6 Symptoms Of A Bad EGR Valve

Written By The Motor Guy

Certified ASE Master Automobile Technician

Last updated March 14, 2023

Exhaust gas recirculation is a process used to reduce vehicle emissions by using exhaust gases to reduce the temperature in the combustion chambers in the engine. Sometimes the EGR valve can fail and this can cause a range of engine performance issues.

The symptoms of a bad EGR valve include reduced engine power, engine misfires, reduced fuel economy, difficulty starting the engine, and spark knocking.

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. The purpose of this is to reduce the nitrogen oxide emissions by recirculating a portion of the exhaust gases back to the combustion chamber.

What Are The Signs of a bad EGR valve?

The most common symptom of a bad EGR valve, is an overall reduction in engine performance, especially when accelerating. 

A broken EGR valve will often fail or get stuck in the open or partially open position. This means that exhaust gases are not allowed back into the engine combustion chambers reducing efficiency when more power is needed.

The EGR valve is usually installed on the intake manifold close enough to the exhaust in order to recirculate the gases when necessary.

The ECU analyses the information from several sensors including the engine coolant temperature sensor, the throttle position sensor, and the mass air flow sensor. It uses the information from these sensors to decide whether or not to activate the EGR.

EGR valve
A typical EGR valve with cooler attached

On modern systems equipped with a digital EGR valve, the ECU also follows the EGR 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.

The EGR is constantly exposed to exhaust gases that create carbon deposits over time. A clogged EGR valve may get stuck, producing several problems depending on its final position (open or closed).

Here are the most common signs of a bad EGR valve in more detail:

Symptom 1. Check Engine Light flashing

Check engine light
A check engine light can point to a bad EGR valve

One of the possible signs the EGR valve has gone bad, is when it causes the check engine light to start flashing. If the ECU detects a problem with the emission control system (and the EGR), it may warn you by turning on the check engine or service engine soon light.

It’s usually safe to keep driving with a broken EGR valve, but you should get it checked out as soon as possible.

Symptom 2. Difficulty during engine start

An engine that keeps cutting out on startup can be one of the symptoms of an EGR valve stuck in the open position.

A failed EGR valve, stuck in the open position can make it difficult to start the engine and to keep it running.

Under normal circumstances, the EGR valve should be closed on engine startup, blocking the flow of gases back into the engine. It should stay like this until the engine warms up and the vehicle starts moving.

white smoke from exhaust

If the EGR valve is not operating properly and allowing exhaust fumes to pass into the combustion chambers, this can cause the engine to cut out, especially when the engine is cold. If on engine startup there is a strong smell of fuel coming from the exhaust, or the engine keeps cutting out, this may be caused by a faulty or partially blocked EGR valve. 

Symptom 3. Possible engine misfires 

Another sign the the EGR valve has gone bad, is engine misfires. A bad EGR valve may cause random engine misfires if it is causing a vacuum leak in the engine.

Sometimes and EGR valve will not respond in a timely manner to the ECU and will stay open longer than it should, or open at the wrong time. This can cause a vacuum leak in the intake manifold that can cause an intermittent engine misfire.

If you run an engine diagnostic, you may see error codes such as P0300, P0100, P0101, P0102 or P0104.

These codes can point to leaks in any part of the air intake system, but removal and inspection of the EGR is a good place to start.

Symptom 4. Rough Engine Idle

One of the most common symptoms of EGR valve failure is a rough engine idle, especially when the engine is cold.

EGR valves often fail in the open position, and this will allow exhaust gases to recirculate back into the engine when it’s not desirable for them to do so.

Symptom 5. Reduced engine performance

One of the effects of a bad EGR valve is a decrease in engine performance, especially under heavy acceleration.

If the EGR valve is not responding to the ECU it can affect the power output of the engine. The EGR valve opens and closes in response to the real time conditions of the engine. If it stuck open this can have an adverse effect on the air to fuel ratio in the combustion chambers, resulting in a reduced power output. 

It can also affect the performance of the turbo (if fitted). If the EGR is causing a vacuum leak, this can reduce the efficiency of the turbo, and can cause premature failure of the turbo if left un-repaired.

Symptom 6. Engine Spark Knock

One of the symptoms of an EGR valve stuck in the closed position is spark knock.

Spark knock is a loud knocking noise that can be heard from the engine bay when the engine is accelerating or is under load.

Spark knock can be caused by problems with the EGR valve. If the EGR valve has become blocked or the valve is not opening when it should, this will stop the exhaust fumes from re-entering the engine when needed.

Spark knock can occur when the combustion chamber gets too hot or there is a build up of excessive pressure that causes the fuel to detonate instead of burning smoothly.

spark knocking causes
Spark knock occurs when fuel detonates rather than burning smoothly

One of the primary roles of the EGR valve is to channel cooler exhaust fumes back into the engine to help lower the temperature in the engine and this can help to prevent spark knock. If the EGR valve is not working properly, then there is an increased chance of spark knock occurring.

Spark knock can lead to head gasket failure, damage to the piston rings, combustion chamber, the connecting rods and the pistons. Simply cleaning the EGR valve can help to prevent spark knock from occurring.

What Next – How To Test For A Bad EGR Valve?

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.

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.

bad EGR valve diagnosis

Remove the EGR valve to check physical condition

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.

  1. 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.
  2. 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.
  3. 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.