GMC

GMC Troubleshooting Questions? Ask a Mechanic for Answers

Ask an Expert,
Get an Answer ASAP!

GMC

I have a 1999 GMC Sierra. I have driven it over 300 miles

Customer Question
yet the Sec Air system...
I have a 1999 GMC Sierra. I have driven it over 300 miles yet the Sec Air system and Evap system Mon - monitors read incomplete. there are NO hard codes. I did recently change the knock sensors. How can I get these cleared so I can get a California smog cert
Submitted: 1 year ago.Category: GMC
Show More
Show Less
Ask Your Own GMC Question
Answered in 4 hours by:
3/3/2016
GMC Mechanic: JFN1, ASE Certified Technician replied 1 year ago
JFN1
JFN1, ASE Certified Technician
Category: GMC
Satisfied Customers: 4,832
Experience: GM Master Technician
Verified

EVAP monitor will only run after a cold start. The vehicle has to be completely cold, such as sitting overnight, before the EVAP monitor will even attempt to run. Then, it only runs under certain circumstances.

The secondary air monitor also only runs under very specific conditions. I'll list them here:

No MAF DTCs

  • No MAP DTCs
  • No IAT DTCs
  • No ECT DTCs
  • No TP Sensor DTCs
  • No HO2S DTCs
  • No VSS DTCs
  • No system voltage DTCs
  • No Fuel Trim DTCs
  • No Misfire DTCs
  • No CCP DTCs
  • MAF is less than 25 grams per second
  • Engine load is less than 34 percent
  • Power Enrichment Mode is not active
  • DFCO (Decel Fuel Cutoff Mode) is not active
  • Convertor Over Temperature not active
  • Engine run time after Closed Loop is more than 20 seconds
  • Air/Fuel Ratio is 14.7:1
  • Fuel Trim counts between 124–132
  • Engine speed above 550 RPM
  • ECT is between 80–107°C (176–225°F)
  • System voltage is more than 11.7 volts
  • IAT is more than 2°C (36°F)

Once all these criteria are met, the PCM software is programmed to pick an appropriate time to run the AIR pump. While GM does not tell us exactly when this occurs, I have noted it happening at low speeds, around 35 mph, at steady throttle. When the AIR pump comes on, the PCM is expecting to see oxygen sensor readings drop to near zero.

EVAP is tougher. Cold start, and normal (not aggressive) driving. The test will run about ten minutes into the drive cycle. If you shut the engine off and restart it, it won't try to test again until you have a cold soak.

It's not a matter of miles, it's a matter of getting just the right conditions. And while I don't know the CA requirements, I know that in my state and many others, you can pass a smog test with two readiness monitors that are not ready on a 1999 car or truck. Do you happen to know what the threshold is in CA?

Ask Your Own GMC Question
Customer reply replied 1 year ago
Thank you for the reply. unfortunately, it does not move me forward. I have done about 50 cold starts in the morning driven the car and still nothing. And just an fyi...in CA I can have a smog test on a 1999 or older vehicle with only the evap monitor inc.. if a car is 2000 or newer no incompletes. this was a new rule implemented at the beginning of 2016.Again I appreciate your response, but if you have no other thoughts please put this question back into the open form so hopefully someone has had a similar issue and can guide me home.
Thanks
GMC Mechanic: JFN1, ASE Certified Technician replied 1 year ago

I understand. That's good info to know about CA emissions, I didn't know they had tightened the standards.

I have seen conditions where the PCM will not perform readiness testing due to a logic lockup. It's worth trying to resolve: disconnect both battery cables from the battery, and hold them together for several seconds. This clears volatile memory, and will cause the PCM to restart with a baseline strategy.

Other times, I have performed PCM programming, to update the software, and that seems to get the PCM going again, too.

GM has a book that outlines various readiness testing procedures for different models. I am trying to put my hands on it, but have so far been unsuccessful. Let me work on this a bit before you bail on me. I like a challenge.

:)

Ask Your Own GMC Question
Ask JFN1 Your Own Question
JFN1
JFN1
JFN1, ASE Certified Technician
Category: GMC
Satisfied Customers: 4,832
4,832 Satisfied Customers
Experience: GM Master Technician

JFN1 is online now

A new question is answered every 9 seconds

How JustAnswer works:

  • Ask an ExpertExperts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional AnswerVia email, text message, or notification as you wait on our site. Ask follow up questions if you need to.
  • 100% Satisfaction GuaranteeRate the answer you receive.

JustAnswer in the News:

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
JustAnswer.com...has seen a spike since October in legal questions from readers about layoffs, unemployment and severance.
Web sites like justanswer.com/legal
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

What Customers are Saying:

Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help.

Mary C.Freshfield, Liverpool, UK

This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!!

AlexLos Angeles, CA

Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult.

GPHesperia, CA

I couldn't be more satisfied! This is the site I will always come to when I need a second opinion.

JustinKernersville, NC

Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around.

EstherWoodstock, NY

Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know.

RobinElkton, Maryland

He answered my question promptly and gave me accurate, detailed information. If all of your experts are half as good, you have a great thing going here.

DianeDallas, TX

< Previous | Next >

Meet the Experts:

Gm Tech (Cam)

Gm Tech (Cam)

GMC Mechanic

1,696 satisfied customers

GM Grand Master Technician 2007. 14 year experience.

Gary

Gary

ASE Certified Technician

1,557 satisfied customers

GCM master tech over 25 years

Dave Nova

Dave Nova

GMC Technician

929 satisfied customers

ASE Master Certification. GM World Class Certification

Chris (aka-Moose)

Chris (aka-Moose)

GMC Technician

583 satisfied customers

16 years of experience

Ron Z.

Ron Z.

- GMC Tech -

259 satisfied customers

18+yrs experience. State Inspector & GMC Diagnostics/Repair

George H.

George H.

ASE MasterTechnician

227 satisfied customers

15+ Years ASE Master Technician with Level 1 Certification

Don - Mo Lurch

Don - Mo Lurch

ASE Certified Technician

218 satisfied customers

GM, GMC, Chevrolet Cert., Heavy Line Mech, Race Shop Owner, Mobile Electronics

< Previous | Next >

Related GMC Questions
Battery will not charge. new battery and new alternator. The
battery will not charge. new battery and new alternator … read more
Cesar Jimenez
Cesar Jimenez
Owner/CEO
Vocational, Technical or Trade School
85 satisfied customers
I have a brand new battery in but my battery level sits at
I have a brand new battery in but my battery level sits at about 11 on the cluster and won't turn on, if I boost it the truck starts and runs normal but if I turn the truck off the truck immediately w… read more
Mechanic01
Mechanic01
1,700 satisfied customers
The battery die over night. The vattery is good I change the
yes the vattery is good I change the vattery and the problem is the same … read more
Chris (aka-Moose)
Chris (aka-Moose)
GMC Technician
Vocational, Technical or Trade School
583 satisfied customers
New battery drains overnight. No but the battery is new. The
No but the battery is new. The same thing happened before the battery was replaced. … read more
AMEDEE
AMEDEE
AUTOMOTIVE TECHNICIAN
Vocational, Technical or Trade Scho
9,105 satisfied customers
I just bought a new battery at autozone and they put it in
I just bought a new battery at autozone and they put it in but the next day when I tried to put 2006 gmc envoy into two wheel drive from auto it just flashes and then moves to four wheel drive high. I… read more
tim37857
tim37857
Mechanic
High School or GED
71 satisfied customers
It will Not start. We tried a new battery- its not the
We tried a new battery- its not the battery, nothing is corroded … read more
David Craig
David Craig
OWNER/MECHANIC
Associates
4,403 satisfied customers
While running sucks all life from the battery. It is a brand
had problems installed battery idled for 1 hour then would not start as battery was dead … read more
kalamykid
kalamykid
Pactor automotive
Vocational, Technical or Trade Scho
97 satisfied customers
Is it normal for a car battery voltage increase after trying
Is it normal for a car battery voltage increase after trying to unsuccessfully start the car and then letting it sit for several moments?… read more
Gary
Gary
ASE Certified Technician
Vocational, Technical or Trade Scho
1,557 satisfied customers
Battery fully charged but when the remote is in proximity
battery fully charged but when the remote is in proximity and brake is depressed nothing happens … read more
GM Bob
GM Bob
Automobile Technician
High School or GED
1,002 satisfied customers
Remote start won't work-changed batteries in remotes and
remote start won't work-changed batteries in remotes and still no luck … read more
GM Bob
GM Bob
Automobile Technician
High School or GED
1,002 satisfied customers
Replaced original battery with an Exide, 18 months later
replaced original battery with an Exide, 18 months later battery will not keep voltage if car sits for 4 days. Replaced battery under warranty from Exide, Worked for another 18 months same problem. If… read more
Todd M
Todd M
Owner
ASE Certification
1,486 satisfied customers
Idle engine. 285000 VVM envoy 2003 XL. Also battery not
This just happened todayhvnt had a chance to do anything as yet… read more
Chris (aka-Moose)
Chris (aka-Moose)
GMC Technician
Vocational, Technical or Trade School
583 satisfied customers
Battery saver light came on. Battery test with the engine
Battery saver light came on. Battery test with the engine off at 12.7 VDC, With the engine running at an idle 15.7 VDC. Trying to locate the issue … read more
Mechanic01
Mechanic01
1,700 satisfied customers
1997 GMC Suburban. Crank, but no start. Battery replaced.
1997 GMC Suburban. Crank, but no start. Battery replaced. Distributor cap replaced. Good spark, but no fuel on spark plug. Dropped gas tank and no power to fuel pump. No voltage across pins 87 and 30 … read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
Will not idle, just noticed that the negative battery cable
Will not idle, just noticed that the negative battery cable is disconnected, also there is a hollow line along the drivers side just under the hood that is broken. Not sure if this is causing the stal… read more
David Craig
David Craig
OWNER/MECHANIC
Associates
4,403 satisfied customers
Battery is dead all of a sudden. symble on dash = Battery
battery is dead all of a sudden. symble on dash = Battery malfunction It's a 2013 Acadia … read more
AZTechBrian
AZTechBrian
ASE Certified Technician & Shop Owner
Vocational, Technical or Trade School
732 satisfied customers
I was cleaning the battery cables and reattached them and
I was cleaning the battery cables and reattached them and now the truck will not start. … read more
Jaybird61
Jaybird61
Master Automotive Mechanic
2,228 satisfied customers
Battery light was on this am but alt is charging. Battery
Battery light was on this am but alt is charging. Battery was dead but is 6 years old. … read more
Pete
Pete
Independent Auto Technician
Vocational, Technical or Trade Scho
138 satisfied customers
Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Disclaimer: Information in questions, answers, and other posts on this site ("Posts") comes from individual users, not JustAnswer; JustAnswer is not responsible for Posts. Posts are for general information, are not intended to substitute for informed professional advice (medical, legal, veterinary, financial, etc.), or to establish a professional-client relationship. The site and services are provided "as is" with no warranty or representations by JustAnswer regarding the qualifications of Experts. To see what credentials have been verified by a third-party service, please click on the "Verified" symbol in some Experts' profiles. JustAnswer is not intended or designed for EMERGENCY questions which should be directed immediately by telephone or in-person to qualified professionals.

Show MoreShow Less

Ask Your Question

x