Chevy Cobalt Forum banner

Status
Not open for further replies.
1 - 11 of 11 Posts

·
Premium Member
Joined
·
3,860 Posts
Discussion Starter #1
Or, more importantly, what systems are affected by a check engine light? When mine comes on, like it did during the drive home last night, I can noticeably feel the lack of power, like someone flicked off the fun switch. I know the fuel trims get richer, which in turns trashes your economy, but what else is the computer trying to do to protect itself?
 

·
Registered
Joined
·
302 Posts
That's a loaded question your asking bud.

It's connected to the on board diagnostic system, without knowing exactly what code it is there is absolutely no way of knowing what the problem is. It could be a loose gas cap that will not really affect much, or a 02 sensor hurting your gas mileage or a misfire in a cylinder. The fuel and emissions systems will be affected.

Without scanning the car to figure out what code it is, there is nothing you can do that will be productive.
 

·
Super Moderator
Joined
·
11,821 Posts
If I understand your question correctly what you want to know is what does the "ECM" do when it detect a "DTC". Well if it is related to "MAF" "HO²s" "IAT"or "MAP" the "ECM" will go into open loop therefore falling onto a predetermined set of parameters like when you start your car. Which is what happened in your case.

DTC P0171
Circuit Description
The engine control module (ECM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy, and emission control. Fuel delivery is controlled differently during Open Loop and Closed Loop (CL). During Open Loop, the ECM determines fuel delivery based on sensor signals, without heated oxygen sensor (HO2S) input. During CL, the ECM adds HO2S inputs to calculate the short and long term fuel trim (FT) adjustments. If the HO2S indicates a lean condition, the fuel trim values will be above 0 percent. If the HO2S indicates a rich condition, the FT values will be below 0 percent. The short term FT values change rapidly in response to the HO2S voltage signals. The long term FT makes coarse adjustments in order to maintain an air/fuel ratio of 14.7:1. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term FT diagnostic is based on an average of cells currently being used. The ECM selects the cells based on the engine speed and load. If the ECM detects an excessively lean condition, DTC P0171 sets.

If this code was set because you drove through higher elevations it will reset after 3 startups.
 

·
Premium Member
Joined
·
3,860 Posts
Discussion Starter #5
I understand how the ECM defaults to its 'cold start-up' parameters when it springs a code, in an effort to protect itself from possible damage. My code came up a month after I installed my CAI, it lasts for a few drive cycles, clears itself and is dormant for a week or two. Then it pops up again, usually after a case of lead foot, only to disappear again. My MAF is as clean as a surgical tool and I've tightened and readjusted the intake tubing to insure there are no leaks before the TB. Other than that, I was suggested to replace the O2 sensors as they are a bit of an achilles heel. Anyways, my original question, however poorly worded, wanted to know how much power the engine is putting out in open loop mode.
 

·
Super Moderator
Joined
·
11,821 Posts
It will be different for every car because nobody knows on which side of the power curve your car runs at in closed loop. Most cars run richer and have more power at certain "RPMs" and less at others. GM can't afford to waste time to tune each car on the assembly line so the preset values are middle of the road for most.
 

·
Super Moderator
Joined
·
11,821 Posts
I'm saying 2 exact same cars off the assembly line can perform totally differently. One can be a 50mpg car and the other a 30mpg car but on average they will get 40mpg. There are 60mpg XFE and some can't touch the 40mark.
 

·
Premium Member
Joined
·
3,860 Posts
Discussion Starter #9
I was hoping you'd say something like Herbie from The Love Bug exists out there, fully aware and humanlike capable of feeling pain and emotion, fiercly loyal and fast as hell. I may be delusional, but I think my car has a bit of that spark within her... Call me a dreamer, I got that disease.
 

·
Premium Member
Joined
·
2,068 Posts
Haha I feel the same way. I feel like my car is pretty quick, but of course the racing stripes on the hood add 70 HP.

2005 cobalt base model coupe
 
1 - 11 of 11 Posts
Status
Not open for further replies.
Top