TEST 7: Clogged Intake Manifold

If you're coming from TEST 5, so far you have verified two very important things:

  1. In TEST 1, you verified that the EGR valve is producing the correct voltage signal with the Key On Engine Off.
  2. In TEST 5, you verified that the EGR valve pintle is producing the correct voltage across the entire pintle's movement.

If you're coming from TEST 6, so far you have verified two very important things:

  1. In TEST 1, you verified that the EGR valve is producing a high voltage signal with the Key On Engine Off.
  2. In TEST 6, you verified that the EGR valve orifices, in the intake plenum, were not clogged.

The next step is to see if the EGR passage (which is not visible to the eye) inside the intake manifold's plenum is clogged. This takes a very particular test.

What you'll need to do now is to start the engine with the EGR valve off of the intake plenum. This is what you need to do:

  1. 1

    With the EGR valve removed from the intake manifold, have a helper start the engine.

  2. 2

    You'll notice one of two things:

    The engine will start and run smoothly (as if the EGR valve where still there in its place).

    Or the engine will start and idle extremely high and/or stall immediately.

  3. 3

    If the engine starts and idles very very high have your helper immediately turn off the engine.

Let's take a look at your test results:

CASE 1: If the engine started and idled smooth. Then this confirms beyond a shadow of a doubt that the EGR passages are clogged inside the intake's plenum.

This also confirms that this is the reason for diagnostic trouble code P0401.

You'll need to remove the intake manifold's plenum to physically remove this carbon blockage. I have used a piece of coat hanger wire as a snake (along with a lot of Carburetor Cleaner Spray) to remove this blockage and you'll need to do the same.

CASE 2: If the engine started and idled very high and/or stalled. Then this confirms that the EGR passages inside the plenum ARE NOT clogged.

Your next step is to check that the EGR pintle's motor is getting power. Go to TEST 2: Testing The Power (12 V) Circuit (if the pintle's motor does not get power... when the PCM commands the EGR valve to open, the EGR won't be able to).

If after checking and confirming that the EGR Solenoid (inside the EGR valve) is OK, then check out the suggestion in TEST 9.

TEST 8: EGR Solenoid Resistance

Testing The EGR Solenoid Resistance. How To Test The GM EGR Valve Buick, Chevy, Olds, Pontiac Testing The EGR Solenoid Resistance. How To Test The GM EGR Valve Buick, Chevy, Olds, Pontiac

OK, in TEST 2 you verified that the EGR solenoid is getting power (10 to 12 Volts DC). The next step is to measure the resistance of the solenoid itself.

What sucks about this test is not that it's hard to do, but that the EGR valve has to be at room temperature. Why? Well the specs I'm providing for you are with the EGR valve at room temperature... so keep this in mind when doing this test.

Let's get started:

  1. 1

    Place your multimeter in Ohms mode (Ω).

  2. 2

    Disconnect the EGR's electrical connector.

  3. 3

    With the multimeter leads, measure the resistance across the EGR valve pins that connect to wires labeled with the letter A and the letter E.

  4. 4

    If the EGR Solenoid is OK, your multimeter should read 8 to 9 Ohms.

Let's take a look at your test result:

CASE 1: The multimeter registered the indicated Ohms. This result tells you that the EGR solenoid is OK.

So far, you have verified two important things, 1.) The EGR solenoid is getting power and 2.) the solenoid itself passed the resistance test. This leaves two possibilities for the P0403 DTC and they are:

  1. A problem in the wire labeled with letter A (between the EGR connector and the PCM connector).
  2. Or the PCM is BAD (although this is very rare).

Testing the two above conditions are beyond the scope of this article, but now at least you know what your next steps are.

CASE 2: The multimeter DID NOT register the indicated Ohms. This result tells you that the EGR solenoid is fried. Replacing the EGR valve will solve the EGR DTC P0403.