Hi guys,

Over the past few weeks, I've noticed my 2006 Cobalt SS/SC has been running funny. It's been getting progressively worse. Yesterday, it got to the point to where it would rough idle when sitting still, especially if I had the AC on, as well as stall when I tried to accelerate. It didn't do it so much in first gear, but anything about that was terrible. The RPMs would slowly go up, but the supercharger PSI shot up to 15 every time I even tapped the gas pedal. I thought it might be the throttle body, so I went ahead and cleaned it. The CEL was on before I cleaned the throttle body, but it always stays on, reading system too lean, due to an aftermarket air intake, so I didn't even check it. Well, after cleaning the throttle body, and it didn't help the condition, I decided to check the code. It was reading P0128, which is an Engine Coolant Temperature code. This morning, I went out to head to class. After starting my car, the RPMs were all over the place; jumping to 2,500 then dropping to 500. It was kind of cool this morning, as well. I let it sit for a few minutes, then got on the road. After around 3 minutes, I got the "ENG PWR REDUCED" message and the car wouldn't go above around 5mph. I let it sit for a few minutes, then was able to make it to class. The car was still running rough, though.

Does anyone know what could cause this? I've read the P0128 could be a bad thermostat. I'm not sure if that would cause all of these problems, though. I've searched the forums, but couldn't find this exact problem. Thanks for any help offered!

 

Engine Power Reduce Mode will not limit your speed. It opens the bypass valve and does not let you build boost. It also prevents the car from going into the PE table. Basically, it is GM's way of having people bring them the car.
I comes on from a few things: air flow, spark, or fuel. Usually the most common cause is the throttle body, did you make sure the wires clean and the connector is not corroded?

Also, the fact that a small rev shoots boost to 15psi when it is not in EPR mode tell me that your cat is clogged. This would prevent exhaust from leaving, choke up the motor, cause a lean code, and force the car into EPR mode.

Unbolt the downpipe and see if the issue clears up.

What are your coolant temps?

 

Coolant temps, based on the DIC, usually stay around 180-189. This morning, it didn't get above 150. And thanks, I'll try that about the downpipe. Is there a tutorial anywhere on how to do it? I don't know much about cars, I just find all the information on this site through Google lol.

 

It is three 13 or 15 mm bolts where the header meets the downpipe. Then two on the exhaust side. Unclip the sensor and pull the pipe out.
It will be loud as ****, but go for a drive and see if the issues clear up. Look inside the DP and see if the cat is gunked up. Shake it. If it makes noise or is visually clogged it is done.

How long did you let it warm up?

 

That doesn't seem so bad. I'll start working on it when I get home in around two hours. I let it warm up for around 2-5 minutes. I believe it was around 50 when I started the car, and around 120-130 when I started driving.

 

It takes a lot longer then a few minutes to warm up an LSJ

 

Ah, didn't know that. Good to know for future reference.

I checked the cat and it seems fine. I decided to clean the MAF and SCIP sensors, but it didn't help at all. I've been reading codes all day and clearing them every time I do a reading. Below are all the codes the car has given throughout the day (besides the P0128 code mentioned earlier).

P0068 - Throttle Body Airflow Performance ECM, PCM
P1182 - Supercharger Inlet Pressure Sensor Performance PCM
P0102 - Mass Air Flow (MAF) Sensor Circuit Low Frequency PCM
P0507 - Idle Speed High PCM

The P0102 and P0507 have only appeared once. The P0068 and P1182 come back as soon as I turn the car off and then back on. My uncle told me to do a test on the MAF after the P0102 message appeared. I started the car and then unplugged the MAF. He said if the idle got worse, the MAF is good. If it stayed the same, it's bad. The idle definitely got a lot worse once I unplugged it. After reading the codes, and forums, it seems like the next culprits are the SCIP sensor or the bypass valve solenoid (based on suggestions by other members).

Does anyone know which would be more likely? I'm on a very tight budget at the moment and would like to get it right the first time, although I know that's difficult to do with issues such as this.

 

A new MAF is $45 on amazon.com and it is OEM and brand new. Buy one.
Unplugging the MAF isn't the same on these cars because speed density. When the MAF fails it picks up and runs on the MAP.

Replace the supercharger boost sensor and go from there. Sounds like you need the SCIP and MAF though.

 

I had something similar happen to me once. I cleaned the TB, replaced the SCIP, and replaced the TB. That is what fixed it for me. I think old TB was still not 100%.

 

Anyone know the part number for the SCIP? I need to replace mine too.

 

Pretty sure it is this one.
The 3-wire sensor on the blower.
GM 12614973

 

Okay, seems like every part on my car is messing up. The day after my last reply, the car just shut completely down and hasn't started back. When I try to turn it on, the engine tries to start, but never does. I've replaced the SCIP, MAF, and throttle body. Replacing those may have helped my previous issues, but the car won't start for me to check that. I noticed I could smell gas when I replaced the throttle body, which I found odd since I haven't tried to start the car in several days. When I got the new throttle body on, the car started, but shut back down. It led me to question if this is a fuel problem, so I forced fuel by turning the ignition switch on and off. Sure enough, after a few times, the car started, but shut down immediately. Now I have a CEL P0230 code. What's the best place to start for a code like this? So far, I've tried the following.

Tested the fuel pump relay
Tested the fuel pump fuse

Would the next step be to replace the fuel filter? I'm guessing it could also be something electrical, based on what I've been reading about the issue.

 

Can you hear the fuel pump prime?

in dead silence turn the key to on and focus hard listening neat the back seat. If you cant hear it whine as it primes, it is dead.

 

Thanks, I'll try that. It's gonna suck if it's a dead fuel pump, considering I had it replace around a year ago.

 

You can also rent a fuel pressure tester for free from autozone. Their kit has the fitting that fits the LSJ; I used it on mine when I was having fuel starvation issues. My filter ended up being clogged and my rail pressure was low.

 

I gave it a listen test and the fuel pump is priming. I also ran a pressure test and the rail pressure is good. I have no idea what to try next. I called a dealership and asked them about it, since I can't drive it in, and they want me to get it there so they can reflash the computer. They say that will fix the problem. Considering the haven't even seen the car in person, I'm not sure I believe them on that.

Not sure if these videos will be of any use, but here's what the car is doing.

 

Did this issue ever get resolved? Im having a similar problem with my car right now.