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2005 Platinum CTS V-Headers+3in pipes
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Discussion Starter #1
SO i failed inspection on thursday because my check engine light would not come on while the car started up. its acting weird sometimes i see the light, then it goes away before all the others cycle through and sometimes it just doesn't turn on at all. Specifically, my car's evaporation system was not ready to read data so i failed that. and I failed the "bulb check". Last week we had the differential replaced on the last day of the warranty. I'm assuming they disconnected the battery and wiped out all the sensor data, but why is the check engine light not being consistent?



so the question is how many miles do i have to drive to get my check engine light to go back to normal..
 

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See you in the funny papers
04 CTS-V, 05 STS, 07 SRX- All sold :(
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26,239 Posts
I think this qualifies as the first time in the history of the Internet that a thread was made asking how to get the check engine light to come ON. :lol:

I have no idea what the problem might be. Check with your Dealer.
 

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Premium Member
2005 CTS-V
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8,363 Posts
My 1997 Chevy suburban almost failed inspection once because the Check Engine Light did not come on when the ignition was turned on. It turned out that the inspection tech had set the parking brake which was not part of his normal routine on vehicles with automatic transmissions. On this particular vehilcle setting the parking brake deactivates certain circuits including the CEL and the DRLs.
 

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2004 CTS-V with 2 carseats in the back and a f'ing minivan
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607 Posts
All I can report is my experience with my DD which is a Merc Sable. The memory wire for the computer runs through the horn circuit and the horn circuit was damage at some point during an accident before I bought it. If you press the horn it blows the fuse. I didn't really care about the horn because I know universal driver sign language anyway.:dflip: However when I went to the smog place to get the car checked it wouldn't show anything because they cut the car off and hook up the port and then turn the car back on so essentially it had no memory every time you turned it back on. The solution was to put the fuse in and just not press the horn while I drove it around. I waited about a week before I went back but I put a lot of miles on in a week so it could take you longer to reload the data in your car. I know none of this probably helps but since nobody else was responding I would at least give you what I know. Good luck
 

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Cadillac Technician
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11,051 Posts
The V is kind of a unique beast when it comes to this issue and here is why.

Years ago after OBD-II came out GM kind of changed the power cycle of the PCM. Nowadays there are lots of self tests that run after the engine is shut off. The PCM power mode keeps the logic working for a while after you power down the car.
GM only turns the MIL on (malfunction indicator lamp) once on power up during each waking event. Basically this means that if you turn the key on in the morning then the light will be on and as soon as you start the engine it will go out. Then if you turn the key off and back on you won't see it light up, because the PCM is still awake so it is not required that it come on.
The V takes a long time to go completely to sleep and reset this so the light will come on during the next ignition cycle.

If they use an emissions testing station like I use, the tester tells you to turn the key on and off several times during the test, the V may not like this and it will keep the light off because the PCM is still doing stuff. In order to successfully check the operation of the MIL they may have to leave the key off for several minutes.

If you see the MIL light up, like after sitting overnight, and they fail it for not coming on it is because they don't realize this car is so picky.
It may be hard to explain this to the guy doing the test, but let the car sit and take him out and show him.
I'm not sure if I can find any technical documentation to back this up that you can show him, but that is what is going on from what I see you saying.
 

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Premium Member
2005 CTS-V
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Thanks - that is really good to know. If nothing else, I may print your post and keep it my glove box.
 

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Registered
2005 Platinum CTS V-Headers+3in pipes
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3,012 Posts
Discussion Starter #7
thanks ewill3rd for that explanation.. I'm glad its a normal problem that other people have seen. Can the dealer do anything for me? I might bring it in on Monday morning but like i said my warranty is up so I'm not just going to hand it over.
 

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Cadillac Technician
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11,051 Posts
I found this excerpt, but it doesn't explain the power cycle like I was talking about.
You can do this on almost any car but most cars have a PCM that goes to sleep in less than 1 minute.
For some reason the CTS-V is more picky.
There is no "fix" this is just the way it is. It just needs to be retested by someone with patience.

The MIL indicates that an emissions related fault has occurred and vehicle service is required.

The following is a list of the modes of operation for the MIL:

• The MIL illuminates when the ignition is turned ON, with the engine OFF. This is a bulb test to ensure the MIL is able to illuminate.

• The MIL turns OFF after the engine is started if a diagnostic fault is not present.

• The MIL remains illuminated after the engine is started if the control module detects a fault. A diagnostic trouble code (DTC) is stored any time the control module illuminates the MIL due to an emissions related fault. The MIL turns OFF after three consecutive ignition cycles in which a Test Passed has been reported for the diagnostic test that originally caused the MIL to illuminate.

• The MIL flashes if the control module detects a misfire condition which could damage the catalytic converter.

• When the MIL is illuminated and the engine stalls, the MIL will remain illuminated as long as the ignition is ON.

• When the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition is cycled OFF and then ON.
 

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2005 Platinum CTS V-Headers+3in pipes
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Discussion Starter #9
Thanks again, Ewill3rd... im just going to print these explanations out and tell the DMV tech that the dealer gave me this as an explanation.. its still acting crazy even after letting it sit for 20mins.. hopefully a few more miles will cure it..
 

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04 V
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105 Posts
i had exactly the same thing happen to me. failed because some of my monitors werent ready. i tried going through the driving cycles i searched online but dont even waste your time, since youre in jerzey you can drive 45 days with your failed inspection sticker so just drive the car for a week and go back, thats what i did and it passed after a week
 
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