2000 Chevy Astro testing EGR valve power (12v) circuit

[Solo57]

Hi, I have a P0300 code on my 2000 Chevy Astro, I have checked several variables and now I happen to be trouble shooting the EGR valve and every thing have tested ok on all A B C D connector' s wires except power (12 V) circuit wire (E). when I probed wire E being disconnected from the EGR with my DVOM set on DC mode, key on but without cranking engine, the meter read 11.83 Volts but when I probed it connected to the EGR valve the meter read 85.9 mV.
Does anyone know if this is normal or the test results mean i have short on wire E or is it possible the valve it's self is shorted to ground within it' s circuit?

[Blue Bowtie]

Welcome Aboard!

That can be normal since the power for the EGR on the red E wire is sourced from the PCM, connector C4 / pin 16. That source is through one of the PCMs quad drivers, essentially a transistor output to the EGR. Voltage will leak through the output transistor even when the transistor is off, but this leakage voltage is pulled down when the load (EGR valve) is connected.

If you have a bi-directional scanner available, you can force the EGR on to 100% duty cycle and read the voltage at the E terminal, which should then be in the range of 12-14V.

[Blue Bowtie]

Incidentally, while a leaking EGR can contribute to a rought idle and misfire in the lower RPM ranges, it is very common to generate that P0300 (Multiple/Random Misfire) due to an ingtition coil secondary problem, such as breakdown of the distributor cap and rotor, or failing ignition coil.

[brcidd]

I had several Astro vans in 90's. The most common issue with that code was the valve would not seat right- stick open- but it has nothing to do with the control system-or the wiring or the connectors- and everything to do with the sh*t build-up on the pintle valve. It got so I used to just pull them out to clean them when I saw that dreaded code. A stealership would replace the entire valve- yes, the new one is clean--but I found that just cleaning the old one with a wire brush and carb cleaner would rid the code and it's a whole lot cheaper. Be wary that the two bolts that hold it in place extend inside the manifold and you will get about a half turn out after you break it loose and it will start to turn extremely hard due to the crud in the threads behind the manifold. I twisted my first on off- and ran it with only one bolt for several years. From then on- care to "work it" in and out made it so the bolt does not twist off. The only other choice is to remove the manifold- yeah- right....

You are assuming the code means control issues--don't forget about crud build-up on your pintle valve.

I can remember being stalled at a gas station with stock trailer in tow- and having that code along with a no start condition- and having the wife pull me home 8 miles with an S-15 pick-up!!! (back roads and no AAA back then). I found out that you can start it with a stuck open EGR if you mash the gas pedal to the floor while cranking- but it runs really rough- but it will get you home so you can clean it out the next day.

[Solo57]

Thank you Blue Bowtie, This makes sense I will try to get one bi-directional scanner but before I do that I like to make you aware that I did the same tests with a test light, it turns out that the red E power wire lights up when back probed with test light connected to battery positive, could you please confirm if this is normal as well? (When I back probe it test lamp connected to negative battery, it does not light up as it then should)
Using the test lamp I also back probed wire disconnected from the EGR valve and connected to battery negative. Test lamp lights up extremely dimmed .
FYI my van does runs but it runs very rough at idle and does not go more than 30 MPH on the road, The scanner shows it is lean 25% and up both banks but it levels to normal over 1900-2000 RPM

see pictures attached

[Solo57]

Originally Posted by brcidd

I had several Astro vans in 90's. The most common issue with that code was the valve would not seat right- stick open- but it has nothing to do with the control system-or the wiring or the connectors- and everything to do with the sh*t build-up on the pintle valve. It got so I used to just pull them out to clean them when I saw that dreaded code. A stealership would replace the entire valve- yes, the new one is clean--but I found that just cleaning the old one with a wire brush and carb cleaner would rid the code and it's a whole lot cheaper. Be wary that the two bolts that hold it in place extend inside the manifold and you will get about a half turn out after you break it loose and it will start to turn extremely hard due to the crud in the threads behind the manifold. I twisted my first on off- and ran it with only one bolt for several years. From then on- care to "work it" in and out made it so the bolt does not twist off. The only other choice is to remove the manifold- yeah- right....

You are assuming the code means control issues--don't forget about crud build-up on your pintle valve.

I can remember being stalled at a gas station with stock trailer in tow- and having that code along with a no start condition- and having the wife pull me home 8 miles with an S-15 pick-up!!! (back roads and no AAA back then). I found out that you can start it with a stuck open EGR if you mash the gas pedal to the floor while cranking- but it runs really rough- but it will get you home so you can clean it out the next day.

Thank you Brcidd,
I tested the EGR Valve's pintle on the bench and it works fine and there is no blockage in it or inside the manifold.

That was quite a tow!

Best regards.