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Check engine light stays on

Tiny
SHERU
  • MEMBER
  • 2006 HYUNDAI SONATA
  • 3.3L
  • V6
  • 2WD
  • AUTOMATIC
  • 110,000 MILES
The check engine light came on and stayed on. The garage connected the computer and said that the fuel mixture was weak. Now they have changed the air flow meter - No change.
The fuel pressure is 3.5 bar(should be 3.8). The car was difficult to start this morning while still at the workshop. Never had starting problems before. This has caused the mechanic to focus on the slightly lower fuel pressure and intends to see If it happens again tomorrow morning with the fuel pressure gauge on at the moment of starting. I have not yet checked the petrol filler can vent. Apparently others have found That to be the problem. Will keep you posted. Although the car is twelve years old it still runs like new and I am quite fond of it. A solution would be much appreciated.
Best,
Sheru
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Thursday, February 14th, 2019 AT 4:15 PM

44 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good evening,

What is the exact code?

Low fuel pressure will cause several codes.

https://www.2carpros.com/articles/how-a-fuel-pump-works

Let's start at the beginning with the code.

Roy
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Thursday, February 14th, 2019 AT 4:20 PM
Tiny
SHERU
  • MEMBER
  • 4 POSTS
P0171
P0174
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Monday, February 18th, 2019 AT 2:39 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Thank you.

Low fuel pressure will cause these codes.

As you stated, please check the fuel pressure and report back. If the pressure is off even 5 lbs. It will set this code as not enough fuel is being delivered to the fuel rail.

Also, check for any vacuum leaks.

Roy
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Tuesday, February 19th, 2019 AT 4:37 AM
Tiny
SHERU
  • MEMBER
  • 4 POSTS
Thank you Roy.
The pressure is off by 0.3 bar (3.5 as opposed to 3.8) which is 4.3 psi under the recommended.
However, the light suddenly went out!
I expect it will come back on any minute.
Sheru
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Thursday, February 21st, 2019 AT 1:03 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Yes, it will definitely come back on.

Computers cannot fix themselves yet.

Roy
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Thursday, February 21st, 2019 AT 10:11 AM
Tiny
SHERU
  • MEMBER
  • 4 POSTS
Doesn’t solve my problem.
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Thursday, February 21st, 2019 AT 5:05 PM
Tiny
JJMIZIN
  • MEMBER
  • 5 POSTS
  • 2006 HYUNDAI SONATA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 43,300 MILES
I own a 2006 Hyundai Sonata V6. I have taken it to several dealerships because the check engine light had come on. During 3 of the inspections, they found Code P0456 and changed the following parts: Canister Valve, Purge Valve and Air Flow Meter. Is there something that they are missing? The light seems to be an ongoing issue and just came back on. Please, any info as to what the core issue could be, I'd appreciate it. I've got an appointment to take it, once again, back to the dealership for service. It would be nice to ask them to check for something specific.
Thanks much. John
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
FLEXY5
  • MECHANIC
  • 512 POSTS
Do you know if they have done a smoke test on it? It's a test that pumps smoke into the system which should be sealed. Wherever the smoke escapes is the leak. It shouldn't be a guessing game. The other thing to look for is the gas cap. If the vent on the cap is faulty it will set off the light. Find out about the smoke test though and post back any further info on their diagnostics if you can. Thanks
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
JJMIZIN
  • MEMBER
  • 5 POSTS
I do not think that they've performed a smoke test. It seems like they just hook the car up to their computer and whatever code their computer gives them, they work off of. I'll ask them to perform the smoke test and also ask about the gas cap vent. Hopefully, they'll be able to figure out what the real issue is. My next appointment is on Wednesday March 5th. I'll post an update after and let you know what the outcome is. Thanks again. John
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
JJMIZIN
  • MEMBER
  • 5 POSTS
They came back with the same code: P0456 and replaced the canister valve again. They said they did a smoke test and that a leak came from this part. They also checked the gas cap vent and said it was working properly. When my wife picked up the car today and started to drive the car from the dealership, the light came back on. There has got to be something that they're not seeing, doing, or checking. It's getting really fustrating. Please any additional help would be appreciated. Thanks.
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
SHAJRAH
  • MEMBER
  • 2 POSTS
  • 2006 HYUNDAI SONATA
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 38,000 MILES
I had my car detailed and specifically told the detail shop not to clean the engine out of fear that the moisture/water might get into the electrical system and cause problems. Well the idiots did and now my check engine light is on and the car runs very rough. It feels like it is going to stall. I took it to a mechanic friend of mine and he said that probably some moisture/water got into the plugs and wires. He told me to drive it for a few days and that it might dry out, otherwise replacing the the wires should take care of it. What do you think?
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
FLEXY5
  • MECHANIC
  • 512 POSTS
Most purge valves are electromechanical, meaning they require voltage to open a solenoid. Most of the time they are drop voltage 5vref. I'm beginning to wonder if maybe you have a short that is holding open the purge valve, or maybe the computer is getting a false signal from a monitoring sensor and commanding the solenoid to stay open. Since they have replaced the valve twice and it doesn't even make it home before it bums out again, the problem is not the canister valve. They have determined the symptom and addressed the system. They can identify the component, now they just need to find the cause. Something else is wrong and you need to have them look at the bigger picture. My suggestion would be to take it back and tell them you don't want it back until it is completely fixed. And make sure that they drive it for two complete drive cycles (complete warm up to complete cool down is one drive cycle).
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
ZACKMAN
  • MECHANIC
  • 4,202 POSTS
Does the problem still exist? Is the check engine light still ON?
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
JJMIZIN
  • MEMBER
  • 5 POSTS
I've called hyundai customer service. They said that they would look at the car's history and call the dealership that's been working on my car. They said that they would work with the dealership to solve the problem. When I take the car back this Friday, I'll definitely tell them what you told me. Hopefully, they'll be able to figure out what the cause is and fix the problem this time. Thanks again for your help and I'll keep you updated as this gets resolved. John
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
SHAJRAH
  • MEMBER
  • 2 POSTS
Yes the check engine light turned off and the car is running like new again. Thanks
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
JJMIZIN
  • MEMBER
  • 5 POSTS
They finally found the real problem. When we first purchased the car, it needed a new fuel pump. They took two weeks to install it. While installing it, they did not set the O-Ring correctly on it, so the leak was from a gap in the O-Ring. It took several attempts and a call to customer affairs to get it right. We've had the car for more than a week now and the check engine light has remained off. Thanks for all your assistance with this. I'll definitely come back to this site if I need any more info or help. Thanks much, your help was appreciated. Sincerely, John.
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
ZACKMAN
  • MECHANIC
  • 4,202 POSTS
OK. Have a good day.
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
MIKEL43
  • MEMBER
  • 1 POST
  • 2006 HYUNDAI SONATA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 87,000 MILES
My check engine light is on just had o2 senser repalced and used engine put in 2 months ago with 29000 on it
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Get the computer rescanned for code/s and get back with it if any present
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)
Tiny
DARYLWW54
  • MEMBER
  • 1 POST
  • 2006 HYUNDAI SONATA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 80,000 MILES
Location of check engine light censor
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Thursday, February 21st, 2019 AT 5:07 PM (Merged)

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