Check Engine Light

ceyl · 10-14-2012, 11:38 PM

Need some help. I've got a 2004 Yukon, 5.3 that I get a check engine light during cold weather. I've replaced the MAF, both O2's and the fuel filter. During warm weather I have no issues. As soon as it gets to 30-40 degrees the light comes on. The codes are left and right bank lean, and MAF failure. Any ideas?

fielderLS3 · 10-14-2012, 11:42 PM

How does it actually run (any misfires)? Have you checked for vacuum leaks?

ceyl · 10-15-2012, 11:49 AM

Initial start-up, if near 30 degrees it runs rough, after a couple min it runs good. Has not registered any misfire codes.

Haven't checked for vacuum leaks. Even a vacuum leak doesn't make sense to me that it only occurs when cold. This has been going on for a couple of years. It passes emissions in the summer time.

I will look for a vacuum leak.

Thanks

DaBears · 10-15-2012, 12:19 PM

might be a gasket?

ceyl · 10-15-2012, 02:05 PM

Intake gasket? I was saving that for last. Not in a big hurry to dig in that far if it's not needed.

CamaroSkooter · 10-15-2012, 02:11 PM

Are you able to read the check engine light code with a handheld scanner or OBDII reader?

ceyl · 10-15-2012, 02:45 PM

I have. Don't recall all 3 codes but 2 0f them were P0171 and P0172. I can hook up the reader again tonight and list what they were.

CamaroSkooter · 10-15-2012, 04:03 PM

P0171 and P0172

To have both of those pop up at the same time usually indicates that something's goofy with the MAF sensor or there's a vacuum issue somewhere in the system.

I'm curious, what kind of air filter are you using?

ceyl · 10-15-2012, 04:26 PM

Paper filter. I've cleaned and replaced the MAF.

CamaroSkooter · 10-15-2012, 04:30 PM

Which is strange. Have you checked for vacuum leaks in colder weather?

It could be there's a crack somewhere that only exposes in colder weather because, as you know, when stuff is cold it "shrinks" and maybe when whatever gets warm in the warmer weather, it's expanded enough to plug the vacuum leak.

But diagnosing where that leak is could become quite a hassle

derklug · 10-15-2012, 11:22 PM

Find a shop with a smoke machine that will work with you, explain the problem and see if they will check the system with the smoke machine while the engine is cold. Vac leak is the most likely cause, and I would guess the intake gasket. We have had to drag our machine out into the parking lot on cold mornings a few times, usually on Windstar 3.8's, for this issue.

ceyl · 10-16-2012, 12:20 PM

Thanks Guys for your help. I'll start chasing a vacuum leak this weekend, maybe get an intake gasket ordered just in case I can't find anything else.

Again Thanks.

10-14-2012, 11:38 PM	#1
ceyl Drives: 2012 2SS/RS M6 Join Date: Apr 2012 Location: Colorado Posts: 36	Check Engine Light Need some help. I've got a 2004 Yukon, 5.3 that I get a check engine light during cold weather. I've replaced the MAF, both O2's and the fuel filter. During warm weather I have no issues. As soon as it gets to 30-40 degrees the light comes on. The codes are left and right bank lean, and MAF failure. Any ideas? __________________ SLP TVS 2300, Kooks Long Tubes, Magnaflow 3" comp, BAP, Rotofab CAI, RX catch can, valve cover breather and 3.4" SC Pulley.

10-14-2012, 11:42 PM	#2
fielderLS3 Drives: 2016 Mazda6, 2011 Mustang 5.0 Join Date: Mar 2010 Location: Portage, Wisconsin Posts: 4,049	How does it actually run (any misfires)? Have you checked for vacuum leaks? __________________ 2022 1SS 1LE (Arrived 4/29/22) "The car is the closest thing we will ever create to something that is alive." . 2022 1SS 1LE (Coming Soon)

10-15-2012, 11:49 AM	#3
ceyl Drives: 2012 2SS/RS M6 Join Date: Apr 2012 Location: Colorado Posts: 36	Initial start-up, if near 30 degrees it runs rough, after a couple min it runs good. Has not registered any misfire codes. Haven't checked for vacuum leaks. Even a vacuum leak doesn't make sense to me that it only occurs when cold. This has been going on for a couple of years. It passes emissions in the summer time. I will look for a vacuum leak. Thanks __________________ SLP TVS 2300, Kooks Long Tubes, Magnaflow 3" comp, BAP, Rotofab CAI, RX catch can, valve cover breather and 3.4" SC Pulley.

10-15-2012, 12:19 PM	#4
DaBears Drives: 2014 Subaru Forester, 2010 Equinox Join Date: Nov 2011 Location: South Bend, IN Posts: 560	might be a gasket? __________________

10-15-2012, 02:05 PM	#5
ceyl Drives: 2012 2SS/RS M6 Join Date: Apr 2012 Location: Colorado Posts: 36	Intake gasket? I was saving that for last. Not in a big hurry to dig in that far if it's not needed. __________________ SLP TVS 2300, Kooks Long Tubes, Magnaflow 3" comp, BAP, Rotofab CAI, RX catch can, valve cover breather and 3.4" SC Pulley.

10-15-2012, 02:11 PM	#6
CamaroSkooter Retarded One-Legged Owl Drives: 2010 Black Camaro 2SS Join Date: Oct 2008 Location: San Antonio, TX Posts: 9,745	Are you able to read the check engine light code with a handheld scanner or OBDII reader? __________________ My VIN = 2G1FK1EJ9A9105017 Build Date: 04-23-2009 according to: http://www.compnine.com/vid.php

10-15-2012, 02:45 PM	#7
ceyl Drives: 2012 2SS/RS M6 Join Date: Apr 2012 Location: Colorado Posts: 36	I have. Don't recall all 3 codes but 2 0f them were P0171 and P0172. I can hook up the reader again tonight and list what they were. __________________ SLP TVS 2300, Kooks Long Tubes, Magnaflow 3" comp, BAP, Rotofab CAI, RX catch can, valve cover breather and 3.4" SC Pulley.

10-15-2012, 04:03 PM	#8
CamaroSkooter Retarded One-Legged Owl Drives: 2010 Black Camaro 2SS Join Date: Oct 2008 Location: San Antonio, TX Posts: 9,745	P0171 and P0172 To have both of those pop up at the same time usually indicates that something's goofy with the MAF sensor or there's a vacuum issue somewhere in the system. I'm curious, what kind of air filter are you using? __________________ My VIN = 2G1FK1EJ9A9105017 Build Date: 04-23-2009 according to: http://www.compnine.com/vid.php

10-15-2012, 04:26 PM	#9
ceyl Drives: 2012 2SS/RS M6 Join Date: Apr 2012 Location: Colorado Posts: 36	Paper filter. I've cleaned and replaced the MAF. __________________ SLP TVS 2300, Kooks Long Tubes, Magnaflow 3" comp, BAP, Rotofab CAI, RX catch can, valve cover breather and 3.4" SC Pulley.

10-15-2012, 04:30 PM	#10
CamaroSkooter Retarded One-Legged Owl Drives: 2010 Black Camaro 2SS Join Date: Oct 2008 Location: San Antonio, TX Posts: 9,745	Which is strange. Have you checked for vacuum leaks in colder weather? It could be there's a crack somewhere that only exposes in colder weather because, as you know, when stuff is cold it "shrinks" and maybe when whatever gets warm in the warmer weather, it's expanded enough to plug the vacuum leak. But diagnosing where that leak is could become quite a hassle __________________ My VIN = 2G1FK1EJ9A9105017 Build Date: 04-23-2009 according to: http://www.compnine.com/vid.php

10-15-2012, 11:22 PM	#11
derklug Drives: 12 Boss 302 Join Date: Sep 2009 Location: Grand Rapids, Mi Posts: 1,369	Find a shop with a smoke machine that will work with you, explain the problem and see if they will check the system with the smoke machine while the engine is cold. Vac leak is the most likely cause, and I would guess the intake gasket. We have had to drag our machine out into the parking lot on cold mornings a few times, usually on Windstar 3.8's, for this issue. __________________ The biggest mistakes in life come when you know exactly what you are doing.

10-16-2012, 12:20 PM	#12
ceyl Drives: 2012 2SS/RS M6 Join Date: Apr 2012 Location: Colorado Posts: 36	Thanks Guys for your help. I'll start chasing a vacuum leak this weekend, maybe get an intake gasket ordered just in case I can't find anything else. Again Thanks. __________________ SLP TVS 2300, Kooks Long Tubes, Magnaflow 3" comp, BAP, Rotofab CAI, RX catch can, valve cover breather and 3.4" SC Pulley.

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