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2004 GMC Yukon XL... CEL intermittently coming on.

jonrpick

jonrpick

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The wife has asked that I consult CK5. I told her I'd just give her $25, but she is being lazy. :doah: :haha:


Her Yukon is intermittently turning on the CEL when she drives. It's got the 5.3L if it's relevant. Shows that it's running lean..? Before I pay some asshat mechanic to turn a wrench, I'd like to try to diagnose this or get an idea of what we're up against.

Anyone familiar with these trucks must by now know about the dash gauges randomly going nuts and then finally failing completely. We have a few doing that. It's a simple matter of replacing the stepper motors in the cluster. They're on the way already... :woot: :pimp: :saweet:

Pic of the printed output from the code scanner for reference. Ideas?

code_scanner.jpg
 
see alot of bad intake gaskets (on ls motors) causing intermittent lean codes......then again, maybe I am just an asshat mechanic.:D
 
Must be... :deal: :haha: :p:

No, unfortunately, most that I've dealt with have been in big chains, and I've had generally poor luck. Sad to say. Obviously not all are asshats, but you know what I mean.

Is there any other likely culprit? She needs to top off the coolant about once or twice a year, but I suspected it to be a worn radiator cap or something as there aren't any leaks.
 
compare the front o2s to the rears, I have seen failed upstream o2s show way lean while the downstream shows that it is not.


Does it have any noticeable driveability issues?
 
No, though there is a weird, as-far-as-I-know-unrelated problem...

The stability control will kick in randomly with going around a corner at low speeds. It happens maybe once a week, or every 2 weeks. Just for a brief couple of seconds and then goes away.

The truck runs as good as ever, at least as far as I'm aware. We got it used in 2007 and it's always been strong. The transmission still shifts well, the engine starts quickly, runs smooth. I did have to change the alternator a few weeks ago when it died suddenly driving down the road. Other than that... :dunno:

What's the best way to check the O2 sensors?
 
Wait... just realized you're not a paid member, so you may not see the attachment. I'll transcribe...

The MIL is commanded On.

Emissions-Related Powertrain DTCs, Mode 3:
Electronic Control Unit ID: 10
P0171
System too Lean (Bank 1)
P0174
System too Lean (Bank 1)

Continuously-Monitored Systems DTCs, Mode 7:
Electronic Control Unit ID: 10
P0171
System too Lean (Bank 1)
P0174
System too Lean (Bank 1)
Click to expand...
 
Does it have two upstream and two downstream o2s?

Basically have to have scan tool on it, to see what is going on before code sets.

could be bad o2, dirty injector/s, vacuum leak only affecting bank 1.
I am not super familiar with these years, around here we still work on a lot of tbi and vortec stuff.
 
Speaking of injectors... she's run a couple bottles of cheap cleaner through the tank. I've heard that most of that stuff is junk and that Sea Foam is the way to go. What are your recommendations?

The "mechanics" that looked at it today said they couldn't change the fuel filter because it was "internal". :dunno: Though every guide I've looked at online shows it being inline along the driver's side framerail. :doah:
 
I have seen some of those with no external filter.

As far as injector cleaner in the fuel, I think for that stuff to work you have to use it fairly regularly, and before they are dirty enough to cause issues.

I you think that maybe the injectors are dirty, find someone that offers injection system cleanings with a "motorvac" machine. It will get them nice and clean.
 
Can you see your short term and long term trim values? What's interesting to me is that you're setting codes on both banks, making it seem less like an exhaust leak or bad O2 sensor (I suppose they could both go bad at the same time) and more like a fuel delivery problem. All 4 of your sensors are isolated ground type (gray connector), so this probably isn't a ground strap type issue.

If it sets the code while idling it could be a vacuum leak. Do you have a fuel pressure gauge?
 
9 out of 10 times its bad intake gaskets for a P0171 AND A P0174

could be other things that were already mentioned, but its prob gaskets and it changes as tem changes.

seen rough idling and smooth idle still casue it
 
Google says that the likely culprit is a vacum leak.

I would get a can of MAF cleaner and clean the MAF first. That seems to be an underlying code setter in many instances. It can't really hurt and it's not labor intensive.

There is enough info out there on these trucks now that a good google search will lead you in the right direction.
 
i agree with 63chevyII to be lean on both banks you could have a leaky intake gasket, easyas pie to change on 5.3. to be lean on both banks i would suspect something "higher" in the chain than an 02 sensor, if that makes any sense...does in my mind :haha:

i would also check fuel pressure tho, had my cousins 5.3 set lean codes and it also ran rough at times, found out the fuel pump wasnt supplying enough pressure causing both bank lean codes and rough idle.

anyways, good luck
 
thats funny, On the deal he showed me it only said bank 1 was lean. It must not say that on the picture in the first post...I cant see it.

Yeah, if it says it is lean on both banks, most likely not an o2 problem. Like said earlier, clean maf first (its free and needs to be done anyway).

check for vac leaks at intake gaskets.
Unless you can positively find that the intake gaskets are leaking, you pretty much need to have the thing on a scan tool and watch the 02s.
 
That year of 5.3 setting 171 and 174 just screams bad intake gaskets,that and the fact that it is intermittent. The intakes leak worst when cold then seem to stop leaking as the engine warms up.
 
Having the same codes pop up on my 99. Started last month and is intermittent as well. Ive read that it can also be caused by a bad fuel sender as well as the dirty MAF, dirty injectors, intake gaskets, O2 sensors, fuel pressure, etc. I know the fuel sender in my truck needs replaced and it seems it will only throw codes when the sender malfunctions. I dont know might be just a coincidence that it happens at the same time.
 
I am almost positive that it's the intake gaskets. I've replaced a bunch of them on those trucks. The stability light could be a wheel speed sensor or the steering angle sensor. You probably can't get the code with an aftermarket scanner.
 
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