Engine light on, but not so sure the codes are pointing to the culprit

[seangolden1983]

Howdy, so I recently bought a used 2006 Yukon XL 1500 4WD and The check engine light was on, but it seemed to be running relatively fine etc, so I hadn't worried too much til the last couple weeks, I got the codes checked and they are showing a P0449 which means evaporative emission control system vent valve or solenoid has a malfunction, however I changed out the small valve on the electric throttle body, and the EVAP Canister and Solenoid and also took off the throttle body and gave it a good cleaning, yet the problem of rough idle has persisted after I let it idle for awhile seems fine while driving at higher than idle rpms, but tonight while I was checking out some more on it I was checking for any cracked vaccum lines etc, which I never found any...but I did realize that the issue happens as soon as the Radiator Fans kick on the idle drops and nearly dies and the voltage start to fluctuate up and down from the instrument panel erratically like the rpms soooo I am thinking maybe the Alternator could be bad? I also sprayed carb cleaner around the intake manifold to see if maybe the gasket had a leak etc and got no revving from that, so after all this changing of parts and such I am wondering is the issue actually electrical in nature such as the alternator or maybe even battery? I guess I am hoping that someone else here has gone thru the same issue just looking for some advice on what you would change or get checked etc, looking to do as much as I can myself. I just realize that battery and/or alternator arent going to be super cheap to do and I hate to waste any more money on this sucker, I just want to get it to idle properly and not start to putter out when the fans kick on, the last time this occured I turned the air on full blast as well just to see what would happen and to my surprise the idle smoothed out instead of falling more, the only other prob I did notice is with the A/C knob if you turn it to off it seems to actually stay on slighlty and if you turn it to 5 or max it turns it off but the pulley on engine is still engaged at that setting and if you leave the knob set to max after awhile it will actually go ahead and kick on at full blast. Thanks for any tips etc.

 

[HiHoeSilver]

Howdy, so I recently bought a used 2006 Yukon XL 1500 4WD and The check engine light was on, but it seemed to be running relatively fine etc, so I hadn't worried too much til the last couple weeks, I got the codes checked and they are showing a P0449 which means evaporative emission control system vent valve or solenoid has a malfunction, however I changed out the small valve on the electric throttle body, and the EVAP Canister and Solenoid and also took off the throttle body and gave it a good cleaning, yet the problem of rough idle has persisted after I let it idle for awhile seems fine while driving at higher than idle rpms, but tonight while I was checking out some more on it I was checking for any cracked vaccum lines etc, which I never found any...but I did realize that the issue happens as soon as the Radiator Fans kick on the idle drops and nearly dies and the voltage start to fluctuate up and down from the instrument panel erratically like the rpms soooo I am thinking maybe the Alternator could be bad? I also sprayed carb cleaner around the intake manifold to see if maybe the gasket had a leak etc and got no revving from that, so after all this changing of parts and such I am wondering is the issue actually electrical in nature such as the alternator or maybe even battery? I guess I am hoping that someone else here has gone thru the same issue just looking for some advice on what you would change or get checked etc, looking to do as much as I can myself. I just realize that battery and/or alternator arent going to be super cheap to do and I hate to waste any more money on this sucker, I just want to get it to idle properly and not start to putter out when the fans kick on, the last time this occured I turned the air on full blast as well just to see what would happen and to my surprise the idle smoothed out instead of falling more, the only other prob I did notice is with the A/C knob if you turn it to off it seems to actually stay on slighlty and if you turn it to 5 or max it turns it off but the pulley on engine is still engaged at that setting and if you leave the knob set to max after awhile it will actually go ahead and kick on at full blast. Thanks for any tips etc.

You could just hit an auto zone and have them test the alternator and battery for free, just for kicks.

 

[seangolden1983]

sounds like a plan tomorrow i didnt realize they would do anything other than check the codes for me whilst the parts were still on the vehicle

 

[HiHoeSilver]

sounds like a plan tomorrow i didnt realize they would do anything other than check the codes for me whilst the parts were still on the vehicle

The one by me will.... Worst case is you yank the alternator real quick right there.

 

[Snowbound]

That code sometimes points to a fuel cap. When the purge solenoid opens and it doesn't effect the pressure in the fuel tank, it pops a code thinking the ameboid is the problem when in reality the tank doesn't build pressure due to a faulty cap. Vacuum leaks would be the first thing I'd check but sounds like you already have that covered. And don't buy an aftermarket fuel cap. Stealership only but it's not bad, something like $23.

Turning AC on bumps the idle in the tuning based off the load of the compressor so that's prob why it clears up. You say you cleaned the throttle body but the issue may be in the idle air control motor. If that passage is dirty it can be hunting for the correct idle air flow. Might wanna pull that off and clean it out also.

 

[seangolden1983]

That code sometimes points to a fuel cap. When the purge solenoid opens and it doesn't effect the pressure in the fuel tank, it pops a code thinking the ameboid is the problem when in reality the tank doesn't build pressure due to a faulty cap. Vacuum leaks would be the first thing I'd check but sounds like you already have that covered. And don't buy an aftermarket fuel cap. Stealership only but it's not bad, something like $23.

Turning AC on bumps the idle in the tuning based off the load of the compressor so that's prob why it clears up. You say you cleaned the throttle body but the issue may be in the idle air control motor. If that passage is dirty it can be hunting for the correct idle air flow. Might wanna pull that off and clean it out also.

Ya these have the electric throttle body and it's riveted together correct me if I'm wrong but you cant get to the motor on idle air flow if so how would I go about accessing it? Also I did the gas cap already forgot to.mention that and this morning as I parked at work the idle went wild as usual but the voltage spiked to about 17 so I'm thinkin the wire off the alternator or the alternator itself and maybe when the idle drops from lack of steady voltage it trips the p0449 code for eval emission leaks since I already replaced the evap can and solenoid along with the idle air valve on top of throttle body I dunno what else it could be will let y'all know how it goes later.

 

[Snowbound]

Ya these have the electric throttle body and it's riveted together correct me if I'm wrong but you cant get to the motor on idle air flow if so how would I go about accessing it? Also I did the gas cap already forgot to.mention that and this morning as I parked at work the idle went wild as usual but the voltage spiked to about 17 so I'm thinkin the wire off the alternator or the alternator itself and maybe when the idle drops from lack of steady voltage it trips the p0449 code for eval emission leaks since I already replaced the evap can and solenoid along with the idle air valve on top of throttle body I dunno what else it could be will let y'all know how it goes later.

Oh yes, 06 is drive by wire. I wasn't thinking. Seems like I've seen a few of these evap codes related to fuel cap, that's why I mentioned it. You did use an OEM cap right?
The PCM controls the voltage output of the alternator. Perhaps you just need to clean grounds really well. I had my 05 doing some really weird stuff like throwing code for MAF and blinkers acting up, some days it didn't do anything when I turned the key to start position. Traced it down to a few bad grounds on the side of the block. Cleaned grounds and issue was gone. Granted, that was on a Duramax truck but point is grounds can do some strange things.

 

[seangolden1983]

well I had the alt/bat/and starter checked at auto zone and oreillys they all passed I was wrong about the voltage going as high as I said its more like fluctuating between 13.3-14.7ish so I went ahead and changed the plug wires cause it sounded like it had a miss, prob will go ahead and do plugs as well since it wasnt that hard for me as I thought it might be on a couple of the wires but problem persists anyway...I got the codes cleared for the heck of it and so far it hasnt tripped again....but I did notice the tensioner on the compressor does look as if it is moving a bit when truck is running so I think I may need to swap the tension arm out on the compressor, but I dunno if that is enough to be causing the issue it has idles like straight crap unless I got the air or heat running, which is exact opposite of all posts I find they complain of idle rough when air is on but mine idles rough with it off lol. I may just say screw it and see what a shop says if i change that arm and it still does it.

 

[seangolden1983]

Just a bit of update, so I swapped the plug wires, cause it sounded like it had a bit of a miss as well, but still kinda sounds that way so i reckon i will replace plugs as the ones on there look as if they could be the originals so think ill do those as well, I had the codes completely cleared a week ago roughly since i did find a bit of a vacuum leak, patched that up and the rough idle issues went bye bye, now today as i was leaving from my job the engine light came back on, so I now need to check that out and see if it is the same p0449 or not, I am betting that it is though...if so I was curious since I have already swapped out the EVAP canister and solenoid is their perhaps an o2 sensor in that vicinity yall would recommend I try to replace or would the sensors have nothing to do with the prob? I did also check for voltage to the canister and with test light it lights up so I know its getting juice to the canister so im pretty close to like ruling it out as the culprit at this point and other than bad sensors I fear the PCM may have a fried diode or something of that nature....any takers? I am up for ideas engine seems to have the lost power back since patching the leak....its more of just a nuisance as I cannot seem to identify why the code came back after a week with it off from resetting it.

 

[seangolden1983]

Also anyone know a way I could do a smoke test myself? I am wondering if maybe my fuel pressure sensor is actually the issue I just don't want to waste more money on parts etc....How much does a smoke test usually cost anyone know?