”. First, enter in KOEO mode and lock the EGR related data on the display. Depending on your vehicle and scan tool maker you may have several items to check. Focus on the EGR position voltage output, EGR aperture (often expressed as %), EGR solenoid activation, and RPM. Once you are ready, start the engine to enter KOER mode. Accelerate and deaccelerate the engine. Watch the EGR data carefully. The aperture should change depending on RPM, usually, the valve is closed at idle and opens while accelerating.
> Exhaust Gas Recirculation Valve functional test: depending on the vehicle year, model and scan tool you may be able to perform a functional test of the EGR valve. Refer to the scan tool manual for detailed instructions. Basically, the functional test allows you to open/close the EGR valve and verify is working properly.
How To Clean A Clogged or Dirty EGR Valve
IMPORTANT: always read the EGR cleaner instructions before proceeding.
Due to its working conditions, it’s not uncommon to find the EGR valve clogged with carbon deposits. It can be difficult to prevent the build up, especially when engines get older and have higher mileage.
There are a couple of different solutions to the problem, depending on the severity of the blockage.
- Clean using a professional EGR cleaner spray: this method has the advantage of being straightforward and time-effective because you don’t need to remove the valve from the engine.
- Using a carburetor cleaner spray: this alternative requires removing the EGR from the engine and then clean it with a metal toothbrush and carburetor cleaner. This method consumes a lot of time, not to mention the exposure to an aggressive product as the carburetor cleaner. However, it’s a better option than replacing the valve.
- Replacing the EGR Valve: this is the most radical solution, but inevitably at some point, you will need to replace the valve.
This article will assume you will choose the easier alternative: using a professional EGR valve cleaner.
> Preliminary steps: warm-up the engine until it reaches its normal operating temperature.
> Remove air filter or air intake hose: depending on your engine you will need to choose a method to access the air intake system. You will need to spray the product on the air intake. Usually, its easier to remove the air hose, but be aware that you can’t bypass the MAF sensor or vehicle will be unable to work properly.
> Spray the EGR cleaner into the air stream: increase the engine revolutions to approximately 2000 RPM (consult your product for exact instructions). Then spray the product in short bursts, usually one second each. The RPM will drop momentarily. That’s normal, wait a few seconds allowing the engine to burn the cleaner. Repeat the procedure until the bottle is empty. Maintain the 2000 RPM at all times, increase them if necessary to avoid stalling. Keep the engine running during 3-5 minutes before shutting it off. Ideally, you should perform a test drive, don’t exceed 3000 RPM though.
If the spray cleaner doesn’t improve the EGR performance you may need to service the valve. As explained above that implies removing the EGR from the engine and clean it using a carburetor cleaner. A highly clogged valve will not be recovered even using this kind of products. If that’s the case you will need to replace it.