How To Test The EGR Valve (1994-1995 2.2L Chevrolet S10, GMC Sonoma)

Testing the EGR valve on your 2.2L Chevrolet S10 or GMC Sonoma isn't difficult, and what's more, you don't need any expensive diagnostic equipment.

In this tutorial, I'll explain how to determine if it's good or bad step by step.

You can find this tutorial in Spanish here: Cómo Probar La Válvula EGR (1994-1995 2.2L Chevrolet S10, GMC Sonoma) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 2.2L Chevrolet S10: 1994, 1995.
• 2.2L GMC Sonoma: 1994, 1995.

Symptoms Of A Bad EGR Valve

The EGR valve is the component tasked with allowing a metered amount of exhaust gas into the intake manifold.

The exhaust gas entering the intake manifold helps reduce the amount of oxides of nitrogen the engine produces during the combustion process.

The exhaust gas recirculation should only occur when 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 should be closed, thus 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 one of the following OBD I trouble codes:

• Code 32: EGR system problem.
• Code 33: MAP sensor signal High.

You're also going to see one or more of the following symptoms:

• Rough idle.
• Bad gas mileage.

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

The tool that is going to make testing the EGR valve a breeze is a handheld vacuum pump.

If you don't have one, 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 one, this is my recommendation: Actron CP7835 Vacuum Pump.

TEST 1: Checking For Continuous Vacuum To EGR Valve

As mentioned earlier, the fuel injection computer controls the EGR valve by commanding the EGR valve solenoid to allow/cut off vacuum to the EGR valve.

When the EGR valve receives vacuum, it opens. When the supply of vacuum is cut-off, the EGR valve closes.

When the engine is idling, the EGR valve should not receive any vacuum from the EGR valve solenoid.

For our first test, we'll check that the EGR valve IS NOT receiving vacuum while the engine is idling.

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

Let's get going:

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 solenoid is defective.
• The vacuum hose is attached to the wrong port on the EGR 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.

• How To Test The EGR Vacuum Solenoid (1994-1995 Chevrolet S10, GMC Sonoma).