DIY

Bad EGR Valve: Common Symptoms and Testing Procedure

Reading Time: 4 minutes

Nitrogen oxides (NOx) from a car’s tailpipe can contribute to the formation of photochemical smog pollution. All modern gas-powered vehicles (and most diesel applications) combat the problem by limiting NOx emissions with an exhaust gas recirculation (EGR) system. The EGR valve is the heart of the EGR system.

Like any other auto part, the EGR valve can eventually fail. When that happens, you’ll likely notice your vehicle exhibiting one or more undesirable symptoms.

What is an EGR Valve?

As was mentioned, the EGR system reduces the amount of NOx emissions leaving the vehicle’s tailpipe. The system does this by recirculating spent exhaust gases back into the engine to lower combustion temperatures. By replacing a portion of the engine’s normal air-fuel mixture with inert exhaust gas, the temperature of combustion is reduced, which also limits the formation of NOx.

egr valve of a car
All modern gas-powered vehicles (and most diesel applications) limit NOx emissions with an EGR system.

But exhaust gases can only be introduced into the engine under certain conditions. If EGR takes place at the wrong time, the vehicle will suffer from engine performance problems. For this reason, the EGR system contains an EGR valve to regulate the flow of exhaust gases.

Typically, the EGR valve’s location is on the engine’s intake manifold. A tube connects the valve to the exhaust manifold. When the conditions are correct, the EGR valve opens, allowing exhaust gases to enter the engine, where they are burned as part of the normal combustion process.

There are many different EGR system designs in use today. In some older vehicles, the EGR valve is operated directly by engine vacuum and exhaust backpressure. Most modern vehicles, however, use one or more electronically-controlled solenoids. The solenoids may control the vacuum supply to the EGR valve or operate the valve directly.

A computer, which is often referred to as the powertrain control module (PCM), operates the solenoids based on input from various sensors.

Symptoms of a Bad EGR Valve

When the EGR valve fails, it can cause several noticeable symptoms. Here are the most common:

Illuminated Check Engine Light

The PCM monitors the performance of the EGR system. If the module detects a problem, it will turn on the check engine light and store a corresponding diagnostic trouble code (DTC) in its memory.

Engine Performance Problems

When the EGR valve is on the fritz, it can cause various engine performance problems, including a rough idle, stalling, surging, and hesitation.

Spark Knock (Detonation)

An EGR valve that’s stuck closed can lead to abnormally high combustion temperatures, resulting in spark knock (also known as detonation). If left unchecked, that spark knock can cause costly engine damage.

Hard Starting

Although somewhat rare, if the EGR valve is stuck wide open, it can make the vehicle difficult to start.

Increased Tailpipe Emissions

When the EGR valve fails, it can cause an increase in Nitrogen oxides (NOx), hydrocarbons (HC), or both. If you live in a location that requires emissions testing, an increase in these pollutants will cause your car to fail the test.

replacing egr valve
Cars built after 1996 with OBD II will usually set a code when there’s an issue with the EGR system, as will some older cars with OBD I.

How to Test The EGR Valve

Several different problems can mimic a bad EGR valve. To ensure the valve is to blame, you’ll want to perform a thorough diagnosis of the vehicle by doing the following:

Step 1. Check for Diagnostic Trouble Codes (DTCs)

The first thing you’ll want to do is check for DTCs that could narrow down the troubleshooting process. Cars built after 1996 with onboard diagnostics (OBD) II will usually set a code when there’s an issue with the EGR system, as will some older cars with OBD I.

You can check for diagnostic trouble codes using a scan tool or code reader. These days, you can even get an inexpensive OBD II code reader for your smartphone.

It’s important to point out that DTCs do not tell you the exact problem with the car. Codes merely serve as a starting point for further diagnostics.

Step 2. Perform a Visual Inspection

Next, you’ll want to perform a visual inspection. Look for issues, such as broken wires and damaged vacuum hoses in the EGR valve’s control system.

Repair any issues found during the visual inspection, clear the DTCs, and see whether the problem returns.

Step 3. Test the EGR Valve

Because there are so many different EGR system designs in use today, there isn’t a one-size-fits-all test method for the EGR valve. To properly troubleshoot the EGR system on your vehicle, you’ll want to consult the appropriate information in a repair manual or repair database.

replacement egr valve
Expect to pay somewhere between $350 and $1,000 to have a professional replace the EGR valve for you.

How Much Does an EGR Valve Cost?

Expect to pay somewhere between $350 and $1000 to have a professional replace the EGR valve for you. If you do the job yourself, expect to pay anywhere between $20 and $800 for the part. The exact price of the repair will depend on several factors, such as the year, make, and model of your vehicle.

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