Here's an odd one - GM electrical gremlins

Wife's 2014 Sonic LTZ 1.4T

It's been a generally good car with a few pimples - I've put no money in it in 8 years, but it's been doing some funny things recently. I'd like to bounce this off you guys,  Nick and Pete especially.

I don't know if this is related but it may be. About 3 years ago it, twice while driving, kicked the cruise off, all the dash lights flashed and she lost most power. it eventually died and restarted. Code was P16F3 - Control Module Redundant. Shortly after I (unrelated) replaced the battery and the problem never came back. I wondered if it was possibly a short in the battery or a bad connection.

Recently two things started happening. The cruise enable won't stay on after the car is shut off, so the cruise needs to be enabled every on/off cycle now, unless it's a quick off/on. Turning the key to start the car, you have to turn it all the way til it stops and there's a fraction of a second delay before it starts turning over.

Then last week I was driving it and the check engine light comes on, but no code. I clear it, shut the car off then on restart, it's running rough, the dash is a Christmas tree, and the tach's not working, and it sets codes 262b, 0068, 0641, 0651, 697, 06a3, 2227, 0068. I think it also had code 42 at some point. I cleared everything, tried to start it again, crank and no start. I pull the cables, all the wires attached to them, all the grounds, the ECU plugs, ABS plug, I inspect (don't see anything), and I clean everything. It started up and ran fine for a few hours then I got the hard start/no tach, and codes again. I disconnect the battery, try it, and it's been running since, but the key start delay, and having to turn it to a hard stop is still there and the cruise enable still shuts off

Normally with a 10 year old car I'd start shopping and trade it in, but she loves it, it's otherwise in very good shape, like a couple year old car, and there's nothing reasonably priced right now. So I'd really like to fix it.

Ideas?

Sounds like the ecu is on its way out which is waaaaayyyyyy more common than you would think with gm cars.  I'll check the byte list tomorrow morning at work and I should be able to give you a few tests thru the fuse box for you to do with a test light......that's right......test light......per gm.  I just say that because you always hear the armchair parts changers saying you will fry everything with a test light lol.  I'll do anything to try to help keep another Sonic on the road because they are one of the most underrated cars ever.

ECU was my first thought.

When I bounced it off my buddy, who works on this kind of stuff all the time, he didn't hesitate,  smells like fuse box to me.

With older GM stuff the ecu and fuse block kinda go together.  We used to constantly replace ecu and fuse blocks together on  cadillacs of the same Era.  

The key thing makes me wonder if the ignition switch is on its way out.

Some of the symptoms sound like there is a module not getting keep alive memory power.  Because it is somewhat random, there may be a bad connection at a junction connection, or a fuzzy ground somewhere.

Replacing the battery was good.  Weak batteries can cause a lot of voltage ripple as they can not adequately damp out the AC wave from the alternator, and this can play havoc on modules.

I'll poke around iATN when I get home, but I would caution against just unplugging and reconnecting things willy nilly.  That can cause problems in itself because connectors generally are only rated for four connection cycles.  And I knew some people who would "clean connectors" by unplugging and plugging them back in ten or twelve times in a row  

Pete. (l33t FS) said:

The key thing makes me wonder if the ignition switch is on its way out.

Also came to mind.

I'm oldschool and I don't know enough about modern equipment to know what controls what, and if one connection fails how it's going to affect things down the line. As far as connections, I'm careful, I work on CNC machining centers and we have to be just as careful with drive and amplifier connectors

Thanks guys

Soooo I would try to replicate the problem by dicking with with ignition switch, then I would voltage drop everything to the ecm and look for issues there.  That being said.  Go on to ZZP's website right now and buy the big four power wire kit.  The factory power and ground wires are too thin, voltage in the car will stabilize with them.  Let me know if you want/need and schematics. 

Thanks.

I'll see if I can replicate the problem and go from there. I'll also look at that kit. I may be able to make my own

Need more information on the codes you pulled, and what modules they were in.  The prefix is important, numbers are as useless as telling someone you live at 123 without the street.

Some leads but nothing that makes sense.

gm electrical issues are just the best......and that's like all i've ever owned.

In reply to Pete. (l33t FS) :

Sweet! Thanks, I will look into it some more this evening.  In WV eating lunch at a rallycross at the moment. (Mmmm, gas station pasta salad)

Without looking into anything much, generally reference voltage issues are caused by something on that bus shorting internally and pulling the 5 volt reference down.  The key is that you look for all the items on that particular 5 volt reference line, and with a voltmeter backprobed into it, unplug those items one at a time until 5vref comes back.

I have tried to reproduce the above problems and error codes but no luck.

The cruise enable still disables on every key cycle, unless it's relatively quick.

The key switch does not require that I turn it all the way, I guess I was doing that because of the delay. As soon as you get into the spring loaded part of the switch it works normally except for the noticeable delay.

Well, it had been good for a month, but on the way home from dinner Monday I smelled something and had a look under the hood. The coolant reservoir has a small crack and was spewing coolant, likely on the fuse box, because it's been up to shenanigans again, full time now. And the fuse box I ordered is nowhere in immediate sight yet.

This thing's pulling a Volkswagen on me and driving me crazy. If I can't get parts I may just buy her another car, fix this one when I can get parts, and sell whichever one she decides she likes better.

Peabody said:

This thing's pulling a Volkswagen on me and driving me crazy. If I can't get parts I may just buy her another car, fix this one when I can get parts, and sell whichever one she decides she likes better.

you sure that's what you meant?

In reply to AngryCorvair (Forum Supporter) :

Well, she's been pissing me off lately...

Good catch, that's not at all what I meant.

Peabody said:

In reply to AngryCorvair (Forum Supporter) :

Well, she's been pissing me off lately...

Good catch, that's not at all what I meant.

I know this sentiment all too well.