I have the P1451 code on a 2000 Explorer 5.0, Evap Vent Solenoid Circuit Malfunction. First of all, is there any difference between a "Purge" solenoid and a "Vent" solenoid?

I measure 23-25 inches of vacuum at the evap purge solenoid at idle located under the battery.

With the key OFF I measure 0V on both of the wires on the harness vs. battery ground.

With the key ON/engine OFF I measure 12.3V on the red wire when terminated to battery ground, and 0.11V on the green/black wire when terminated to battery.

I measured 31.8 ohms resistance on the solenoid, and after I went to AutoZone for a replacement HERE I measured 31.0 ohms resistance across this new solenoid. I have seen a question regarding resistance needing to be in the 50-60 ohm range for this solenoid, but nobody has confirmed what it should be for sure.

Changes made to date include all of the aforementioned measurements, replacement of the purge solenoid and then pulling the battery cables to clear the codes. Upon the 2nd startup the code has returned, this occuring without any driving to speak of just starting and running in the driveway.

1. Do any of the measurements that I have taken appear to indicate a problem with any component or wiring?
2. Is the purge solenoid the right component to be troubleshooting?
3. Is there a vacuum or maybe fuel tank pressure situation that could be causing this issue?
4. What should the solenoid resistance measure? Any chance AutoZone sold me a junk part?

I would appreciate any insight you may have. I can't find any issues that I can point to and confirm that they are related or the root of this trouble code.

 

Update: I figured out there is a difference between the "Purge" solenoid valve and the "Vent" Solenoid. The purge is located under the battery tray and has a vacuum line on it. This is the valve that is available from AutoZone and is not related to the P1451 code.

The vent solenoid is located above the spare tire on an explorer with the charcoal cannister. The wiring runs above the left shock absorber and is attached to the frame crossmember with a press in clip.

For some reason the factory installed the fasteners for the charcoal cannister cover from the top with the nutserts installed on the cover instead of the frame. This makes it a complete pain to take the cover off, and in fact I gave up and didn't remove it at all. There is just enough room to get to the solenoid at the front of the plastic cover, you can see it through a hole in the cover. Mine is rusty, and neither wiring lead was connected to the solenoid, they were both broken off about 1/4" outside of the connector. I had to remove the pins from the connector and recrimp the wires into the pins and then reinstall into the connector.

I measured the voltage across the two wires with the ignition in the ON position/engine OFF, one wire was 12.1V and the other was 0.05V, for a differential of ~12V. The resistance across the vent solenoid was 56ohms, which agrees with the 50-60ohm target that I've read again on other threads.

I unhooked the battery and then went for a test drive. About 5 minutes in I shut off the ignition and restarted. The Check Engine light came back on. I'm not sure where to go with this now since the solenoid appears to have the correct resistance and the wiring has the correct voltage. I'm guessing that as the voltage changes to the solenoid the position is not changing correctly, resulting in an invalid resistance across the solenoid.

Any thoughts?

 

Hmmm, quiet crowd. I dropped in to the local junk yard and picked up another Vent Solenoid to drop in place of my original. This one is from an F150, but it looks exactly the same and the resistance is a similar 55ohms arross the terminals. I still get a differential 12.1V across the terminals on the wiring harness. Once again after resetting the code by popping the negative battery cable I went for a drive, shut it down, and restarted to see the check engine light come back on right away. This is a code that only turns the check engine light on after two failures, so this tells me that it's failing both times I startup after clearing the codes.

Short of taking it to the stealership I have no other ideas. I have voltage, and two different solenoids with ~55ohms of resistance are still resulting in the P1451 code. Help!

 

I checked the voltage at the vent solenoid and with the key on/engine off I found 11.6V on one wire, and 0.04V on the other wire. When I turned on the engine I measured 14.4V on the wire that had been 11.6V, and 0.08V on the wire that had been 0.04V. The differential is increasing by about 2.8V when the engine is started.

I still measure 55ohms across the solenoid.

 

I checked all of the fuses on the side of the dash as well as in the power distribution block. They are all good, but I am missing #5 Data Link Connector 10A, and #36 EATC Memory, CD, Rear Integrated Control Panel, Memory Seat, Message Center 7.5A. I don't know what #5 is really referring to, but I will get a fuse in there before I try anything more.

 

I installed fuses in both #5 and #36 and that didn't make a difference. I cleared the codes and the light came back on after the second restart. I could use a link to a service manual or other ideas if anyone has them, please.

 

FIXED!

So I have been on the correct path with the Vent Solenoid at the rear of the vehicle. My problem is actually as posted before, the wiring to the Vent Solenoid was broken and after getting a short piece of connector from the pick-a-part along with a replacement Solenoid I fixed the issue. I didn't realize that the issue was fixed because I was still getting a code causing the check engine light to come on after 2 starts, and I assumed the code was still present. Today I stopped by the local Advanced Auto and the P1451 code was gone, but now I had a P0443 instead, a code for the Purge Solenoid. This had not been there before, and since I just replaced that solenoid with a new unit from AutoZone I was very suspect. Upon returning home I found the Purge Solenoid was not connected, so at some point I had measured voltage and resistance but forgotted to connect it back at the same time I was learning about the Vent Solenoid, and I never made the connection, literally.

Long story short, my root cause was the wires to the Vent Solenoid were broken and the code was eliminated by fixing the harness. It just took me extra long because I am an idiot who forgot to plug stuff back in. This one is closed, and I hope it helps someone else with these codes.

 

Nice, thank you for the update!

-Rod