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Discussion Starter · #1 ·
Ok so I bought this 2007 Chevy cobalt Lt 2.2L almost a year ago. The lady I bought it from sister got the converter replaced at a muffler shop about 3 years ago before she passed away. Then it sat in the garage for 2 years. Anyways about a month and a half ago it put out a p0420 code but had absolutely no problems. The next day it hesitated when I hit a bump,like a jerking motion. The rpms went down to like 500 and then right back to 2500 in less than a second. Now it only does that when it's above 75 degrees and it's random. It doesn't happen everytime I hit a bump. I've replaced the spark plugs,cleaned the fuel system out,and cleaned the mass air flow sensor which I'm going to replace this weekend. I was wondering if it might be the coil packs?
 

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I hope the muffler shop used a proper CAT. The factory grade CAT is very expensive and generic replacements can be had for much less. But if the CAT is not the right grade then it will not do the job. The O2 sensors will know the difference and the computer will throw that P0420 code. I don't know what is causing your intermittant hesitation problem but it is possible that when your engine stumbles it is loading up the converter with unburned fuel. That can cause the code too.
 

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Discussion Starter · #3 ·
Ok so I bought this 2007 Chevy cobalt Lt 2.2L almost a year ago. The lady I bought it from sister got the converter replaced at a muffler shop about 3 years ago before she passed away. Then it sat in the garage for 2 years. Anyways about a month and a half ago it put out a p0420 code but had absolutely no problems. The next day it hesitated when I hit a bump,like a jerking motion. The rpms went down to like 500 and then right back to 2500 in less than a second. Now it only does that when it's above 75 degrees and it's random. It doesn't happen everytime I hit a bump. I've replaced the spark plugs,cleaned the fuel system out,and cleaned the mass air flow sensor which I'm going to replace this weekend. I was wondering if it might be the coil packs?
I hope the muffler shop used a proper CAT. The factory grade CAT is very expensive and generic replacements can be had for much less. But if the CAT is not the right grade then it will not do the job. The O2 sensors will know the difference and the computer will throw that P0420 code. I don't know what is causing your intermittant hesitation problem but it is possible that when your engine stumbles it is loading up the converter with unburned fuel. That can cause the code too.
So I checked with the place that replaced it and they said they only use oem cats, but I know very little about cars so I have no idea how to check myself. I cleaned my mass air flow sensor and it has only hesitated once, I didn't know I needed to unplug the battery to reset it until last night though. So I'm gonna replace it and reset the code this weekend. I did get the fuel lines flushed out when I got my oil changed like a week and a half ago also. I'm honestly just trying to pinpoint the problem because I've gotten it looked at twice and got two completely different answers from both people and neither were helpful. The dealership told me there was nothing wrong with the cat but they wanted to replace it lol, and wanted to charge me 1k more than I paid for the car
 

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Yes, the OEM CAT is super expensive. I hope they were telling the truth but if the car passed emissions inspection then they probably used the good one. It is very hard to pinpoint an intermittent problem because you can only diagnose it when it happens. That is why the car computer will set a code and store it so you can get clues. If you do not have a scan tool now would be the time to invest in one. It sounds like an ignition problem. A loose or almost broken wire would react to a bump like that. The wiring to the coil packs is very thin and the cheap plastic protective tubing breaks easily. I would start looking at the wiring and connectors at the coils.
 

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Discussion Starter · #5 ·
Yes, the OEM CAT is super expensive. I hope they were telling the truth but if the car passed emissions inspection then they probably used the good one. It is very hard to pinpoint an intermittent problem because you can only diagnose it when it happens. That is why the car computer will set a code and store it so you can get clues. If you do not have a scan tool now would be the time to invest in one. It sounds like an ignition problem. A loose or almost broken wire would react to a bump like that. The wiring to the coil packs is very thin and the cheap plastic protective tubing breaks easily. I would start looking at the wiring and connectors at the coils.
I was actually thinking about replacing the coil packs since it seems relatively easy but I'm going to watch a few more videos on it this weekend to make sure. I didn't even think about the wiring but I will check that. If it's a wire I'll most likely have to take it in but at least I will know what it is. Thanks so much bro! Also I did get the spark plugs changed at the Chevy dealership when I got it looked at the day I was getting my oil changed, when that didn't solve the issue is when I figured out about the coil packs lol. Does it really matter where I get the coil packs from or should I go through a certain vendor?
 

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Discussion Starter · #6 ·
I was actually thinking about replacing the coil packs since it seems relatively easy but I'm going to watch a few more videos on it this weekend to make sure. I didn't even think about the wiring but I will check that. If it's a wire I'll most likely have to take it in but at least I will know what it is. Thanks so much bro! Also I did get the spark plugs changed at the Chevy dealership when I got it looked at the day I was getting my oil changed, when that didn't solve the issue is when I figured out about the coil packs lol. Does it really matter where I get the coil packs from or should I go through a certain vendor?
I'm gonna be getting a scanner tomorrow when I get paid they have them for like 40 bucks at AutoZone. Or should I get the 70$ one lol?
 

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The cheapest scanner will show codes but require you to look up what they mean. I would get one that explains the codes and shows real-time data. The better ones have a "freeze frame" feature. You drive around with it engaged, then when the problem occurs, it records the data. Then you can replay it and see exactly what was happening at the time. You say you don't know much about cars so a basic scan tool that shows codes and explains what they are will suffice.
 

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Discussion Starter · #8 ·
I'll make sure to ask them about it when I go in to AutoZone tomorrow. I'm just really hoping to pinpoint this problem a little better because I can't afford almost 3k for a cat right now especially with this one only being right at 3 years old. And sat in a garage for 2 of those years.
 

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Discussion Starter · #9 ·
The cheapest scanner will show codes but require you to look up what they mean. I would get one that explains the codes and shows real-time data. The better ones have a "freeze frame" feature. You drive around with it engaged, then when the problem occurs, it records the data. Then you can replay it and see exactly what was happening at the time. You say you don't know much about cars so a basic scan tool that shows codes and explains what they are will suffice.
So I've noticed that it does it more often if it's above 75° outside and I have my AC on, is that a sign of anything? I'm gonna be getting the scanner later on and replacing the MAF and checking the wires.
 

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I can't think of anything that would be affected by ambient temperature except maybe the coils. But at operating temps they would be getting fairly hot anyway due to where they are mounted.
 

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Discussion Starter · #11 ·
I can't think of anything that would be affected by ambient temperature except maybe the coils. But at operating temps they would be getting fairly hot anyway due to where they are mounted.
Thanks bro you've been more than helpful! I'm sure I'll be back on here some time soon again with more questions. I'd much rather try to learn to fix it myself anyways, I knew I should've taken two years of auto and not welding lol.
 

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Discussion Starter · #13 ·
I like to think I'm a pretty decent welder although I never made a career out of it lol, I got sent to prison like 4 months before I got my two year degree. I grow cannabis for a living now haha. Just happy to have found my real passion, not to mention how much money is gonna be made off of it in the next 5-20 years. Anyways I got the scanner but I haven't hooked it up yet, gonna wait till I replace the MAF tomorrow since I already have it and gonna see if it comes back on after I drive it a bit. It usually takes about 15-20 miles to come back on. Knowing my luck it's going to be cold the next 3-4 days though so I won't know if the problem is fixed until I guess either the light comes back on or when it heats back up again.
 

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Ok so I bought this 2007 Chevy cobalt Lt 2.2L almost a year ago. The lady I bought it from sister got the converter replaced at a muffler shop about 3 years ago before she passed away. Then it sat in the garage for 2 years. Anyways about a month and a half ago it put out a p0420 code but had absolutely no problems. The next day it hesitated when I hit a bump,like a jerking motion. The rpms went down to like 500 and then right back to 2500 in less than a second. Now it only does that when it's above 75 degrees and it's random. It doesn't happen everytime I hit a bump. I've replaced the spark plugs,cleaned the fuel system out,and cleaned the mass air flow sensor which I'm going to replace this weekend. I was wondering if it might be the coil packs?
Have you checked all the wires/harnesses/connectors, to make sure there seated well
 

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Discussion Starter · #15 ·
Have you checked all the wires/harnesses/connectors, to make sure there seated well
I checked the wires as good as I could, the plastic stuff around it was really fragile and just cracked when I touched it but the actual wires seemed ok. I replaced the MAF and the problem is still there but no more p0420 code, not yet at least. I'm super stumped as to what it might be. Yesterday it skipped when I hit a bump like it randomly does but this time it turned off on me and I had to pull over and crank it back up. It didn't hesitate to roll over or anything else after that.
 

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Yesterday it skipped when I hit a bump like it randomly does but this time it turned off on me and I had to pull over and crank it back up.
That would not be fuel since the injection system is under pressure. I'm thinking there is a critical wire or switch or connector that is vulnerable to bumps. Have you had the ignition key switch replaced under warranty? There was a recall. My keys fell onto the floor a couple of times and once the engine shut off. SCARRY! Once the key switch was replaced it never happened again. Otherwise something is either grounding out or disconnecting from the bumps.
 

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Discussion Starter · #17 ·
That would not be fuel since the injection system is under pressure. I'm thinking there is a critical wire or switch or connector that is vulnerable to bumps. Have you had the ignition key switch replaced under warranty? There was a recall. My keys fell onto the floor a couple of times and once the engine shut off. SCARRY! Once the key switch was replaced it never happened again. Otherwise something is either grounding out or disconnecting from the bumps.
What's the easiest way to check to see if something is grounding out other than finding the actual wire itself or is that the only way? I'm probably gonna have to get someone to figure it out but I'd like to try my hardest beforehand lol. I have not had the ignition key switch replaced yet but I did see something about that. Will the Chevy dealership just do it for free?
 

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Yes, in fact if you go on the NHTSA site Recalls | NHTSA you can search by VIN. As for finding the issue, do you have a scan tool that will do a movie? You set it up to record data and when it happens you can check to see what the actual operating conditions were. Otherwise I have to admit it will be a daunting task to track down an intermittent cut-out. It has to be something like a bare wire rubbing sharp metal. I don't envy you.
 

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Discussion Starter · #19 ·
Yes, in fact if you go on the NHTSA site Recalls | NHTSA you can search by VIN. As for finding the issue, do you have a scan tool that will do a movie? You set it up to record data and when it happens you can check to see what the actual operating conditions were. Otherwise I have to admit it will be a daunting task to track down an intermittent cut-out. It has to be something like a bare wire rubbing sharp metal. I don't envy you.
I'll definitely look into that recall. Thanks for giving me your honest opinion though man! I'll try my hardest to look over all the wires, especially the ones closest to metal lol. My buddy pointed me to a mechanic he's used in Denver for a few years so hopefully he will be able to help me out without crushing my wallet.
 

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Discussion Starter · #20 ·
Yes, in fact if you go on the NHTSA site Recalls | NHTSA you can search by VIN. As for finding the issue, do you have a scan tool that will do a movie? You set it up to record data and when it happens you can check to see what the actual operating conditions were. Otherwise I have to admit it will be a daunting task to track down an intermittent cut-out. It has to be something like a bare wire rubbing sharp metal. I don't envy you.
I only have a cheap odb2 scanner though I'm hoping the mechanic guy will have a better one
 
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