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Old 03-15-2013, 04:34 PM Thread Starter
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Steady Check Engine Light, Help Please!

Recently my Check Engine light came on in my 2006 Chevy Cobalt SS. It seems after the light came on it seems like i've been getting less kms to the tank.

I've looked through my manual for tips and advice to try and remove the warning light but nothing has worked. I have taken my gas cap off and put it back on again in hopes that it was just an unsealed gas cap but nothing has changed. I have used my OBII code scanner to try and get a code but it comes up saying "error". I just bought this car a little over a week ago, it was safetied and etested by the dealer (84,000kms on car). Just curious as to why it seems like it is an emission problem(because of fuel economy) right after passing the etest.

One more thing, the battery was disconnected from the car for a little while before I bought it, could that be why I'm not getting a reading from my scanner? The first time the car was taken for the etest it failed because they couldn't get a reading from the the car's computer or something he said. He drove it around for an hour the next day, took it in and it passed.

Any help would be greatly appreciated!
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Old 03-15-2013, 04:37 PM
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try bringing to autozone? they do free check engine line checks.
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Old 03-15-2013, 05:31 PM
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MPG always drops with a DTC because ECM puts car in default mode. Just like when you first start your car, no sensors are read so no fuel trim is done. Older OBDII readers won't read the Cobalt codes because it needs CANDI protocol.

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Old 03-15-2013, 08:26 PM
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Huh? With any code it automatically goes to default mode? I've never heard of that. Maybe with specific codes. I'd more than bet its an O2 sensor code.

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Old 03-15-2013, 08:56 PM
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woah woah.... cel's can change the way your car drives? i thought it was just like a "hey you messed something up" alert.
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Old 03-16-2013, 05:15 AM
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Quote:
Originally Posted by Coby7 View Post
MPG always drops with a DTC because ECM puts car in default mode. Just like when you first start your car, no sensors are read so no fuel trim is done. Older OBDII readers won't read the Cobalt codes because it needs CANDI protocol.
If the OBDII scanner was made before the chassis initial dates, then the scanner will do a general OBDII scan, not vehicle specific. Ensure that on your plug and play socket pins 4,5,and 16 are not bent or missing, that is vital for communications from Engine Control Module to Scan Tool.

When you first start your car, the CEL lights up and does a quick check of all sensors and solenoids (inputs and outputs), except for the O2 sensors (they require a minimum temp of 600 degrees and time in order to achieve closed loop). Your car is not in default mode, its called "fault" :P

Not saying your wrong Coby7, just thats the information UTi, Wyotech, and technician schools say.

Quote:
Originally Posted by WISHiBOUGHTanSS View Post
woah woah.... cel's can change the way your car drives? i thought it was just like a "hey you messed something up" alert.
Yes, once your car's computer has found a fault or bad reading from one of many sensors it monitors, it goes into what is called Keep Alive Memory. It basically stays in that mode until the problem is fixed, codes are cleared, and the ECM is detecting normal operations. I saw up here about an 02 sensor and that is quite common for today's cars, but dont always rule it out as a first thing. Your vehicle will lose its optimal performance (fuel economy and power) in order to keep that car running, if it were an 02 sensor, it will trigger to spike up the air/fuel mixture from the 14.7 (stoichometer) to (rich). Not saying this is horrible, but it will cause if ignored, serious wear and tear (spark plugs may foul up, flood in combustion chamber, excessive fuel thrown into catalyic converter, there may be more too) on the engine.

Last edited by 5t3alth; 03-16-2013 at 05:33 AM.
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Old 03-16-2013, 08:12 AM
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Quote:
Originally Posted by 5t3alth View Post
If the OBDII scanner was made before the chassis initial dates, then the scanner will do a general OBDII scan, not vehicle specific. Ensure that on your plug and play socket pins 4,5,and 16 are not bent or missing, that is vital for communications from Engine Control Module to Scan Tool..
How old are your textbooks 5t3alth? Pins 4 & 5 although still wired and still have their use on a Cobalt strictly for "ECM". Like I mentioned before, the Cobalt uses the CANDI protocol and this communication is done on pin 6 & 14.




Quote:
Originally Posted by 5t3alth View Post
Not saying your wrong Coby7, just thats the information UTi, Wyotech, and technician schools say..
Uh! you kinda are...

But you were right KAM or Keep Alive Memory is the proper term for default mode. TOmato, tomAto.....Whenever your vehicle falls onto a KAM it sets fault code DTC B1004. If you don't have this code in history car was never in KAM
.
---------- Post added at 11:12 AM ---------- Previous post was at 11:05 AM ----------

Quote:
Originally Posted by money_man View Post
Huh? With any code it automatically goes to default mode? I've never heard of that. Maybe with specific codes. I'd more than bet its an O2 sensor code.
Should have specified Primary codes and only "P" codes type "A" from P0010 to P0199.

Let me check the server and I'll comme back with the descriptive paragraph quote.

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Last edited by Coby7; 03-16-2013 at 08:45 AM.
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Old 03-16-2013, 10:44 AM Thread Starter
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So i'm really confused on what I should be doing. Should I try disconnecting the battery and see if the light will go off?
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Old 03-16-2013, 10:58 AM
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First get the proper OBDII reader and read your code properly. You can then clear the code to see if it comes back. If the same code comes back then you will want to fix it or get it fixed so your car runs properly. Disconnecting the battery for 15 minutes will clear code and put your car in KAM mode as stated by 5t3alt previously. It will take approximately 20 minutes to relearn all sensors to memory matrix provided you are driving the car and not at idle. Doing this will not give you any idea on what set the code in the first place. But if it doesn't come back you're good to go!

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Old 03-16-2013, 11:22 AM Thread Starter
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Sorry i'm such a noob with cars guys! I'll try disconnecting the battery and see if comes back on after a drive.

Thank you for all your help so far, I'll keep you guys updated.
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