Purge solenoid

I have a 1990 Chevy beretta with a 3.1 liter V6. It has a Purge solenoid in the front passenger side of vehicle. I would like to know how it works? I'm assuming that this solenoid valve is normally closed, but I don't know if it is activated at start up or certain vehicles speeds. I know it is ground computer controlled, and feed is from ignition switch. I'm also thinking that this control wire is grounded when ignition switch is KOEO. It could also be a bad driver that is shorted.I would just like to know if vehicle has to be moving or do I have to rev engine to see circuit voltage on the control wire.

In normal conditions, if the solenoid is ground-side switched, you should have 12v on both wires with KOEO. If the solenoid is power-side switched, you should have 0v on both wires with KOEO. Your control wire should not be constantly grounded KOEO. What tells you it is grounded? If the control wire is grounded only in the 'Key On' position then this suggests the control wire itself isn't shorted to ground. You'll have to check the inputs needed to make the computer ground the control wire before condemning the computer, and the inputs could vary between vehicles. The vehicle doesn't necessarily have to be moving though. Revving the engine could trigger it, but there could be other variables.

Well I say the driver is grounded with Key On E Off because I used a test light on control wire and it lights ,but K off E off test light didn't light up.

I'll have to do some research on this tomorrow. Like ImBack218, I usually expect these purge valves to not be energized with the key on, but that may not be the case on this vehicle. It's OBD1, and they did some funky stuff back then. :lol:

Just curious, does the solenoid continue to stay grounded with the engine running?

I would really appreciate it. Yes it does stay grounded with engine running. I should be able to hear a click when I remove the connector while key is on ,but I can't seem to hear a click. I do have a paper with all the pin voltages at the computer, and it says that the control wire should have less than 1 volt with key on and .25 volts with engine running and will vary too. I'm thinking it gradually removes the ground on this control wire or while vehicle is moving. I need to remove this solenoid and activated on a bench or something. I did do an ohm test on solenoid and came to 28ohms, but I don't know if that is good or bad for this solenoid.

The purge solenoid on this vehicle is normally closed, and ground side switched. This being an earlier GM vehicle, no true monitoring of the evaporative emissions was performed (i.e. a normal small leak/gross leak monitor common to all modern vehicles). Instead, this system is more of a passive way to reduce fuel evaporation by way of clearing the canister of fuel vapors. The way this is typically performed on this system is by activating the purge solenoid while driving the vehicle for a predetermined amount of time. Some key requirements are that the engine be at operating temperature, the vehicle has been ran a specific amount of time, the vehicle is above a certain speed, and a minimum throttle angle as indicated by the TPS has been reached. This solenoid should not be energized during cranking as far as I can tell, and at no other times as specified by the above enabling conditions. Are you certain that this solenoid is actually grounded, or is there just substantial voltage drop across it's winding? A unenergized solenoid would have 12v on both sides of its connector. An open/high resistance solenoid would have a voltage drop across it if the resistance were high enough, given the impedance of the meter used. I think a good test to determine if this is actually being grounded or not would be to use a test light to battery positive on the control wire. A lit test light would indeed indicate a grounded solenoid, whether through a short to ground or the driver in the computer itself. As far as the specific enabling conditions for this vehicle, this is all I know. Detailed information on enabling conditions on this old of a vehicle are scarce and a little hard to come by. Hope this helped!

So I got a chance to research this one. The GM service info states that the purge solenoid is only run if:

1.) The ECT is above 176 degrees.
2.) The engine is off idle.
3.) Vehicle speed is 5 MPH or more.

It also confirmed our thinking that the valve is normally closed, ground side switched.

You're positive you were connected to the control wire? With your test light connected to B-? If so, then you may be looking at a failed driver. :huh:

Thank you very much. I will try, and meet those conditions, while testing. I am confused on pin voltage paper I have that says with key on voltage should be less than 1 volt on control wire. That would make the control wire a ground with key on and if it's a normally closed valve then it is being held closed. it also says that with engine running the control wire should have .25 volts and will vary. I would think .25 volts is still a ground . Maybe this pin voltage paper is wrong.

mike126 wrote: Thank you very much. I will try, and meet those conditions, while testing. I am confused on pin voltage paper I have that says with key on voltage should be less than 1 volt on control wire. That would make the control wire a ground with key on and if it's a normally closed valve then it is being held closed. it also says that with engine running the control wire should have .25 volts and will vary. I would think .25 volts is still a ground . Maybe this pin voltage paper is wrong.

Yeah, those voltages are directly contradictory to what the theory & operation says. Why you gotta be confusing, Chevy?

I'll see if I can find a pin voltage chart tomorrow. I'm kinda wondering if the stuff I read is wrong...

I doubt it Tyler, as your information matches mine. I know for a fact it would make zero sense to have this solenoid energized during cranking, unless the engineers wanted their fancy new Berettas to suffer no starts after refueling anyways. :silly:

SniperDan wrote: I doubt it Tyler, as your information matches mine. I know for a fact it would make zero sense to have this solenoid energized during cranking, unless the engineers wanted their fancy new Berettas to suffer no starts after refueling anyways. :silly:

Right? :lol: I guess the driver could be stuck on... But then why does the pin voltage chart suggest the circuit is grounded KOEO?

Now there's so few of these on the road anymore, I'll probably never see one in the shop to check it myself.

There's no telling. I'll look for a flowchart on this system and see what sort of cookyness I come up with.

Thank you, and I appreciate any help. I bench tested the purge solenoid ,but forgot to blow air through it. Anyways I just tested the solenoud electrically. I hear no noticeable click. Only a small tiny arcing when I connect to solenoid pin.

I know basic theory says you need a ground and power source for anything to work. I have the power source and the ground. The ecm will switch to ground on ground control systems, but just curious if some assembly worker or soldering technician decided to try something different. My best guess is the driver in this circuit is shorted to ground. I'm also wondering if this solenoid is bad because I don't hear any clicking when connecting directly to power and ground.

mike126 wrote: The ecm will switch to ground on ground control systems, but just curious if some assembly worker or soldering technician decided to try something different. My best guess is the driver in this circuit is shorted to ground.

I wonder about this, too, but SniperDan mentioned that there should be other symptoms associated with that.

I'm also wondering if this solenoid is bad because I don't hear any clicking when connecting directly to power and ground.

Perhaps? Or, maybe the solenoid shorted and damaged the driver in the process. Do you notice any other driveability problems?


Also, I looked up the pinout chart on Mitchell, and it said exactly the same thing. :ohmy:

Tyler wrote: I'll have to do some research on this tomorrow. Like ImBack218, I usually expect these purge valves to not be energized with the key on, but that may not be the case on this vehicle. It's OBD1, and they did some funky stuff back then. :lol:

Just curious, does the solenoid continue to stay grounded with the engine running?

Tyler and the OP. I believe on this early system the purge valve and flow rate is controlled primarily by a ported vacuum source. It may be a default to have the purge valve open with the key on and during start up because there is no ported vacuum until you open the throttle.
I'm not sure if it is PWM after that, but I can see no other reason to make it computer controlled if it wasn't. It's not like they shut it off to do EVAP monitoring as this is too old.

ScannerDanner wrote: Tyler and the OP. I believe on this early system the purge valve and flow rate is controlled primarily by a ported vacuum source. It may be a default to have the purge valve open with the key on and during start up because there is no ported vacuum until you open the throttle.
I'm not sure if it is PWM after that, but I can see no other reason to make it computer controlled if it wasn't. It's not like they shut it off to do EVAP monitoring as this is too old.

This makes way more sense! mike126, can you trace out where the purge line ends up, exactly?