Mechanics

CHEVROLET COBALT ENGINE PROBLEM

2007 Chevrolet Cobalt • 125,064 miles

A couple years ago my check engine light turned on and I got a diagnostic test on it. The code that came up was regarding the air injection system. The check engine light came on a couple times after that and it would turn off. I went back to the dealership a couple months after to get it serviced for that and they said because my check engine light isn't on right now, to not worry about it and they cant get any information if my check engine light isn't on. My car has been running fine and the check engine light hasn't come on since.

For the past couple days, Ive been feeling my car has been working hard to get up to speed. So this afternoon I was finishing up my errands and after my last stop, I started up my car and put it in reverse and my car jerked. When I put it in drive, it jerked even harder. I accelerated slowly just to see what would happen and it continued to jerk for about a mile or so. I checked my check engine light and it wasn't even on. So I checked the coolant temp and it was running a little high (average is 189-195f and high is 200-220f). It got up to 217. The only way it gets that high I noticed is when I'm going up a steep hill. But I wasn't on or near any steep hill. So I pulled over, turned off my car for a couple minutes and turned it back on and put it back in drive without it jerking. I drove a few feet and the jerking had stopped. The temp started to go back to normal to about 185-190f.

I was wondering if there was any suggestions as to what caused this? Does this relate to the air injection system? If so how much would it cost to repair or just for parts? Could it be my transmission? Is there any kind of special service I need if its my transmission? It kinda felt like my transmission was slipping just because it had to do with my gears shifting. My cars an automatic and its front wheel drive.
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Ollebeet
February 8, 2013.



Based on your description, I would start by looking how long it has been since it had its last tune-up. We don't really use the word "tune-up" anymore, but it sounds like part of the problem is related to misfires. As a general rule when you turn the ignition switch off and restart the engine and the problem goes away, even for a little while, it is USUALLY not a mechanical problem, as in a broken part. It could be related to a worn or sloppy part that is allowing too much play, but what you described sounds more like electrical in nature.

It would take me all night to type what I know about the Check Engine light's behavior, and that wouldn't help you much. On Chrysler products once the light turns on, even if it goes back off, there will be a diagnostic fault code stored in the Engine Computer. Very often they don't get stored in GM computers until the problem acts up long enough. They call those "pending" codes, meaning the computer is keeping a closer eye on something it suspects is a developing problem. Often that problem never does develop. What is important to understand, and what your mechanic didn't describe very well, is fault codes never say to replace parts. They only tell which circuit or system needs further diagnosis. Without those codes we could spend days testing every conceivable part and still not be close to solving the problem. With the code you had before, that problem is not acting up now. That's why there is currently no code and it is why the mechanic won't know what to test or look for. He knows the circuit that had the problem, but the problem is gone now and there is no defect to be found.

When the Check Engine light stays on is when there is something for the mechanic to look for. Once the suspect part or cause is identified and fixed, he will erase the code and test-drive the car. If it really is fixed right, the code will not set again and the light will stay off. The problem is sometimes codes set after the computer runs a series of self-tests while you're driving, and certain conditions must be met for those tests to run. For that reason a problem that is still there might not be detected for many miles or even days.

Many dealerships have a sort of "flight recorder" they can plug in that you can take along for a few days. You press the "record" button when the problem occurs. Later they can play that back and look at what each sensor was reporting to get some clues. Since there's a computer memory involved, that recording actually begins a few seconds before you pressed the button, so you don't miss the event.

Also be aware there are some self-tests that some computers are programmed to do that can be felt by the driver. This is more common on cars that are only a few years old. I can't tell you what they all feel like or at what speeds they occur, but if they pass, that is recorded and often no other testing is required in states that have emissions testing.

Caradiodoc
Feb 8, 2013.


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