Random Misfire (P0300) and o2 sensor codes!!

[LongrangeLauber]

Alright all, I have a continuation on this issue.

 

Took my truck to a shop before Christmas to have both Catalytic Converters replaced. I knew the driver side cat was more than likely fried due to a faulty upstream O2 sensor, as discussed early on in this thread. 

 

I had mentioned about a month ago that I was also receiving a P0430 code on top on the P0420 code. Figured if they were going to do one, might as well do both while they were in there. Picked my truck up coming up on 3 weeks now. When I got the truck back the P0430 code was still there, but the P0420 code was gone. Figured it just needed some key cycles and/ or miles put on it for it to self clear. Gave it 200ish miles as I've been told in the past and it did not go away. Figured it could be a faulty bank 2 sensor 2 O2 sensor, so grabbed an NTK branded one locally and replaced. Another 200 miles went by, code is still there. Went to clear the codes and noticed P0420 code is back again. Cleared everything and codes popped back on within 5 miles of driving.

 

So I started monitoring the O2 sensor voltages.

 

Both upstream sensors are switching back and forth between 0.000V & approximately 0.800V depending on throttle position and such.

 

Bank 1 sensor 2 holds steady right around the 0.675- 0.750V while cruising down the road and at idle after it goes into closed loop (warmed up).

 

Bank 2 sensor 2 will stay right around the same range while cruising as the other downstream sensor; But at idle, it will be a very low voltage, usually from 0.010V to 0.105V, until I hit the accelerator and it goes back to the way it should be (for the most part.)

 

Side note, I watched the Long Term Fuel Trims on my way to and from work today and at idle both banks are between +5% and +10%, but once I get cruising at a constant speed, they both pull in much closer to 0%. Lows at -1% and highs at ~+5%. From what I've read, anything in either direction of 0 in the single digits is acceptable (obviously the closer to 0% the better.)

 

Not sure what it could be at this point. I have a feeling it is something to do with a fueling issue since it keeps showing bank 2 in a lean condition at idle (according to the O2 sensor, unless there is something wrong with the new O2 sensor, but I'm sort of doubting that.

 

Plan on doing a spark plug change and a new wire set (all ACDelco branded stuff) so as I pull each spark plug out, I will go ahead and see what they look like, paying close attention to the bank 2 side of things. I have a feeling it could possibly be a faulty injector (or multiple) that could be causing the lean issue, but where it doesn't throw a misfire code. Before I go that far though I'll probably just take it into the dealer and have them figure the issue out as now I'm past due for my emissions test and just want the truck running correctly. Also have the TSB or recall about the increased pedal effort that needs to be taken care of, along with them resetting my TCCM (transfer case control module) because I have a "Service 4WD" message that pops up every time I start the truck.

[Jsdirt]

Yep you're on track with that - the post cat sensor could be telling the truth. Might have a clogged injector, or more on that bank. Usually the fuel trims will be in the double-digits positive in that case. 

 

I would suggest ANY shop over the dealer. The pay scale doesn't encourage a good diagnostic approach to issues like this. The more complex the issue, the more trips back you'll go for them to fix their misdiagnosis. And when they start winging parts, YOU pay for ALL of it. You could leave there $1,500 poorer, and have the same issue. Go to ANYONE but a dealer.

 

Is that direct-injected? I hear those are having a ton of issues over the model years, the least of which is the valve coking problem caused by the direct injection.

[LongrangeLauber]

1 hour ago, Jsdirt said:

Yep you're on track with that - the post cat sensor could be telling the truth. Might have a clogged injector, or more on that bank. Usually the fuel trims will be in the double-digits positive in that case. 

 

I would suggest ANY shop over the dealer. The pay scale doesn't encourage a good diagnostic approach to issues like this. The more complex the issue, the more trips back you'll go for them to fix their misdiagnosis. And when they start winging parts, YOU pay for ALL of it. You could leave there $1,500 poorer, and have the same issue. Go to ANYONE but a dealer.

 

Is that direct-injected? I hear those are having a ton of issues over the model years, the least of which is the valve coking problem caused by the direct injection.

Yep, direct injection L83 motor.

 

Whether it helps or not, I added a couple bottles of Chevron Techron fuel injector cleaner (each bottle handles up to 12 gallons, so two was almost enough for the tank.) Fingers crossed it helps, but not holding my breath on it. Have about 200 miles I'll be putting on the truck in the morning for work so that should help push the cleaner through the injectors.

 

The shop I originally took it to will probably be a no go for me, at least for emissions/ fuel related issues. Seems like they just hooked up their scanner, saw the 20 and 30 codes and said that yeah, you need new cats. Doubt they actually did any sort of diagnostics on the system, just followed what the scanner said.

 

I don't mind diagnosing the issue on my own, but with the modern vehicles there's so much to learn, especially with the fueling and emissions related DTC's. Oh well, I'm picking it up little by little in my spare time after work. Makes me want a nicer scanner than what I have too lol. Never had any issues like this with my 02 Silverado, only 4L60e and GM 8.6" diff problems  

[Jsdirt]

The stuff to use is BG44K for a commercial duty fuel system cleaner. They may have a newer formula for direct injected engines, but I haven't had to search for one, yet.

 

As you might remember, I've had nothing but issues with my '07, right from the test drive! Had 42 miles on the clock, and the brakes would just about give you whiplash with severe pulsation. Driver's side door trim fell off the 1st week I had it. Interior developed more interior squeaks and rattles at 2k miles than my 266k mile K1500 had. Lower ball joints didn't even reach 40k miles, engine started burning oil & front axles leaked at 50k, followed by upper ball joint failure along with one strut, then the 4x4 switch failed & hub bearings failed all before 75k, rear diff failed at 97k, transmission at 103k, and now the engine has low oil pressure getting lower with each trip at 117k. Been a lemon of lemons, lol.

 

Yeah there's quite a few shops that fire the parts cannon, too. Have to go by word-of-mouth, or read MANY reviews when picking a shop. Some are full of super sharp guys that thrive on drivability and electrical problems, and will get you out the door quickly for reasonable cash. Others aren't much different than dealers in that they'll fire the parts bazooka at the truck, empty your wallet, and never fix the problem after it sits in their shop 4 weeks or more. Really have to do your homework. I get a TON of customers frustrated with other shops and dealers doing this exact thing.

 

If you want to learn engine and electrical troubleshooting, Paul Danner is the man. He's got a website and YouTube channel - scannerdanner.com, and ScannerDanner.  He's got a Premium Channel on his website that costs $11 a month - best bang for your buck in the automotive world, hands down, full stop. I've been subbed there for 5 years now, and it's enabled me to take on hundreds of jobs I would've refused in the past. He's really sharp with this stuff. He also has a book out called Engine Performance Diagnostics that's very good to have around as a reference, too. If you have the time and are willing to learn, you can get to where you can diagnose anything on any brand without a wiring diagram just by watching his videos. He's got quite a few great ones for free on YouTube as well. His brother James owns a shop in PA, and he'll frequently film all the problem children vehicles that roll in there. 

[LongrangeLauber]

So continuation to this issue, hopefully someone reads this in the future to help them out.

 

Took truck back to shop. They assured me it was O2 sensors. Explained to them I had a couple new sensors in there already. They kept saying it was the sensors. Asked them if it wasn't the O2 sensors, will I be refunded? They told me yes. They replaced the O2 sensors. I picked up the truck Friday evening. Not even 10 miles into my drive home, CEL came back on. Called them yesterday morning and (trying to not sound like an ass) asked if they actually had the means of diagnosing this issue or if they were just throwing parts at it and hoping something sticks. Even said if you all cannot figure it out, I will take it to the dealership and have them figure it out. They said bring it back in. Took it back the same day (yesterday) and told them I think it's a fueling or ignition issue and maybe focus on that. So that's where I'm at.

 

I do not think they really like me there. Oh well, last time I use them. I just want them to fix the issue I took it in there for the first time. I'm sure I will be getting a hefty refund or a large credit towards the part/ parts that may actually be bad/ faulty. I've been trying to be nice but they're not taking anything I'm telling them seriously so it's costing them money, because I'm not paying for the parts cannon. 

 

I will keep this updated as it progresses and hopefully get to a solution 

[Jsdirt]

Wow, that sucks. Sorry to hear that. It's places just like this that give the rest of us all a bad name. Some diags can be real tough, though, so it's not surprising that it's difficult to find people that enjoy repairing these kinds of issues.

 

There's a possibility the engine computer has flaked out, too. I always find it extremely difficult to make that call here, since I'm always wondering if I missed something. You have to exhaust literally every single diagnostic avenue before calling a computer. Never an easy call to make.

 

They're fairly reasonably priced at GM compared to say, a Volvo, where one computer can cost $2,000, and is EXTREMELY easy to turn into a paperweight with the incorrect programming inputs. Nightmare of nightmares. 

 

Hope you get this straightened out soon. Keep us posted. 

[LongrangeLauber]

 

8 minutes ago, Jsdirt said:

Wow, that sucks. Sorry to hear that. It's places just like this that give the rest of us all a bad name. Some diags can be real tough, though, so it's not surprising that it's difficult to find people that enjoy repairing these kinds of issues.

 

There's a possibility the engine computer has flaked out, too. I always find it extremely difficult to make that call here, since I'm always wondering if I missed something. You have to exhaust literally every single diagnostic avenue before calling a computer. Never an easy call to make.

 

They're fairly reasonably priced at GM compared to say, a Volvo, where one computer can cost $2,000, and is EXTREMELY easy to turn into a paperweight with the incorrect programming inputs. Nightmare of nightmares. 

 

Hope you get this straightened out soon. Keep us posted. 

 

I was wondering if my ECM flaked out as well. That thought has always been in the back of my head ever since these issues started. Any idea what it would cost for a new one? I'm sure the programming portion is the most expensive part. 

 

I'm wondering if a bad ground could cause an odd issue like this. But you would figure a bad ground would cause all sorts of issues and not just an emissions issue. If they cannot figure it out, I'm sure the stealership can.

 

No doubt this is a tough issue to diagnose. I've been trying to keep cool, but I don't think this shop is actually going through an extensive list and diagnosing each system accordingly. Seems like they're just going off of probable cause and acting off of that.

[Jsdirt]

Just a quick lookup showed them between $190 $260 or so - not too bad. Programming will depend on the shop - prices are all over the place. They will have to pay for downloading the program from GM's service site. Most shops will buy the yearly subscription at $2k or so. They'll bill for that plus hourly.

 

https://www.gmpartsdirect.com/search?search_str=PCM

Edited February 22, 2022 by Jsdirt

[LongrangeLauber]

Finally bit the bullet and took it to the dealership this afternoon. I had checked all the traces for all 4 oxygen sensors from the ECM and fuse block and all of them had continuity and only about 0.1 ohms of resistance max, so that indicates to me that all the wiring for them is fine.

 

My best guess is either some of the new oxygen sensors are just no good or the ECM has something going on internally. I’m expecting it to be the latter of the two.

 

Hopefully I’ll get a call about it tomorrow sometime!

[Jsdirt]

I hope you have better luck than most - I hear nothing but horror stories from customers & people all over the internet who went to dealers. They're usually not very good at troubleshooting due to the way GM pays. 

 

Curious to see what the issue is. Hopefully you have a better dealer there. Fingers are crossed for ya. 

[Maine2500HD]

On 3/17/2022 at 9:49 PM, rdnckhntr94 said:

Finally bit the bullet and took it to the dealership this afternoon. I had checked all the traces for all 4 oxygen sensors from the ECM and fuse block and all of them had continuity and only about 0.1 ohms of resistance max, so that indicates to me that all the wiring for them is fine.

 

My best guess is either some of the new oxygen sensors are just no good or the ECM has something going on internally. I’m expecting it to be the latter of the two.

 

Hopefully I’ll get a call about it tomorrow sometime!

What did you find?  I have nearly the identical problem with my 2014

[LongrangeLauber]

9 minutes ago, Maine2500HD said:

What did you find?  I have nearly the identical problem with my 2014

Dealership told me the aftermarket cats weren’t performing as well as OEM cats. Haven’t replaced them yet just because of the money it costs. 
 

They told me they couldn’t proceed with the diagnosis until I replaced them with the OEM cats. So either it’s the cats or it could possibly be something else.

[Jsdirt]

Unreal. I've heard them all. Any way to ensure a deep 4-figure bill. Maybe these use the downstream sensors in the fueling strategy? Not sure.

 

I'd highly suggest finding some locals on any automotive forum and see who the electrical troubleshooting guru is within a reasonable driving distance. I think it would be worth it for you to hit up Ivan at Pine Hollow Auto Diagnostics in State College, PA - he could probably make an interesting video with it, too. He'd get that thing figured out, hands down, without replacing the cats. Would be WELL worth the drive and whatever he charges. He won't screw you. He's a genius with this kind of thing. Tell him Smitty sent you.

 

His email is: [email protected]  - I don't know his phone number off hand, but in one of his videos you can probably find it. https://www.youtube.com/c/PineHollowAutoDiagnostics/videos

[LongrangeLauber]

Essentially they want the truck back to OEM before proceeding with diagnosis. It may very well be the aftermarket (Magnaflow) cats still causing issues for me. I won’t know though until I purchase a new OEM y-pipe and install it. If it fixes it, then I could contact Magnaflow and request a refund since they claim to have a warranty that the parts are guaranteed for your vehicle to pass emissions or your money back.

 

Been looking around online at the OEM part and they’re all roughly the same price, seeing if there’s anywhere close enough where I could just pick it up and save the freight since that seems to be where I’m not saving money compared to ordering locally from a dealership.

[Jsdirt]

If they're plugged up from melting, that would definitely be an issue, and if it was misfiring long enough, that's a possibility. I'd look at their warranty closely, since they might not honor it if there's a misfire happening.