Intermittent Stalling & Almost-Stalling With No DTC = Fuel Delivery System Problem?? - Chevy Cobalt Forum / Cobalt Reviews / Cobalt SS / Cobalt Parts
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post #1 of 4 (permalink) Old 06-11-2019, 12:31 PM Thread Starter
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Intermittent Stalling & Almost-Stalling With No DTC = Fuel Delivery System Problem??

Original owner of a 2005 Cobalt LS with an engine issue that's difficult to replicate and diagnose.

Everything generally runs fine, no leaks, performs well, always starts up smoothly, all mechanically good, maintained throughout its life primarily at the servicing GM dealer. Never been in a collision, flood, modified, etc. Kept very clean.
A few months ago, the car began exhibiting intermittent stalling and nearly-stalling incidents where it seems to "recover" itself quickly enough to continue running. Never struggles, just dies. Doesn't matter whether you're idling or cruising, highway or city driving. The problem is, there's no DTC generated, not even anything pending according to my Autel AL319 reader. Curiously, the runtime since engine start parameter resets whenever I experience one of the almost-stall events, even though the engine doesn't fully quit running.
These hiccups occur maybe once every few times the car is driven, without any common conditions. The check engine light comes on as soon as it begins to stall, but goes off within one second, usually when the engine RPMs go back up to normal. It happens so fast that unless you're staring at the dash, or accelerating hard and feel the brief loss of power, it's barely noticed. If the engine does completely quit, it's immediate, as if the ignition had been abruptly shut off, and I can always restart it without difficulty, suggesting it's not misfiring. Ignition switch never comes out of the run position on its own.

First attempted remedy, I had the throttle body cleaned, but the problem persisted. Then, I checked the fuse boxes and everything seemed snug, no sign of contamination or anything blown/burnt. Had suspiciously similar ignition module problems with a different (Ford) car I used to drive, so I tried replacing the ICM, but that didn't fix it, either.

Sure, something common like a corroded ground connection is possible (often a nightmare to locate) but I'm beginning to wonder if it's rooted in an electrical or fuel delivery fault. Should I try getting the fuel injection serviced? If the injectors are dirty and/or the fuel filter is slightly clogged, could these conditions cause random engine shutdowns without any codes, yet otherwise operate perfectly normal?

The odometer just hit 78000km (say, 48000 miles) so yes, it has very low mileage; gets used once or twice a week, lately... formerly used the vehicle to commute to work during its first six years or so.
I have online access to the chiltonlibrary.com database (mostly a replica of GMSi) and have not found any applicable tech bulletins.
Eight years ago, I had the TCM replaced at the stealership after the car suddenly acted like it was electrically possessed while running, but I've read numerous accounts that apparently it's a common problem.

Seeking help/suggestions from the audience...
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post #2 of 4 (permalink) Old 06-11-2019, 12:39 PM
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I'm just going to say this as odd as it sounds to you, but I want you to please consider it seriously as it sounds like the start of my previous issue. Get the battery checked out. If it's on the low side, get a new one.

I started getting those issues, and it turned to crazy relays and other things with no DTC. Someone from one of the Cobalt forums recommend I checked out the battery, and I was actually on my way to do it when it quit hard and wouldn't turn over again. Had to have it towed. Took my summer driver and got the battery replaced, no problems. The guy that tested the battery said the battery checked good, even though it was on the lower side.

I remember the user on the forum said anything on or lower than 11.86V is pretty much going to cause issues.

Good luck!

-Sam

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post #3 of 4 (permalink) Old 08-04-2019, 11:30 AM
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I worked on a 2005 cobalt with the same symptoms. I fixed it by cleaning the throttle body. It was badly caked in carbon and it idled smoothly and no more near stalling after that.
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post #4 of 4 (permalink) Old 08-18-2019, 01:38 PM Thread Starter
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solved: bad engine control module

Well, in the end, it was a faulty ECM. Ordered an OEM replacement from a parts business in Michigan that had lots of 'em at a great price, then had the dealer program the VIN, and do the crankshaft variation + theft deterrent learn.

Replacing the battery was a good advice because I forgot mine was now eight years old, but that didn't fix the problem.
Unfortunately, I had to shoot a bit of a parts cannon at the car before isolating the intermittency to the ECM. Tried replacing the fuel filter, then the crankshaft position sensor; neither had any effect. Had all electrical grounds tested; they were fine.

Anyway, who manufactures GM's automotive computer components? In the life of my babied Cobalt, I've had to replace the TCM and now the ECM. Not impressed at their durability, and these things are ridiculously expensive. I would have expected fluid leaks and other mechanical fatiguing by now, not sealed electronic module failures. Then again, it seems like a bad idea to design vehicles with these computer modules inside the volatile engine compartment. Someday I'll get myself a pentalobe screwdriver bit so I can take apart my old ECM and investigate how well it was made.
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