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I'll working on a 3.5 impala that has a evap vent valve circuit code (can't remember which one off hand now) and here's where I'm at.
Bench tested the valve, got a slight click but no valve movement. Harness has 12v both when I bi-directionally open and close the valve. No change in voltage. Load pro indicates massive voltage drop in the circuit.
Am I looking for a short to ground here or could it be a computer issue that is applying a constant ground. The voltage drop is what has me thinking a short though.
fueltank pressure sensor voltage should be 1.5 volts with the capoff. ive seen a bad pressure sensor cause a vent code. but if i were you id put my test light in place of the valve and look for it to turn on and off with a scanner
cheryl hartkorn wrote: fueltank pressure sensor voltage should be 1.5 volts with the capoff. ive seen a bad pressure sensor cause a vent code. but if i were you id put my test light in place of the valve and look for it to turn on and off with a scanner
Thanks Cheryl. I'm having a hard time understanding why there is always 12v at that connector if it's supposed to be a ground side switch? Wouldn't there only be 12v when I turn the valve on with my scan tool unless there is a bad wire being ground somewhere else?
When you command the valve on, do you have 12V on both wires? Or just one? On a working system, with the valve commanded on, you'd have 12V on one wire and 0V on the other.
Which wire was shown to have a massive voltage drop by the LoadPro?
Tyler wrote: When you command the valve on, do you have 12V on both wires? Or just one? On a working system, with the valve commanded on, you'd have 12V on one wire and 0V on the other.
Which wire was shown to have a massive voltage drop by the LoadPro?
Because of voltage drop, right? I cant remember now if they both had power, I just thought it was off that there was power with it on and off. The loadpro showed drop on the power wire.
with the connector plugged into the valve you should have 12V if you back probe both wires. with the valve commanded on you should have 12v on the red/white wire and 0v on the white wire.
So the ecm is grounding that solenoid with the white wire. check for ground at the ecm when you are commanding the valve on. with and without the solenoid plugged in
Nandor69 wrote: with the connector plugged into the valve you should have 12V if you back probe both wires. with the valve commanded on you should have 12v on the red/white wire and 0v on the white wire.
So the ecm is grounding that solenoid with the white wire. check for ground at the ecm when you are commanding the valve on. with and without the solenoid plugged in
I took out the solonoid and replaced it with the volt meter probes. Also used volt meter with + probe on control wire and grounded the other. Got 12v with valve commanded on and off.
Monde wrote: The solenoid should be fine since you have 12v on the control wire.Your next check is for open on the ground (control) wire at the pcm. If you measure 12v there, the wire is fine, and your issue might be with the driver.
Monde wrote: The solenoid should be fine since you have 12v on the control wire.Your next check is for open on the ground (control) wire at the pcm. If you measure 12v there, the wire is fine, and your issue might be with the driver.
Exactly!
Sorry, I feel pretty dense here. Doesn't the v meter replacing the solonoid showing 12v show that there is power and ground, a complete circuit? The solonoid is definitely bad. What I'm seeing is 12v with the valved commanded on and with it commanded off, using a scantool, and the v meter replacing the valve.
Sorry, I'm just trying to understand what is going on here. The wire diagram looks pretty simple, so I might not be understanding something. It seems like the computer is grounding the circuit no matter what the command is.
Example, I don't understand how there could be an open wire if I have 12v.
So you have the solenoid unplugged and one of the voltmeter leads on one wire and the other lead on the other wire in the connector?
If so, you should read 0v with it off and 12v with it on
Nandor69 wrote: So you have the solenoid unplugged and one of the voltmeter leads on one wire and the other lead on the other wire in the connector?
If so, you should read 0v with it off and 12v with it on
bruce.oliver wrote: If you have ground on the white wire all the time, the wire could be shorted to ground
That's what I was thinking. Or there is something wrong with the pcm. The other thing is that the load pro was showing voltage drop/high resistance on the red/white wire.
I've got the car back again now to figure this one out. I had some incorrect information that I provided earlier on. The voltage drop is on the ground wire. I have 12v when I replace the solenoid but not enough to make my test light shine. I'm confident the voltage drop is on the ground wire. Finding it is killing me though. What are some likely places to look here?
Tutti57 wrote: I've got the car back again now to figure this one out. I had some incorrect information that I provided earlier on. The voltage drop is on the ground wire. I have 12v when I replace the solenoid but not enough to make my test light shine. I'm confident the voltage drop is on the ground wire. Finding it is killing me though. What are some likely places to look here?
X200 is a bulk connector, and the dotted line means all those wires are in the same connector. I don't know for certain, but I think X200 is an eight or ten pin connector that plugs into the body, near the right rear wheel. That same connector will have the fuel pump and fuel tank pressure sensor wiring in it, too.
I've never seen an issue with X200, so my guess would be that you're gonna find a wiring issue within a few inches of the vent valve connector.
