Mass Air and EVAP

Alright, guys, we've got a bit of a problem. 2007 avalanche, 160k on mileage. The truck would average 21mpg on the highway until a couple days ago, and my mpg was cut in half. Started not wanting to start after fueling, idling rough in gear,  and reeking of gas at idle in gear. Had code ran at Oreillys, came back as MAF and EVAP purge solenoid. Changed both last night and nothing has changed. Got 10mpg on the wayto work this morning with hard idle at stoplights. I don't remember what the actual codes #s were. Anyone have any suggestions?? Please

Unfortunately, codes are just a guide and starting point. Just because the PCM stores a MAF code does not mean the MAF requires replacement. The FSM will have charts for each code, detailing the rest of the diagnosis procedure to follow when that code is stored. Often, the procedure will account for other, simultaneous, codes, setting a priority sequence to deal with multiple codes.

If everything was fine and suddenly two separate codes have set simultaneously, I would have a strong suspicion that the problem is something common to both circuits rather than two separate problems. For example, overfilling the fuel tank can cause flooding of the EVAP charcoal cannister, which can cause problems with purge and vent systems.

So I would suggest step 1 is to identify the stored codes. If possible, the engine parameters that were stored when the code was set might also be educational, but I don't know if your auto parts shop can do that. Second step would be to get a copy of the FSM diagnostics for those codes so you can start connecting the dots.

I guess I should add the EVAP code has been there for a hard 3-4 months. I procrastinated on that one a little bit.....

Is the truck still showing the check engine light? Was one of the codes P0449 ?

Yes and yes.

Which one did you change, the vent solenoid (under the truck) or the purge solenoid (under the hood)? P0449 refers to the vent but you mentioned the purge in your original post.

I may be wrong on the code #. I'm going to autozone after work and having them scan it, then I'll report back to you all with what it shows. But I replaced the purge solenoid behind the alternator. Everything I've read said, what ever code I got, it could be either the purge or the vent solenoid causing that particular problem.

I wouldn't be surprised if it's the EVAP Canister Vent Solenoid that's in the rear of the truck. If your Avalanche still has the original style, they're considered "maintenance" items and eventually fail. I HIGHLY recommend installing the updated version that's designed to last many times longer. It's an easy process and have done it myself. Use this guide to help determine what version is installed and how to replace it: 2007-2010 P0449 EVAP Canister Vent Solenoid TSB #09-06-04-028C

For some past reference: http://www.chevyavalanchefanclub.com/cafcna/index.php?topic=122471.0

Alright, here are the existing codes. P0102
P0443 AND P0463.

Dang, quick look at the service manual and the fact that it's those three items leads me to believe there's an electrical issue happening here. You may have a damaged or getting damaged bundle of cable near the front of the driveshaft. Take a look under the truck and see if there's any wires hanging too close to where the driveshaft will spin. I know I've heard of this issue before... let me see if I can try and find that.

Here we go... some examples (images are the main thing to look at):
https://chevroletforum.com/forum/tahoe-suburban-25/2007-suburban-fuel-level-sensor-p0463-error-code-after-replacement-60646/
https://sparkys-answers.com/2015/08/2008-gmc-yukon-reduced-power-mode-code-p0641-00-stored.html
https://www.justanswer.com/gm/73dkp-gm-tahoe-2008-chevy-tahoe-ltz-getting-following-codes.html

Ok, I had autozone clear the codes. Drove home,  with the same problems, went inside for a while, came back out, started truck up and CEL was back on. Drove to the store, had them scan again, and got code P0443. So, evap vent solenoid now??

I am still chasing a p0455!!!!!

Jbrash said:

Ok, I had autozone clear the codes. Drove home,  with the same problems, went inside for a while, came back out, started truck up and CEL was back on. Drove to the store, had them scan again, and got code P0443. So, evap vent solenoid now??

Click to expand...

Have you checked the wiring up front near the driveshaft? Make sure there's no damage down there. If it was the EVAP Vent at the rear of truck it should be throwing a P0449.

ckeene said:

I am still chasing a p0455!!!!!

Click to expand...

That's an EVAP Large Leak

What steps have you taken thus far?

These are the items listed by GM;

Fuel fill cap is left off / Loose, missing or damaged fuel fill cap
Blockage or restriction in the EVAP purge solenoid, purge pipe EVAP canister, or vapor pipe

I did check the wiringup bythe driveshaftand everything is fine.

All 3 of those codes are voltage related.

P0102 is low voltage on the MAF. Which you changed, so it has to be a wiring issue.

P443 could be a stuck purge solenoid -- but you already changed that too. So the other possibility is shorted or open wiring to the purge solenoid.

P0463 indicates a voltage reading from the fuel level sensor that is so far out of range as to be impossible.

If it's not a damaged bundle of wires as suggested by ca2kjet, then I'd be suspicious of a bad ground connection somewhere, or a bad power feed through the fuse panel/ignition switch supply.

This is a situation where a factory service manual for your 2007 would be invaluable. It not only will walk you through the step-by-step diagnosis, but it diagrams every electrical circuit, connector and ground point location.