Chevy Cobalt Forum banner

Status
Not open for further replies.
1 - 20 of 28 Posts

·
Registered
Joined
·
10 Posts
Discussion Starter #1
Hello all. Hope you may offer some advice and help cure a problem my vehicle has developed. 2008 2.2 ltr LS. Was taking my son cross country, San Diego to Michigan. Half way through our trip the car developed what felt like a miss. After a few minutes I lost the accelerator. At this point I pulled over and let the car idel for a few minutes and the accelerator began to work once again. As we continued, the miss would come and go. At one point I thought the vehicle was going to stall so I shifted from 5th to 4th and punched the accelerator. Oddly enough the miss went away, but at the same time my tach fell to 0. Long story short, we took the car to the shop and was told the crank sensor was bad. Replace it and two weeks later the problem has returnred. Every time this miss occurs, the tach will fall off and engine runs fine. Problem will return once the engine is turned off and restarted. I am now receiving a code that states bad crank sensor. Any Ideas? Took the car back to the dealer but they could duplicate the problem.
 

·
Super Moderator
Joined
·
11,821 Posts
Don't know why (yet) your "ECM" would give you a faulty crank position sensor, because what you are describing is a faulty cylinder #① ignition coil. Tach gets it's information from ignition coil one, if it fails you lose your tach, if you lose your tach you lose rpm information to "ECM" it then falls into limp mode or engine management mode if you prefer that term. The only thing that bugs me is why didn't you get a P0301 code.....and why a P038*
 

·
Registered
Joined
·
10 Posts
Discussion Starter #3
I can recheck the fault code and repost, but would a faulty coil pack be that intermittent? All seems to reset once the engine is turned off.
 

·
Super Moderator
Joined
·
11,821 Posts
Yes, because it cools. They are all the same so just move two around and see if the symptoms change.
 

·
Chevy Customer Service
Joined
·
794 Posts
Good morning Taylord,

I see that you've visited the dealership and they were not able to duplicate the problem, and it looks like Coby7 is on the case as well. If you had wanted for me to follow up on your visit with the dealership, please let me know! I will provide you with my email address (as you're newer to the forum, I don't believe you can private message yet) and we'll go from there.

Sarah, GM Customer Service
 

·
Registered
Joined
·
10 Posts
Discussion Starter #6
Rechecked the codes, I have a P 0336, and P 0507. As of now the vehicle is in the shop. They stated it may be a few days, so I will post again when they give me their assessment.

Thanks for the input.
 

·
Chevy Customer Service
Joined
·
794 Posts
Hi Taylord,
Thanks for the update! We hope you're on your way to finding the source of the misfire. Just checking - is your shop one of our dealerships? I want to make sure to be available to you if you should need any assistance.

Sarah, GM Customer Service
 

·
Super Moderator
Joined
·
11,821 Posts
I doubt that even the first sensor was bad, they will probably find a chafed,burnt or frayed wire. DTCs are a guide to trouble shoot not an absolute.

DTC P0336
Circuit Description
The crankshaft position (CKP) sensor is a variable reluctance sensor. The CKP sensor indicates the crankshaft speed and position. The CKP sensor produces an AC voltage of different amplitude and frequency. The frequency depends on the velocity of the crankshaft. The AC voltage output depends on the crankshaft position and the battery voltage. The CKP sensor works in conjunction with a 58X reluctor wheel attached to the crankshaft. The CKP sensor is also used to detect misfire and tachometer display. The CKP sensor connects to the powertrain control module (PCM) through the following circuits:

• The CKP sensor signal circuit

• The low reference circuit

If the PCM detects an excessive number of resyncs from the CKP sensor, DTC P0336 sets.

---------- Post added at 02:01 PM ---------- Previous post was at 02:00 PM ----------
So you can probably disregard this DTC
DTC P0507
Circuit Description
The throttle actuator control (TAC) motor is controlled by the powertrain control module (PCM). The DC motor located in the throttle body drives the throttle plate. In order to decrease idle speed, the PCM commands the throttle closed reducing air flow into the engine and the idle speed decreases. In order to increase idle speed, the PCM commands the throttle plate open allowing more air to pass the throttle plate. If the actual idle RPM does not match the desired idle RPM within a calibrated time, this DTC sets.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #9
OK, just got off the phone with the local dealer, and the service department claims my problem is a binding throttle body. Repair for this is in excess of $650. Need some input here, as this is the third time to the dealers and it seems like every time I take this vehicle in the problem diagnosed keeps changing. Furthermore, the dealer now wants $100. just for tlooking at the car. As a note, this car is not under warranty. Is there a way to test the throttlr body myself, and does anyone have any other thoughts as to my problem given the codes listed. I know I have a small vacuum leak, but this problem occured after the fact and is something I can easily fix myself.
 

·
Registered
Joined
·
5,481 Posts
Buy a used TB for less than $100 and replace it yourself. It's only four bolts! If that even is the problem.
 

·
Registered
Joined
·
5,481 Posts
Take off your TB and make sure it's not all gunked up with carbon first.
 

·
Registered
Joined
·
5,481 Posts
If you can move the valve easily (not all the way open, do not put extra pressure to open it!!!) it's as good as new. There might be a problem with the electronics inside, but I would doubt that.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #15
So with the car off I should be able to open and close the valve? I take it I do this with the battery disconnected as well?
 

·
Registered
Joined
·
5,481 Posts
Perferably you should take the entire TB off the car to clean both sides of the valve. You can try moving it then.

It's litterally four bolts holding it onto the manifold.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #18
Ok,got it back fro the dealers, same problem. Throttle body checks good, cleared the codes and took her for a run. Same issue. Runs fine for a while then bucks three or for times the tach falls to 0 then engine runs fine. So far I have checked all wires vacuum lines switched crank sensor, moved and checked coil packs, cleaned throttle body and changed plugs. I am at a loss. Still idles a bit high as well. Any other thoughts out there?
 

·
Super Moderator
Joined
·
11,821 Posts
If you already paid to get it fixed and the issue wasn't resolved bring it back. Sarah here should help you with any dealer issues. You should not have to pay a second time for the same problem.
 

·
Registered
Joined
·
10 Posts
Discussion Starter #20
No, would not let them work on the vehicle, they are telling me that it is something different now so I think I will do some more trouble shooting on my own.
 
1 - 20 of 28 Posts
Status
Not open for further replies.
Top