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Discussion Starter #1
Hi everyone,

I'm new here, but will most likely be hanging around as I am planning to keep this car until the wheels fall off...

I have a 2006 Cobalt with a 2.2L and 5 speed that has been giving me a heck of a headache lately. My ex and I bought this car brand new at the dealership I had been working for at the time, (Kelle Chevrolet) and she used it as her daily driver for almost 10 years, putting 101k miles on the odometer.

Never gave us much trouble during those years. It had a miss at around 60k a couple of years ago and I had to replace the coil pack to fix that.

At around 98k, she was driving to work and it BROKE the timing chain tensioner, skipped a few teeth and bent all 8 intake valves.. So, I pulled the head, replaced the valves, timing set, cleaned all of the pieces out of the pan and it was back on the road for another 2,000 miles, until... morning, it began running rough and was throwing all kinds of random codes, and after messing around with it for a bit, I found the underhood Fuse/Relay box was all corroded around the area where the PCM relay would sit. I took the box apart and it was so nasty, that the corrosion had caused circuits to "cross" on the board and it was burned up in several spots.

I replaced the Board and the car was fine again for 1,000 miles or so until it started running crappy again and stalling.

Unfortunately, around this time, our relationship pretty much 'hit the fan' and she ended up trading the car in for a New one without my knowledge.

Anyway, long story short, I ended up finding out and bought the car back for myself as a non-running vehicle because I really loved the car and brought it home. My daughter and I spent the weekends over this past summer cleaning the car all up (my ex wasn't the "neatest" person I've met, for sure), we replaced the carpet and thx to a wrecked donor car, we changed the interior over from a coffee stained, beat-up and filthy gray, to black and installed a killer stereo setup too...

OK, HERE'S What I've noticed with the car:

- My MODIS IS able to identify the vehicle
- Data Stream shows ECT to be -40 F (Cluster does too)
- RPM displayed is correct
- TAC or engine load is at around 60% just trying to keep itself running
- Many random codes come back after clearing and restarting
- Showing NO misfires with data stream (??! sounds like a T/F dragster at idle)
- Cluster Displays 'Engine Power Reduced'
- The vehicle has also 'Disabled Engine' 2 times on me in about 30mins of total run time


- Cleaned Throttle Body
- Cleaned Connections at ECM, Relay/Fuse box
- Cleaned MAF
- Replaced Ground Strap from Head to Valve Cover
- Replaced Ground cable from Block to Chassis
- New Plugs
- New Fuel in Tank
- Compression test
- Smoke tested Intake and Vac lines
- New ECT sensor

I don't remember all of the DTC's but can go pull them if it might help (In honesty, I didn't see anything that really "jumped out" at me to lead me in any direction... In other words, it runs so crappy that it seems to log all kinds of different random codes each time I clear them and run it again)

Thanks very much in advance for ANY ideas! I hate chasing gremlins in Freezing cold driveway!!

Also, if anyone knows where I can get a Good Wiring diagram(s) (even if it costs me a few bucks), I would REALLY LOVE to have that!!

---------- Post added at 09:50 AM ---------- Previous post was at 08:19 AM ----------

Oh, also forgot to add, The cooling fan seems to run at random with the engine cold

Super Moderator
11,821 Posts
Cooling fans will run if you have front windshield defogger ''ON''

You seem to be describing a plugged CAT. Take the first HO² out and insert a camera in the exhaust heading towards the CAT if the honeycomb has collapsed or has melted shut, that will be your problem.

491 Posts
Coby7 has just about every schematic for the 06 Cobalt posted in the 11,000 posts he has here on the forum.
Between here and Autozone dot com you will have what you need as far as wireing diagrams.
Note, these cobalts are known for corrosion related electrical gremlins and since the engine is a "run by wire"', a good electrical system is a must. Down this line, you will want to know the ground locations. There are posts here showing most all of the ground points" ". You may also wish to deep deep clean your BCM and ECM.
Coby7 has a "how i did it" BCM repair you might find useful and can post a link to it.
One reoccurring recommendation is to clean the contacts of the BCM by multiple disconnect and re-connect cycles followed with a generous application of dielectric grease. (Loss of gm lan)
Good luck on isolating the errors and learning how to search the forum.
Use the advance search, enter diagram for subject and Coby7 for user name then check show results as posts
And enjoy.
Share your ODB codes and you'll get a quicker pinpoint diagnostic.

4 Posts
Discussion Starter #4
Firstly, THANKS for the replies and ideas.

Coby7, it did act very much like a melted cat. I pulled the pre-cat O2 to see if it would rev up or run better, but, it was still the same... (actually, the way it was dumping fuel, it probably eventually would have ruined it!)

So.. I had some time on Thursday to go to the garage and mess with the car some more... It's actually pretty humorous what the problem(s) were with it, IMHO...

Turns out, the Ford stealership that she traded the car in at, had some "hammer head" trying to fix the car for re-sale...

When I got the thing back to my place, it was kinda half-arsed thrown back together, and to make a long story short... They had the speed sensor connector plugged into the Coolant Temp Sensor, and then the connector for the temp sensor was plugged (well, more like jammed) into the evap Purge Solenoid. Then, they had taped up the evap Purge connector and tucked it into the harness (must've figured it was an "extra" connector for something the car didn't have, since there was no place left for it to plug into)...

I came to realize the problem when I saw the 'buried way down low' VSS had nothing plugged into it.

I overlooked that, I suppose, mainly because they told me they "never touched the car", and I was the only person who worked on the car since it was new. Also, they had half of the harness routed around the wrong side of the radiator hose, so the connectors couldn't even reach to where they were supposed to go.

The PCM was doing all sorts of weird things. So, between that going on, me believing the car was 'un-molested' and not being under the hood of the thing for a while, it really started to send me on a wild goose chase...

So.. after fixing the harness issue, I had a normal coolant temp reading again, but the car continued to run like crap, and in reduced power mode, still.

I looked at data stream again with the car running, and saw the throttle was opened about 60%, no matter where the accelerator pedal was, and injector pulse width was like over 10 m/s at idle, and it pulling a ton of timing back (I imagine to keep itself from revving to the moon). The throttle body became my most likely suspect, and with "me, being me", I tore the side cover off of that puppy to do some interrogation...

Sure enough, the thing was opened about half way with the car running. I grabbed the 'sweeper' for the TPS and forced the throttle shut, and she started idling beautiful, like a brandy-new ecotec.

But, now I wondered why doesn't the PCM just close the darn thing on its own? I swept both the gas pedal TPS and the T.B. TPS (several times) and neither one had a glitch or any opens or shorts.

I took the Throttle Body off of the car, put it under a good light, and started poking around...and... Wow!! The stepper motor had a near invisible crack between one of the two tabs where it connects to the circuit board.

I applied a dab of solder into the crack, put it back together, and she runs like a champ!

That was a pretty crazy ordeal!

And again, THANK YOU guys for the replies, and ideas. VERY much appreciated!!!

PS- If anyone is curious about other details from this little adventure, I'd love to share
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