GM EGR Valve Test (P0401, P0403, P0404, P0405)

TEST 3: EGR Pintle Position Sensor (Road Test)

In this test step, you're gonna' check that the EGR valve is actually opening and closing.

You'll easily accomplish this by road testing the vehicle with your multimeter connected to the pintle position signal Wire of the EGR valve (which is the wire labeled with the letter C).

You'll need to use 2 long jumper wires to connect the multimeter leads (from inside your vehicle) to the EGR valve:

• The red test lead of the multimeter has to connect to the signal wire on the EGR valve.
• The black multimeter test lead has to connect to a good Ground.

This way, you'll be able to read the multimeter from inside the vehicle, since the multimeter leads are not long enough to reach inside the vehicle.

If you haven't already, re-install the EGR valve back to its place on the intake manifold's plenum.

Now, it's never a good idea to drive while being distracted, so I recommend that you have a helper reading the multimeter as you drive (or vice-versa).

OK, here's what you'll do:

Part 1

1. 1

   Connect the red multimeter test lead to the wire (circuit) labeled with the letter C, with a long wire that can reach from inside the vehicle to the engine compartment.
   
   NOTE: The jumper wire has to be long enough so that whomever is helping you read the multimeter, inside the car, can do it comfortably.

2. 2

   Connect the black multimeter test lead to a good Ground point with another jumper wire.
   
   You can Ground the test lead either inside the passenger compartment or directly on the battery negative (-) post.

3. 3

   Start the vehicle and let it idle.
   
   It's important that the engine be at normal operating temperature (or this test will not work).

4. 4

   Your multimeter should display a voltage reading between 0.6 to 0.9 Volts DC.

Part 2

1. 5

   Start driving when everything is set up and ready and the engine is at normal operating temperature.

2. 6

   Every time you accelerate the vehicle, your assistant should notice the 0.6 to 0.9 voltage DC reading go up.
   
   Depending on how much and how hard you accelerate the car, the voltage may go up to about 4 to 4.5 Volts.
   
   The key here is to see the base voltage go up. There's not a specific number you're looking for, so don't worry if this number doesn't go up all the way to 4.5 Volts.

3. 7

   As soon as you let go off of the accelerator pedal, the reading on the multimeter should drop back to down to the initial voltage reading you observed at idle.

The above test checks two very crucial functions of the EGR valve which are: 1) the EGR valve pintle position sensor and 2) the EGR solenoid. Both of these components make up the EGR valve. OK, here are the test interpretations:

CASE 1: Your multimeter displayed 0.6 to 0.9 Volts DC which increased as you accelerated the vehicle. This is the correct test result and it lets you know that the EGR valve is good and that you have an intermittent problem on your hands.

Intermittent problems are hard to solve, since if they're not present and causing the problem (when you test them), there's nothing that can be done to solve them. The only suggestion is to wait a few more days and retest.

CASE 2: Your multimeter displayed 0.6 to 0.9 Volts DC which DID NOT increase when you accelerated the vehicle. This result indicates one of two things: 1.) That the solenoid inside the EGR valve is bad or 2.) the pintle position sensor is bad. To further test this, go to: TEST 6: Testing The EGR Pintle Solenoid.

TEST 4: EGR Pintle Position Sensor 5 Volt Reference Circuit

So far, your TEST 2 result indicates that the EGR valve registered 0 Volts (or close to) when you tested the wire labeled with the letter C.

This test section will help you find out if this is because the EGR valve's pintle position sensor is not getting 5 Volts or if the EGR valve is bad.

The EGR valve receives 5 Volts DC on the wire labeled with the letter D.

This is what you'll need to do:

1. 1

   Place your multimeter's selector in Volts DC mode.

2. 2

   Disconnect the EGR from it's electrical connector.

3. 3

   Probe the wire labeled with the letter D with the red multimeter test lead.

4. 4

   Connect the black multimeter test lead to the negative (-) battery terminal.

5. 5

   Turn the key ON (but engine OFF)

6. 6

   The multimeter should read between 4.5 and 5 Volts DC.

Let's see what your multimeter test results mean:

CASE 1: Your multimeter displayed 4.5 to 5 Volts DC. This is the correct test result and it lets you know that the EGR valve's pintle position sensor is getting the necessary voltage.

The next step, before condemning the EGR valve as bad, is to make sure that these 5 Volts have a good Ground path. For this test, go to: TEST 5: EGR Pintle Position Sensor Ground Circuit.

CASE 2: Your multimeter DID NOT display 4.5 to 5 Volts DC. This result exonerates the EGR valve itself as bad since without these 5 Volts the EGR valve will not function correctly.

Although it's beyond the scope of this article to troubleshoot why this voltage is missing, you now know where your diagnostic needs to focus on.