TEST 1: First Things First

The most common problem on this type of GM EGR valve setup is carbon blocking the EGR pintle from fully extending and preventing exhaust gas flow into the intake manifold or blockage inside the intake manifold's plenum.

The EGR valve does go bad, but not very often. So the very first thing you need to do is to see if the EGR code that's lighting up the check engine light (CEL) or the rough idle your car is experiencing is due to a bad EGR pintle position sensor.

If you got EGR valve DTC P0403, you can skip this test and start with TEST 2.

We need a good and logical starting point for our tests, so first you'll check the EGR pintle position with a multimeter and depending on the result of this test, you'll know where to go from there.

NOTE: The EGR valve needs to remain connected to its electrical connector to perform this test. You'll need to back probe the connector or use a wire piercing probe on the wire. You can see an example of this tool here: Wire-Piercing Probe.

Let's get started:

  1. 1

    Place your multimeter in Volts DC.

  2. 2

    With the red multimeter test lead and an appropriate tool, probe the circuit labeled with the letter C.

  3. 3

    Connect the black lead of the multimeter to a good Ground point on the engine or battery negative terminal.

  4. 4

    Turn the Key on but don't crank or start the engine.

  5. 5

    Your multimeter should display a voltage reading between 0.6 to 0.9 Volts DC if all is OK.

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

CASE 1: If your multimeter displayed 0.6 to 0.9 Volts DC. So far so good since this is the correct and expected test result. Your next step is to go to: TEST 5: Verifying The EGR Signal.

The next step (TEST 5) is to remove the EGR from the intake manifold and manually induce the EGR valve to produce the entire range of the pintle position voltage values (by pushing the EGR's pintle in and out with a small screw-driver) to make sure the pintle position sensor inside the EGR valve is good.

CASE 2: If your multimeter displayed a DC voltage above 0.9 Volts. This is an indication that a piece or pieces of carbon are blocking the EGR valve's pintle from fully seating. Go to: TEST 6: Checking for Carbon Blockage.

CASE 3: If your multimeter DID NOT display any voltage or a very low voltage. Re-check all of your connections and redo the test.

If still no voltage or a voltage way lower than the 0.9 Volts specified, then this confirms the EGR P0405 (EGR Pintle Position Low Voltage) diagnostic trouble code.

This low or non-existent voltage output is usually due to the 5 Volt Reference Voltage (that powers the pintle position sensor inside the EGR valve) is missing. So, to check for this, go to: TEST 3: 5 Volt Reference Circuit.

TEST 2: Testing The Power (12 V) Circuit

The EGR valve has a solenoid, that when commanded On by the PCM, it opens the EGR's pintle to let exhaust gas circulate back into the engine.

If the EGR solenoid does not get power (10 to 12 Volts) or the solenoid is bad, the PCM will set a P0403 DTC. So, this test will check to see if this part of the EGR valve is getting power.

This a very simple test for which you can use a multimeter or a test light to accomplish. You can test for power with the EGR valve connected or disconnected to its connector. Of course, what I recommend you do is to test it connected to its connector and with a wire piercing probe piercing the wire to get at the voltage.

If you decide to probe the front of the female terminal, be careful not to damage it.

OK here's the test:

  1. 1

    Place your multimeter in Volts DC mode.

    Don't have a digital multimeter? Need to buy one? Check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.

  2. 2

    Probe the wire (with an appropriate tool) labeled with the letter E with red multimeter test lead (see photos in image viewer).

  3. 3

    Connect the black multimeter test lead to a good Ground point on the engine or to the battery negative terminal.

  4. 4

    Turn the Key on but don't crank or start the engine.

  5. 5

    The multimeter should read 10 to 12 Volts.

Let's examine your test result:

CASE 1: If the multimeter registered 10 to 12 Volts. This test result tells you that the power circuit is OK.

The next step is to check the EGR solenoid's resistance (with your multimeter) to see if it's fried. So, for this test go to: TEST 8: EGR Solenoid Resistance.

CASE 2: If the multimeter DID not register 10 to 12 Volts. This test result tells you that there's something wrong with the circuit. Without these 10 to 12 Volts, the EGR valve will not function. Repair the fault in this circuit before continuing.