tech2

would be nice to know what code was setting


the tcm-batt fuse in the under hood fuse block supplies power on the red/white wire at all times to the vent solenoid. the white wire is grounded by the ecm to close the normally open solenoid.


if you provide grd on the white wire you should hear the solenoid click closed and thunk open when the grd circuit is open.


I back probe the plugged in connector with a t-pin and connect a jumper wire to grd. if you hear nothing, unplug the connector and test the red/white wire with a test light to grd, not a dvom.

69impalaconvharv

Tech 2; Thanks for the expanded info on checking out the evap solenoid. I tried responding to the email you sent to me on this problem, but it kicked it back saying it was undeliverable. I hope to check it over the long weekend. I am guessing that is what the problem is with my truck. Do you know if part houses typically have a bi directional scan tool or is a dealer typically the only one that has such a scan tool? Is there much difference in the replacements? Rock Auto has several available with a wide range of prices. Any suggestions on which to get if that turns out to be the problem? Thanks for your valuable information.

69impalaconvharv

69impalaconvharv

Hi Tech 2:

I got the time to put my Silverado truck on the lift today and check things out. Here is what I found: The evap solenoid cycles as it should when grounded, so that tells me there is a ground circuit problem. When I unplugged the connector and put a test light across the terminals, it would not light, further confirming that there is a ground circuit problem. If one end of the test light is connected to the red/white wire from the connector and the other end is grounded, it lights. That also tells me the power supply is good but the ground circuit (white wire) is not. With no access to the electrical schematic, I don't know if the ground circuit (white wire) is switched or if the power supply (red/white wire) is switched. Finally, I checked the resistance from the white ground wire to the ground and had 5.3K ohms. Saturday I will stop back at the parts house and ask them to tell me what the code number is if there scan tool is a bi-directional unit. Can you shed some light on how to proceed or check out the ground circuit? Thank you for all your help. It is very much appreciated.

Harv

tech2

the ecm grds the circuit. without a scan tool to command the solenoid closed; the circuit will not show grd.


post the dtc when you get it

69impalaconvharv

Tech 2: Per your request I had the code re-read on my 2009 Silverado 1500 and it was PO 442. They tell me it is the code for a small leak of .020" or less in the evaporative emissions system. My dealer said I would have to get a smoke test ($60) to find the problem since the gas cap was replaced and the evap solenoid tests good. Any other things I should check, or just have the smoke test done and go from there? Thanks.

Harv

tech2

smoke test is the next step. I have seen leaks at the filler neck. the metal neck rusts and the cap can't seal it. $60 to perform and locate an evap leak is a very good price.

drymocke

In my 2007 Suburban LTZ the check engine light came on about 2 years ago. I took it to Auto Zone at that time and according to them the code pointed to the evaporative solenoid. I have been ignoring it for 2 years but now need to pass CT emissions testing, so I will be getting it repaired. My fear is, like most “check engine” light problems, it will return within in a week of supposedly being fixed by the dealer. I think for this problem I may take it to a local mechanic, who stands behind his work. I will let you know how it turns out.

djvaughn@outlook.com

Yes there is a gas cap code.

djvaughn@outlook.com

I just ordered one myself for my 2006 Tahoe. Hope this fixes it as the check engine light comes on and off for the last 6 months and code says its the gas cap.

Shari Heagle Reif

​​​​​​ There certainly is a code that says check gas cap. We're dealing with this and our 2015 chevy malibu. The dealer pulled the code, smoke tested the system(pretty sure the dealer knows how to use a smoke machine) and tested the cap. Everything tests out fine, but the stupid light is still on. Driving me bonkers.