Yall, I had a p0420 and was just riding on it because I didn't want to replace the CAT. I started having issues posted in bulletin 14311 (negative battery terminal cable 10yr/120k mile bulletin about the crimp not being enough on the connection to the stud on the body), and I know the negative battery cable has never been changed so I changed it with a OEM part, there is also a bolt you're supposed to use to replace an existing stud on the terminal for the new cable and a bigger nut to go on the ground to the body. Its all detailed in TSB 14311, the parts counter at any GM dealership can give this to you even if they say they can't. I decided I would clean the positive battery cables too just to be thorough. The 250 amp fuse to the fuse box on the fuse bus broke completely off without effort. I looked up parts online, nowhere to be found. You can get it cheap on amazon but the quality is not the same as OEM, sorry its just not. Bought a new fuse bus and greased all connections, cranked the car and the code immediately disappeared.
The ambient temperature sensor did not come on and the drivers side window didn't want to do auto up, but turning the car off and cranking it again solved this issue. I let it idle to warm and sat watching the voltage on the cluster. It never moved from 14.7v, which is a new thing for me. It used to always fluctuate from 12-15.5v. Even drove it 5 miles, the 14.7v never changed. Car had much better response. I thought it was just an old car and it was normal to be a little sluggish. Nope.

I'll post an update if the code comes back.

TSB: https://static.nhtsa.gov/odi/tsbs/2015/SB-10057574-6264.pdf

Parts List:
22754271 -> Cable Assembly
11561025 -> Bolt
96889385 -> Fuse Block Assembly (I recommend getting from a dealership, amazon has it for less but the terminal cable looked different than OEM. Also could not find consistent pictures of the fuse bus 100a 100a 80a 80a)
Electric Grease
Battery Terminal Protectant Kit

I greased the connections for all the fuses. See the attached image. Dont worry about putting them in the wrong place. They're numbered on the metal.

I'm all for saving money, but the Cruze is a high voltage, sensitive system which is why I'm stressing OEM.

Welcome Aboard!


Service Bulletin - NHTSA SB-10057574-8899
SB-10089945-2280
How-To: Installation of the Big 3 Cruze Kit
Clean the Terminals
Cruze Battery Upgrade Options

 

Change the battery and your voltage will fluctuate again.

I had the same problem 3 months into newly purchased. Battery got warranteed.

 

let it idle to warm and sat watching the voltage on the cluster. It never moved from 14.7v, which is a new thing for me.

I wouldn't confuse this steady voltage with your fix. After having the battery disconnect the car assumes it is only 20% charged, and bumps up the voltage according. Very few people know the alternator is controlled by a very complex algorithm and sensors. A varying voltage is mostly a sign of a healthy charging system.

Thx for posting this, I literally tell people here constantly how important a good electrical system is to our cars. And I'm usually meet with argument and disbelief.

 

I wouldn't confuse this steady voltage with your fix. After having the battery disconnect the car assumes it is only 20% charged, and bumps up the voltage according. Very few people know the alternator is controlled by a very complex algorithm and sensors. A varying voltage is mostly a sign of a healthy charging system.

Thx for posting this, I literally tell people here constantly how important a good electrical system is to our cars. And I'm usually meet with argument and disbelief.

I had gone to advance auto and was told the battery was at 75% so it makes sense that the 14.7v was to charged it up. After 1 day of driving the voltage is fluctuating between 14.2-14.6 but the interval is significantly decreased.

 

I know the car is a 2012, but the fuse bus breaking was pretty wild for me. I guess the resistance from the battery cable never being replaced weakened it? I have no idea. I love GM for the most part but their maintenance schedules and TSBs are minimal at times and don’t address the consequences of some issues

 

Code is back, I’ve read other threads and found that the alternator can over charge causing the ecm to short. So if I just completed tsb 14311 after having the car almost 10 years then the damage is probably done if its that. I’m going to check the connections to the intercooler at daylight tomorrow as well. Here’s to hoping its that instead

 

The main fuse breaking is probably coincidence. If you unplug your battery to change the the main fuse or the negative battery cable of course the codes will disappear.

your alternator seems to be working fine. The voltages are in range. It operates higher than a traditional system and will fluctuate depending on how discharged your battery is.

the code came back because the issue was not fixed. After disconnecting the battery your emissions monitors are reset, which includes catalytic convertor.

you are right about the Cruze being a smart system but it is not considered a high voltage vehicle. If you are getting a code for p0420. Chances are very high that you have a bad convertor.

don’t cheap out and buy an off brand converter unless you want to pay twice. the Cruze doesn’t like anything but OEM converters.

 

I can’t find any intake leaks. But I did notice the exhaust sounds like this, not sure if it’s normal. This is stock, no mods

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I drove it down the street and back and it blew 2 qts of oil all over the passenger side engine compartment. Only code is still p0420. My eggs are cooked lol. Any idea on what the issue is I’ll appreciate it. I guess a front main seal. I don’t know.

 

I drove it down the street and back and it blew all 4.5 qts of oil all over the passenger side engine compartment. Only code is still p0420. My eggs are cooked lol. Any idea on what the issue is I’ll appreciate it. I guess a front main seal. I don’t know.

Like there was no warning whatsoever that this was going to happen

 

Just an update. Had a short in the coil pack connector so instead of splicing a new connector in, I replaced the entire wiring harness. You can get it cheaper from some dealerships than others. Driven 500 miles and no check engine light. I didn’t even clear it. Just hasn’t come back

 

Yes, I've just had a coil pack go bad on my 1.8l. reduced fuel economy for 3 months now until the coil finally gave out.

And with everything OEM's... I had an aftermarket pack that blew...put in an OEM coil pack and what I presumed was extra vibration at idle and sub 2000rpm acceleration, and transmission rattle. Was from having and aluminum flywheel, was infact the coil pack not being the right one.


With the heavier flywheel it hid the short comings of a cheaper pack. The coil pack provides spark, and flame rectified verification for the knock sensor array.

 

update, p0420 code came back but after running two cans of seafoam in the car the light went off by itself again

 

I've been keeping up with this thread in secret for 2 months. Same code for the cat. Ran catacleaner and it did nothing but I did also replace my coil packs about 4 months or so ago. Going to give seafoam a try and then replace my coil packs again as while i went for a 200mile drive (not the smartest but hey) i lost control to the ecm, got the stabilitrak crap etc so im assuming it started to dump fuel into my exhaust. Will try to remember and update this after i've driven with the seafoam and again if I end up changing my coil pack.

Some symptoms for me include slightly rattly(not so much that I think components inside the cat are broke) sound at higher rpm(right around 4k ), greatly reduced fuel economy and the car struggles to accelerate. I'm also going to trace my exhaust from underneath and see if theres a crack or hole anywhere.

 

I made a whole new post about p0420