How JustAnswer Works:

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

Ask johnt Your Own Question

johnt
johnt, ASE Certified Technician
Category: Chevy
Satisfied Customers: 85
Experience:  27 years experience foreign and domestic
6607327
Type Your Chevy Question Here...
johnt is online now
A new question is answered every 9 seconds

I have a 2005 Chevy Silverado that shows a PO455 code. I removed

Customer Question

I have a 2005 Chevy Silverado that shows a PO455 code. I removed and re-tightened the gas cap but the code didn't go away. Does the need to be cleared? If so, how do I clear OBD code?
Submitted: 5 years ago.
Category: Chevy
Expert:  johnt replied 5 years ago.

The gas cap is not the only possible cause , this code shows a large evap system leak.

Other potential causes are as follows.

  • Fuel filler cap is very loose, missing or the wrong part
  • Fuel tank, fuel filler neck or fuel sending unit 'O' ring is leaking
  • Fuel tank pressure sensor is damaged, disconnected or it failed
  • Fuel tank vapor line(s) is clogged, damaged or disconnected
  • Purge valve vapor line is clogged, damaged, or disconnected
  • Purge solenoid is not opening (it may be damaged or sticking)
  • Vent solenoid is not closing (it may be damaged or sticking)
  • PCM has failed

If in fact the gas cap was the problem the code will reset itself after the next test cycle

runs . Here are the parameters for the test to run.

 

  • At least 17 hours have elapsed since the last drive cycle met the test conditions.
  • MIL is off.
  • No Emission related DTC's are present.
  • Accessories turned off (A/C, fan motor, headlights and rear window defroster).
  • BARO signal over 74 kPa.
  • Battery voltage between 10-18v.
  • ECT and IAT signals between 39-86ºF.
  • Difference between the ECT and IAT signals at startup less than 14ºF/
  • Estimated ambient temperature at the end of this drive cycle between 39-86ºF.
  • Fuel level between 15-85%.
  • Vehicle speed less than 75 mph.

You can reset with a scan tool , the large parts chains will usually scan and clear

the codes for free. Also check the o'ring on the gas cap for cracks.

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:

 
 
 
  • I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money. Todd L Rochester NY
< Last | Next >
  • I was having a terrible problem with the wheel bearings on my 98 Chevy Cavalier and I suspect that using this website saved me plenty of time and money. Todd L Rochester NY
  • 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!!!! Alex Los 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. GP Hesperia, CA
  • I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, 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. Esther Woodstock, 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. Robin Elkton, Maryland
 
 
 

Meet The Experts:

 
 
 
  • Tim's Auto Repair

    mechanic

    Satisfied Customers:

    7641
    Have owned a repair shop for 25 yrs.
< Last | Next >
  • http://ww2.justanswer.com/uploads/TI/tim37857/2011-10-28_23053_S6301814.64x64.JPG Tim's Auto Repair's Avatar

    Tim's Auto Repair

    mechanic

    Satisfied Customers:

    7641
    Have owned a repair shop for 25 yrs.
  • http://ww2.justanswer.com/uploads/DT/dt69nova/2012-6-15_234154_pic1.64x64.jpg Dave Nova's Avatar

    Dave Nova

    Chevrolet Technician

    Satisfied Customers:

    6870
    ASE Master Certification. GM World Class Certification
  • http://ww2.justanswer.com/uploads/ggrote1/2009-06-27_031011_me.jpg Gary's Avatar

    Gary

    Chevy Technician

    Satisfied Customers:

    5404
    15 years GM master tech
  • http://ww2.justanswer.com/uploads/testedtuff/2009-09-26_170108_pictures.jpg John's Avatar

    John

    Master A.S.E Automotive technician

    Satisfied Customers:

    4071
    A.S.E MasterTechnician A1-A8 w/L1,38 years experience General Motors Master Technician
  • http://ww2.justanswer.com/uploads/RO/rodcuda/2011-7-25_224114_Donhoff1.64x64.JPG Neal's Avatar

    Neal

    Chevy Mechanic

    Satisfied Customers:

    2306
    Shop Owner and Mechanic on multiple makes.
  • http://ww2.justanswer.com/uploads/goodwrench9124/2008-11-09_220838_dscf0007.jpg goodwrench9124's Avatar

    goodwrench9124

    ASE Certified Technician

    Satisfied Customers:

    2041
    Ase Master Certified, GM Master Certified Tech. Awarded GM Top performer, Hybrid certified
  • http://ww2.justanswer.com/uploads/DR/drivefast1971/2012-1-12_172422_0009051tQKh.64x64.jpg Ron Z.'s Avatar

    Ron Z.

    - Chevy Tech -

    Satisfied Customers:

    1912
    18+yrs experience. State Inspector and Chevy Diagnostics
 
 
 
Chat Now With A Chevy Mechanic
johnt
johnt
manager
14 Satisfied Customers
27 years experience foreign and domestic