First, my apologies if this has been covered else where but I have been unable to find an answer or get a resolution for this problem.

About 2 months ago the CEL came on. The car had about 75k on it with no issues at all. I took it to a local mom and pop shop ( trying to help the little guys out) who read codes for a bad O2 Sensor. Both O2 sensors were replaced and all seemed well for a few days. CEL came back on, same mom and pop now says there are multiple codes, and some conflict with each other. Reset of ECM did not resolve the issue as codes came right back. Shop called local Chevy dealer who stated it sounded like a bad ECM. it was ordered and arrived 3 weeks later ( I was none to happy as they never bothered to tell us it was back ordered) ECM was replaced and programmed by the dealer. The original shop has been playing go between as he was frustrated as well and wanted to see this through. Dealer stated they did find the original ECM faulty. They also had difficulty programming the new one. I picked it up that evening, started it and Voila, CEL is back on. Codes are in excess of 45 most conflicting with one another, claiming misfirings, traction control malfunction ( vehicle never moved) etc. Dealer was called and claimed the new ECM was still "learning" the car advised to clear the codes and it shouldl be fine. I drove the car 400+ miles over the next 5 days with no issues then on a cold start CEL came back on. I should also say the CEL only came on when it was a cold start. Never while the engine had been running for a time or on a warm resart. Dealer told the Shop to check for a bad ground. No bad grounds were found but dealer also did ask the shop to systematically add new grounds. 6 have been installed in all 4 in engine compartment 2 in trunk to battery. Still no resolve. in fact the diagnostic machine claims multiple fail codes again. So many, the dealership has no idea how the car is even running.
This car runs like a top, never misfires, the only thing comprised is my MPG as it went from low 30's to low 20's since this has happened. Dealership is supposedly trying to get an answer from Mother as to what this could be but have not come up with anything definative. I licve in CT which requires Emmision testing and lucky me my is due at the end of the February. It is am automatic fail if The CEL does not clear and or the fail codes. Needless to say I'm more then annoyed, I have a semi perfectly running vehicle with a new ECM and and extra 20 feet of ground wire that wont pass emissions. A little help please? Pretty please? LOL

 

Instead of having someone say its this or that. best thing to do is they need to diagnose. Like check resistance from begining of o2 wire to ecm. Then check grounds and ect. I amcan almost tell you Ure issue is either 02, a fuse or wiring

 

Understood, and if I'm not mistaken A resistance check was done by both the mom and pop and the dealer. This is becoming frustrating but I appreciate you taking the time to look at this.

 

If they took the time to check the ohms and they suspected ecm because wiring tested good. And it still throws codes. Replace o2 with a acdelco product not a Bosch. They are universal and junk. Also if you have a header or any type of exaust system itll cause issues.depending on codes

 

SteveV1231,

If I can be of any assistance by calling to follow up with the dealership on this, please let me know more information in a private message (include your name & contact information, the last 8 of your VIN, and the name of the dealership).

Best,
Sarah
GM Customer Service

 

I honestly don't remember what brand o2 sensors of we replaced them with already. I will check though. As far as the rest of your statement if I understand it correctly, the vehicle is completely stock nothing has been modified. as far as the codes go, its just about everything from o2 sensors to crank sensors to cam sensors to faulty idle sensors to knock sensors to faulty gas gauge sensor to tank sensory to major vac leak to m minor vac leak (gas cap has been changed out) ..you get my drift, its EVERYTHING LOL I watch to punch some thing .


Thanks Sarah, I get that back to you in a private message

 

To me that seems like it would be a grouse or even the fuse box relays or fuses

 

there is so many ground wires in the vehicle now, its like driving a Tesla Coil :-) The ground to the battery was really flimsy from what I saw. That one has be anchored nicely along with the other 5 lengths of number 8 wire. though out the engine compartment and trunk. I will check the fuses myself any fuses I should be looking at in particular? Everything seems to be working as it should, well for the exception of the CEL LOL

 

Yes all fuses and including the box itself .. remove the entire box and inspect it

 

ok, lovely LOL

 

Just a thought, my car started throwing a bunch of codes one time that I knew where impossible for all those to show up at the same time. Never the less I replaced a couple sensors based off of the CEL codes. Even after replacing said sensors, codes were still on. I found that I had 2 vacuum (one minor & one pretty bad one) leaks under the hood, fixed those and codes went away. Not sure if this might be your problem as so many mechanics have looked over it, I would hope they'd have noticed that. However, cant hurt to check.

 

Thanks Nizzle, I left out they smoked tested the system when the gas cap was replaced LMAO So much has been done I forget. It is definitely worth revisiting thought.

I have to tell you all thanks a bunch for your responses. Its got my gears turning. Hopefully some thing that comes across here will click. Keep'um coming. :-)

 

damn bro! Good luck

 

There is such thing as TOO Many grounds... Each ground wire has a little bit of resistance, and a diffrent ammount of current in it, wich will cause the end that doesnt go to ground to be at a slightly diffrent poltential.

The best ground is everything going to ONE ground. If you get too many grounds you can get erronious signals on gruond currents and everything.

When I instaleld my Interceptors, Analogic, Sensors, I wired everything to ONE grounding point.

 

Hi Jonathon,

Thanks for the advice and suggestion, this will be delved into again. The grounds were added by the mom and pop shop at the direction of the dealership, after the 2nd ECM was installed and it began throwing the hodge podge of codes again. so although it is probably an issue it wasn't the root cause. I'm not a mechanic, and my knowledge of engine operation is very basic, so every little bit helps. If my car was a person and having a heart attack I would be more comfortable with diagnosis and treatment LOL

 

They make kits like a Grounding kit. Where the idea is that everything has/shares the same ground, thust at the same ground poltential... One of those MIGHT help some.... But really your basic, BEST ground is going to be the Engine Block. The cross sectional area of the block is Ginormous to give you good connection to the alternator, where when the engine is running is the power source.

Another thing to check is see if there is an electrical connection between the engine block and your frame. Alot of things use the frame as a ground and then have a bonding strap to allow the electrical current to pass from one to the other. If the bonding strap is come loose, or deteriorated, it could cause a differeance in electrical poltential and cause some of the systems in the car to see the wrong voltage/signals then others. If that is the problem just run a wire from the block to the frame, Make sure its a heavy gauge wire. The higher the cross sectional area of the wire, the less the resistance and the lower the electrical poltentional accross it.

A Good check of this get your car running, and measure the electrical voltage between the engine block and the frame of the car. You might have to set the volt meter to milivolts though.