Trailblazer OBD II Won't Communicate and Pass Smog Check

[Daveroonie]

So I went to have my '07 Trailblazer (4.2l six) smogged (California) and it passed the emissions (barely!) but failed because the OBD II would not communicate with the smog machine. The smog shop had tested and passed an '02 earlier that day so it's not the machine. Also... The tech could see the RPM via the ODB II during the test so it's NOT a bad connector, etc. I drove the Trailblazer only about 8 miles on Sunday and it has sat for a few weeks prior to that.

I checked all fuses (neighbor's suggestion) and they were all good. Any thoughts?

[dvanbramer88]

Glad you found your way over here.

Been thinking about it.

Do you have a scan gauge of your own to test the port yourself?

[navigator]

do both of the 12v power outlets up front work?
If one of them is out, check the fuses again.

[chevycrew]

What do you mean it wouldn't communicate? It was communicating if they saw rpm.

Find the diagram and check for power with a meter.

[Daveroonie]

What do you mean it wouldn't communicate? It was communicating if they saw rpm.

Find the diagram and check for power with a meter.

By "Not communicating" The tech told me it is unusual but he's seen it before. It did NOT give him a "Test Incomplete" error which it sometimes does if you recently changed the battery and all the memory cleared. However, my neighbor is guessing that it is doing just that. This car has been a garage queen for several months. I am going to drive it a bunch soon so I can let it complete all it's internal tests.

I do not have a scan tool but Pep Boys has a sign offering a free scan and I might take it there.

[dvanbramer88]

Word of warning: A lot of autoparts stores employes confuse "service engine soon" which is GM's "check engine light" for an oil life monitor or other maintenance warning. So if you ask and use that term they might tell you they can't read that.

Now i know your check engine light isn't on, just using an example to warn you about stupid people.

[The Roadie]

Where are you? Anywhere near San Diego and I have 2-3 ways to check that out rather than trust the goofs at Pep Boys.

[Daveroonie]

Where are you? Anywhere near San Diego and I have 2-3 ways to check that out rather than trust the goofs at Pep Boys.

Thanks! PM sent.

[The Roadie]

From where you are, the round trip gas is more than getting your own Harbor Freight code reader, especially with all the sales and 20% coupons they throw out there. Consider that, and then you own it.

[Daveroonie]

Thanks for the replies. My neighbor (and some of you) were right. Because it has been sitting or only been driven on short trips about once every 3 weeks it apparently didn't have any current self test results. When it was smog'ed it BARELY passed (HC max allowable-46ppm, HC tested-42ppm).

So I drove it to work (100+ miles one day running around) twice and a 20mi each way trip Sat. Went to the smog place and he hooked it up and lo-and-behold! About half of the self tests read "COMPLETE". The rest now read "INCOMPLETE" (before they read nothing I think). So drove it Monday & Tuesday to work and went back to the smog guy and SHAZAM! All tests read complete. So he put it on the rollers and retested. Passed with flying colors now that it was running in "closed loop" control. HC - 7 ppm! So lack of use was the issue.

(posted in the GMC 4X4 forum also)

[dvanbramer88]

Glad you got it sorted out.