How do I determine if someone disabled my service engine light?

Tiny
DAEUP
  • MEMBER
  • 2002 GMC SIERRA
  • 127 MILES
I just bought my truck and on the way home, the "service engine soon" light came on. Checked it the next day and it was code 0420 (either the cat or the o2 sensor I believe. Anyway, took it back to the dealership, they cleared it, and it's been two days since and it hasn't come back on. They have done a few other shady little things and I wouldn't put it past them to somehow disable the light to keep it from coming back on. Where do I look and what do I look for to determine if they did indeed disable the light? Thank you in advance for your help.
Wednesday, December 7th, 2011 AT 5:16 PM

7 Replies

Tiny
DRCRANKNWRENCH
  • MECHANIC
  • 3,380 POSTS
There is not much of a way to be sure except to remove the instrument cluster and check for the connection.
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Wednesday, December 7th, 2011 AT 5:23 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
I don't think the dealership would do such a thing
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Wednesday, December 7th, 2011 AT 5:24 PM
Tiny
DAEUP
  • MEMBER
  • 2 POSTS
Thank you for your answer DrCranknWrench. And Rasmataz, I understand why you'd say that, but you'd be surprised. I have been. They are looking pretty shady at this point. If I hooked a scanner up to it, would it tell me anything? Or any other telltale signs? Thank you so far.
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Wednesday, December 7th, 2011 AT 5:55 PM
Tiny
DRCRANKNWRENCH
  • MECHANIC
  • 3,380 POSTS
I will say that it would be a tremendous pain to disconnect the check engine light. If you ever took it to another dealer and had it fixed they would get busted and it just would not be worth the effort it takes to dis-connect the CEL.
However, I am not saying it does not happen. Is this some long on-going fued over getting something fixed that has gone on so long that it might get to that point?
I don't know for sure if a scanner would pick up a CEL, but I have seen some that do. Even this is not always 100%. That is why I mentioned the actual visual inspection of the connector. It can be dis-connected elsewhere, but with the same trouble as per the number of connectors that would have to be dis-connected. When these start getting pulled off, things start going wrong with engine performance.
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Wednesday, December 7th, 2011 AT 6:27 PM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
TY Doc-sure appreciated-I don't think I have the time to cut wires and removing the bulb on it-Been in this business too long

Can you imagine if he goes somewhere else and willing to pay to have it checked and it turns out missing-. Things are gonna hit the fan and its not ours-lol
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Wednesday, December 7th, 2011 AT 10:00 PM
Tiny
CJ MEDEVAC
  • MECHANIC
  • 11,004 POSTS
ALL YA'LL?

SHOULDN'T THAT PUPPY COME ON WHEN YOU TURN THE KEY TO "ON" OR WHILE YOU ARE CRANKING THE BEAST?

VERIFYING THE BULB WORKS, PRIOR TO SLEEPING UNTIL A PROBLEM OCCURS?

RAZ---I HAVE 1ST HAND SEEN A STEALERSHIPS DO WORSE!

THE MEDIC
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Friday, December 9th, 2011 AT 3:08 AM
Tiny
HOMER1967
  • MECHANIC
  • 875 POSTS
Just turn on the key, no crank if the light works it will come on with the key.
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Friday, December 9th, 2011 AT 3:23 AM

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