tvtahoe

I have a 2007 chevy tahoe ltz 5.3l flex fuel. The p0449 code came on in the car over the winter and never came off. I originally just tried clearing the code but it would immediately come back on. After reading on here about these cars having the common issue with the evap canister vent valve solenoid I assumed that that was my case as well. I first tested the purge solenoid which tested fine, so I ordered the new acdelco part (pn: 20995472) and the wiring harness adapter (pn: 19257603). After installing the the new parts I attempted to clear the code with my code reader and it comes right back on almost instantly. What else could this be? I know that the charcol canister is in good shape because the car is almost never over 3/4 tank full (b/c its a gas hog). The car has just over 100,000 miles on it and is only driven maybe twice a week if that. The wiring all looked fine, ill check for any cracked or damaged hoses under it as soon as it quits raining here. I will also check the fuses as well just rule anything out there. I doubt that this has any effect on the electrical for the evap system but the compressor and air shocks are failing; which should be replaced by next week as soon as the parts arrive. Thank you guys in advance for any help with my issue.

tvtahoe

Any ideas anyone?

titantn24

It could still be the canister.

tech2

the fact that the code reset immediately tells me its an electronic fault. for the canister to be at fault a evap test would have to run and fail and this takes a drive cycle to complete.



battery voltage is supplied from the tcm/batt fuse in the underhood fuse block to the solenoid. With key on, engine off, check for voltage at the red/white wire.
if that's ok, you need to test that the ecm is supplying grd.
the proper way to test the grd side is to put a test light in place of the solenoid and command it on and off with a scan tool. a working circuit should turn the light on and off.
without a scan tool I would plug the solenoid in and supply grd at the white wire. if the solenoid clicks once, the grd circuit is open or the ecm driver is bad. if the solenoid doesn't click, your new part went bad.

tvtahoe

I took another look at the car today, and am no closer to getting to the bottom of things. I did get out my multi-meter and attempted to check a few things. I found no blown fuses in the engine compartment fuse panel. The reference voltage at the connector with the keys on was right about 0.15v. I also attempted to check the resistance on the evap canister vent valve solenoid (very difficult to get a good reading with the part still on the car, and the spare tire still up) I was seeing something like 0.8 04 0.08 ohms or something (relatively low resistance). If only I had an Autel MaxiDas from my wish list I would know by now.

tech2

this circuit does not use a reference voltage. It is supplied full battery voltage. The proper way to test this is with a test light. knowing it has 12volts is nice but you need to know if the circuit can carry a load...that is how gm diagnostics wants it tested.


you have confirmed a power supply problem so now you must trace it back. I would check coming out of the fuse box after the tcm/batt fuse.


you can easily rule out your solenoid by suppling it power and grd.

tvtahoe

I don't know if this helps or not, but I used my better code reader at work today and was able to pull up a few body control module related codes. The codes that the car had back on today after resetting the battery, were u0073, c0045, and p0449. Now I know that the c0045 code is for a issue with the left rear wheel speed sensor ( The wiring must have gotten bumped putting on the new bilsteins yesterday). As far as the u0073 code; what exactly does Control Module Communication Bus Off mean? Are the p0449 and u0073 related?

tech2

what module on the truck set the u code? What were the 2 digit descriptor was set after the u0073? The format is U0073 XX.


I would clear all the dtc and diagnose the ones that return.

tvtahoe

Done. The only code that is still on is the p0449. After installing my new air ride compressor i checked over the wiring and fuses again. I see no damaged wiring, and found no blown fuses. Probing the electrical connector for the evap canister vent valve I get 1.6v across the two wires. With the black negative lead of my multi-meter on the frame rail at a grounding strap; and the positive lead probing the positive wire of the electrical connector I was seeing 11.6v. At the battery I have 12.3v; so either the voltage drop is because of the positive wire in the connector, or because the dirty ground that I was using on the frame rail. Like I said as soon as I reset the check engine light the p0449 code shows up twice on my scan tool in a matter of seconds. Is there an easy way of ruling out the new part being faulty?Can i just apply 12v with some test leads to the new part to verify that it is in working order without damaging it?

Thanks for all of your help tech2

tech2

yes, test it that way. just don't leave it connected up for a long time. the ecm will time it out after a certain amount of on time.