Check engine light

Tiny
TATSUKAN1
  • MEMBER
  • 2012 CHEVROLET SONIC
  • 40,000 MILES
My check engine light came on a couple weeks ago and I had the codes read by Autozone. The guy that I had change my oil said that the codes I was getting were most likely caused by a faulty gas cap, so I bought a new one. After a few days, the light was still on so I went to a mechanic to get their opinion and the mechanic said that it was probably one of two different solenoids. He cleared the codes for me and suggested that I pull out the more easily accessible solenoid and check it by trying to blow through it. Based on what the mechanic told me the first solenoid should be fine so I set up an appointment for this Friday so that he could check the other solenoid to find wherever the leak was coming from. But my question is, could the first guy have been right about the gas cap? Because my check engine light has been off for almost a week and I have driven on it for over one hundred miles. How long should it take the light to come back on if there is still a problem?
Monday, September 25th, 2017 AT 9:00 AM

3 Replies

Tiny
STEVE W.
  • MECHANIC
  • 15,446 POSTS
Without knowing the exact codes there is no way to answer this question. There are literally hundreds of codes and they can be set by virtually any part of the vehicle.
For instance a P0455 code is a large leak detected by the EVAP test system. A lot of places will say "That's a bad gas cap" but it actually can be any part of the fuel system or EVAP equipment that caused it. Could have even been that the car was running the test and the bumps caused a fault to appear. The system then ran the test again once the conditions for it were correct and it passed.
Virtually impossible to know without the codes.

Code wise there are:

P0___ powertrain codes
P1___ powertrain codes, which are manufacturer specific so what a P105 means for Ford isn't the same as it is for GM
P2___ generic codes
P3___ generic codes.

Plus there are

B____ Body Codes
C____ Chassis Codes
U____ Network Codes.

Those are only the OBDII codes.
Most makers also have their own specific codes that a common OBDII reader cannot read as well.
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Monday, September 25th, 2017 AT 11:10 AM
Tiny
TATSUKAN1
  • MEMBER
  • 2 POSTS
I could not remember what the codes were until you mentioned the P0455 code and that was definitely one of them. There was another code that read with it but I cannot remember what it was exactly. If I remember correctly they were both related to the same sort of thing. I would get them reread so I could tell you exactly but like I said, the mechanic cleared the codes and they have not come back on yet. I am just wondering how likely it is that it will come back on and how long it might take to do so? I have an appointment to take my car in on Friday but I do not know if I really need to or not.
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Tuesday, September 26th, 2017 AT 8:51 AM
Tiny
STEVE W.
  • MECHANIC
  • 15,446 POSTS
EVAP codes can be a pain. The tests only run under specific conditions. The easiest thing would be to just have them look at the system monitors. They will tell you if the various tests have run or not. If the EVAP has run and you don't have a light you are okay. If it has not run then?
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Tuesday, September 26th, 2017 AT 11:24 AM

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