How To Test The EGR Valve (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma)

In this tutorial, you'll find a step-by-step guide to troubleshooting the EGR valve as good or bad.

All four EGR valve test steps are explained in detail so you can quickly and easily troubleshoot the EGR valve as good or bad.

APPLIES TO: This tutorial applies to the following vehicles:

• 2.8L Chevrolet S10 Pickup: 1988, 1989, 1990, 1991, 1992, 1993.
• 2.8L GMC S15 Pickup: 1988, 1989, 1990.
• 2.8L GMC Sonoma: 1991, 1992, 1993.

NOTE: You can find the EVRV solenoid test here:

• How To Test The EVRV Solenoid (1988-1993 2.8L Chevrolet S10, GMC S15 Pickup, GMC Sonoma).

Symptoms Of A Bad EGR Valve

The purpose of the EGR valve is to control the amount of nitrogen oxides (NOx) that the engine produces under load.

This is achieved when the EGR valve receives vacuum from the EGR vacuum solenoid, causing the EGR valve diaphragm to open.

When the diaphragm of the EGR valve opens, the stem (pintle) of the valve also opens as the two are connected.

Once the EGR valve pintle opens, the valve allows a metered amount of exhaust gas to flow into the intake manifold.

The EGR valve only allows exhaust gas recirculation if the following three conditions are met:

• The engine has reached normal operating temperature.
• The engine is under load.
• The fuel injection computer commands the EGR solenoid to supply vacuum to the EGR valve.

When the engine is idling, the EGR valve is closed, preventing any exhaust gas from entering the intake manifold.

Depending on the nature of the EGR system failure you may or may not notice any engine performance issues when the fuel injection computer lights up the check engine light with an EGR system diagnostic trouble code.

When an EGR valve system failure occurs, the fuel injection computer usually sets an EGR valve diagnostic trouble code. If it does, you'll see the following OBD I trouble code:

• Code 32: EGR System Problem.

You'll also see one or more of the following symptoms:

• Rough idle.
• Bad gas mileage.
• Engine knock (pinging).
• Engine hesitation when accelerating the vehicle.

Important Testing Tips

TIP 1: The EGR valve can get very hot (when the engine is running). Start the EGR valve test with a cold engine.

TIP 2: You may need to remove the EGR valve to test it. You can reuse the same EGR valve gasket if it isn't damaged.

Whether you reuse the same gasket or install a new one, you must install the gasket dry. In other words: DO NOT use any sealer (like RTV Silicone) on it.

What Tools Do I Need To Test The EGR Valve

I'm going to recommend two tools that will make your life easy when testing the EGR valve.

• A handheld vacuum pump.
• A telescoping mirror.

If you don't have a vacuum pump, you can borrow one from your local auto parts store (for a small deposit that they'll return to you once you return the tool -AutoZone, O'Reilly Auto Parts).

If you'd like to buy a vacuum pump, this is my recommendation: Actron CP7835 Vacuum Pump (at: amazon.com).

TEST 1: Checking For Continuous Vacuum To EGR Valve

For our first test, we'll check that the EGR valve isn't receiving continuous vacuum when the engine is running in idle RPM.

If vacuum is not present in the EGR valve's vacuum line, we'll move on to TEST 2.

IMPORTANT: Be careful and take all necessary safety precautions while working around a running engine.

OK, these are the test steps:

1. 1

   Disconnect the vacuum hose that connects to the EGR valve vacuum port.
   
   Leave the other end that connects to the EGR vacuum solenoid connected to it.

2. 2

   Connect a vacuum gauge to the vacuum hose you just disconnected from the EGR valve.
   
   NOTE: If you don't have a vacuum gauge, don't panic. You can still check to see if vacuum is present in the vacuum hose.

3. 3

   Start the engine and let it idle.

4. 4

   The vacuum hose you just disconnected should not have vacuum.

Let's take a look at what your test results mean:

CASE 1: Vacuum WAS NOT present. This is the correct and expected test result since manifold vacuum should NOT be present when the engine is idling.

The next step is to apply vacuum to the EGR valve while the engine is idling. For this test, go to: TEST 2: Applying Vacuum To The EGR Valve.

CASE 2: Vacuum was present. This is a problem since vacuum should not be present when the engine is idling.

Vacuum present in the vacuum hose is usually caused by one of the following issues:

• The EGR vacuum solenoid is defective (this solenoid is known as the EVRV solenoid).
• The vacuum hose is attached to the wrong port on the EGR vacuum solenoid.

Your next step is to check that the vacuum hose connected to the EGR valve is routed correctly. If the vacuum hose is going to the right place (the EGR vacuum solenoid), your next step is to test the EGR vacuum solenoid (known as the EVRV solenoid).

• How To Test The EVRV Solenoid (1988-1995 2.8L TBI Chevrolet S10, GMC Sonoma)