2017 Yukon 6.2 suddenly running very rough and check engine light

[RhondaHonda]

On the way home tonight from dinner and went thru the tunnel car wash (coincidence?). A few miles after going uphill my wife’s Yukon was misfiring/bucking at low rpm. The check engine light started flashing and I got a message for the stabilitrak or forward collision being inactive as well. If I manually downshifted it into 2nd it cleared up and would run ok in higher rpms but the misfire came back when the revs came back down. Pulled it into the garage for the night and it was rough idling/knocking and I believe the check engine light was now on full time, not flashing. I shut her down and restarted and it was still doing it. I checked the oil level (good) and am posting this now. It’s got 72,000 miles now so out of warranty. I did get 2 emails right away from GM/Onstar about a powertrain issue and an emissions issue. Any ideas? I don’t have a code reader.

 

[cpayne5]

Let it sit overnight and see how it is in the morning. Best wild-guess, without knowing codes and with the info provided, is something got wet in the carwash.

 

[slacktide_bitog]

What codes?

Something got wet

 

[oldhp]

I'll bet one of the O2 sensor's and or connector's is wet.

 

[Ram02]

Lifters probably went take it to the dealer

 

[Falcon_LS]

Without any codes, it's anyone's wild guess. Start by checking the air filter box and make sure everything is bone dry. For some reason or another, wet MAF sensors wreck havoc with these, especially if you got something like a cold air intake on it. I don't think the ignition coils got wet, unless the engine bay was power washed, but I would check the insulation on the plug wires anyway.

 

[Snagglefoot]

Go buy a code reader if you are trying to avoid the shop. Don’t do trial and error stuff until you get those codes. One of the codes will indicate the misfire and the other codes will help narrow down the cause. A flashing check engine light usually comes with a misfire and is telling you not to drive the vehicle. It’s a worse condition than a steady light, not the other way around.

 

[RhondaHonda]

I started it this morning and the check engine light was flashing and the traction control light was on. After a few minutes the check engine light stayed on steadily. It sounded like it had a slight misfire. I started to drive it up my driveway and it felt down on power and the check engine light started flashing again. I parked it back in the garage and will likely have it towed to the dealer tomorrow.

I do have to wonder if the car wash was just a coincidence as it goes through the same wash at least once a week.

I’ll get a code reader today and scan it and report back.

 

[RhondaHonda]

Go buy a code reader if you are trying to avoid the shop. Don’t do trial and error stuff until you get those codes. One of the codes will indicate the misfire and the other codes will help narrow down the cause. A flashing check engine light usually comes with a misfire and is telling you not to drive the vehicle. It’s a worse condition than a steady light, not the other way around.

Got a code reader, P0306, P0206 and P0711. The P0711 is the transmission temp wire harness/sensor that oddly they extended coverage for on the 2015 and 2016s but mine doesn’t fall in that although GM indicated they may eat some of the cost. I had this one in the past and then the light went out, my dealer said to wait til it comes back on as they couldn’t do anything without the light on.

The P0206 looks to be a #6 cylinder injector circuit code and P0306 is the #6 ignition misfire code. I’m hoping this isn’t a bad lifter at 72,xxx miles. I poked around under the hood and looked at the #6 cylinder for anything obvious but didn’t go any further than that.

 

[RhondaHonda]

On further examination the area of the # 6 cylinder and up onto the intake manifold is cleaner. Maybe some water spray gets in that area from the wheel well in the car wash and some connector got wet? Should I clear the codes with the reader and see if it still does it?

 

[Snagglefoot]

I’ll punt and let the pro’s chime in.

 

[RhondaHonda]

Lifters probably went take it to the dealer

That’s what I’m really hoping to avoid. Would both a #6 injector and #6 misfire code show up on that cylinder if it was a lifter? From reading online I don’t see people having the P0206 code when the lifter fails so I’m hoping it’s something simpler.

 

[RhondaHonda]

Without any codes, it's anyone's wild guess. Start by checking the air filter box and make sure everything is bone dry. For some reason or another, wet MAF sensors wreck havoc with these, especially if you got something like a cold air intake on it. I don't think the ignition coils got wet, unless the engine bay was power washed, but I would check the insulation on the plug wires anyway.

Everything was dry in the airbox, all stock. See my pic of the cleaner area on the valve cover and intake manifold as that’s where the #6 cylinder is that’s showing the codes. I was wondering if I clear the codes and swap the coil from another cylinder if I can see if it was just the coil. I had back surgery earlier this year so I’m pretty limited on what I can do and my flexibility at this point.

 

[SatinSilver]

Yes, I’d clear the codes and swap coils. Good idea. Does the car wash do an under body wash? Also I’d send a pm to clinebarger on here.

 

[RhondaHonda]

Yes, I’d clear the codes and swap coils. Good idea. Does the car wash do an under body wash? Also I’d send a pm to clinebarger on here.

I think the membership I have includes the underbody spray but I’m not sure it actually does anything. Maybe I’ll smear some chalk underneath and see if it gets washed off. Are you guessing an O2 sensor connection getting wet?

 

[Rat407]

I think the membership I have includes the underbody spray but I’m not sure it actually does anything. Maybe I’ll smear some chalk underneath and see if it gets washed off. Are you guessing an O2 sensor connection getting wet?

All the car washes I have gone through that have the underbody spray, you can tell right away since it is the first thing that hits the vehicle as you go through.

 

[mk378]

Injector circuit means an electrical problem with the injector. Which if true leads to the cylinder not firing.

Why do you keep talking about lifters and coils?

 

[RhondaHonda]

Injector circuit means an electrical problem with the injector. Which if true leads to the cylinder not firing.

Why do you keep talking about lifters and coils?

Would the injector circuit code also cause the misfire code? I brought up lifters because it was mentioned in an earlier post and is a fairly common failure on these.

 

[mk378]

Injector circuit open-- injector doesn't operate, no fuel injected, the cylinder misses-- misfire code.

 

[PimTac]

Wouldn’t this vehicle have skid plates and splash shields underneath?