P0449 And P0443 Driving Me Crazy!

AnonEMoose · September 10, 2010

On my 2007 Chevy Tahoe....First started out with "TIGHTEN GAS CAP" display on the dash....every other day or so. Then, finally the CHECK ENGINE light came on one day. I got a new gas cap at the Chevy dealer, went and had the DTC checked, which read P0449 and then reset the computer. Went another day or so alright and then the TIGHTEN GAS CAP warning came back and the CHECK ENGINE light again. Same code was set - P0449. So, I ordered and replaced the EVAP vent solenoid (which is underneath the spare tire BTW). Reset the computer again, CHECK ENGINE light stays out for a day or so, and then it's back on again. Read the code and this time and it is now P0443. I checked the electrical connections to the EVAP Purge Value and did not find anything out of the ordinary (There was +BAT voltage on the pink wire with the key on but I didn't have any tools or a way to check if the computer was actuating the ground connection). So, I ordered and replaced the EVAP Purge Valve. Had the computer reset and much to my frustration the CHECK ENGINE light is back on - with P0443 set, again!. What the heck is going???!!! There is only two things left to replace that I can think of - the Fuel Pressure Sensor in the tank and the computer itself! Or, should I just put a black sticker over the CHECK ENGINE light and call it a day. HELP!!!!!

minibike132 · September 10, 2010

Put the tape over the light.

It seems like you have a good understanding of the circuits and what you need to have. The 449 and 443 are not interconnected in any way so I would say it is a coincidence that you had both set in a matter of days. These codes have nothing to do with weather or not the system can hold vacuum, they are purely codes that indicate an electrical circuit failure for the indicated output. Looking at the diagrams the only thing that the two have in common is the pcm (where the ground signal comes from).

I hesitate to tell you to replace the pcm, that is an expensive guess without the right tools to diagnose. You might be best off in this case to explain where you are at and what you have done to someone with a tech-2 and get it diagnosed before throwing more money at it.

Without a scan tool that can control outputs you could check the individual circuits without checking the pcm itself. You didn't say how you found batt voltage at the purge. Being a solenoid that requires some amperage to push I wouldn't check the B+ side with a volt meter, I would use a light. If you are really handy you could use both and do an active circuit voltage drop (that would be my preferred method, but I'm not going to post 5 pages of instructions and theory if you are not familliar). You could check the ground circuit with the active circuit voltage drop with both sides (pcm and purge) disconnected to check that circuit too. If I didn't have the tools to activate the circuit that is what I would do to come up with the best possible educated guess.

Good luck, and if you are not already familliar with those tests don't try them. You can really dammage electronic components if you do the tests wrong.

AnonEMoose · September 10, 2010

Thanks for the tips. I don't have a test light, but I have a FLUKE digital multi-meter and a set of schematics. I checked the PINK wire from the Purge Valve connector all the way back to the fuse (and and it's getting power when the key is on). I did not ohm out the other side of the purge valve solenoid (DK GRN/WHT) back to the SOL CTRL terminal on the ECM, however. I've already been investigating the idea of where I can get my hands on a Tech-2 scan tool. I suppose in the meantime it's going to be black electrical tape over the CHECK ENGINE light until I can get it into the dealer. Something may indeed be going wrong with the computer (or that one connection I haven't been able to check).

AnonEMoose · September 10, 2010

Put the tape over the light.

It seems like you have a good understanding of the circuits and what you need to have. The 449 and 443 are not interconnected in any way so I would say it is a coincidence that you had both set in a matter of days. These codes have nothing to do with weather or not the system can hold vacuum, they are purely codes that indicate an electrical circuit failure for the indicated output. Looking at the diagrams the only thing that the two have in common is the pcm (where the ground signal comes from).

I hesitate to tell you to replace the pcm, that is an expensive guess without the right tools to diagnose. You might be best off in this case to explain where you are at and what you have done to someone with a tech-2 and get it diagnosed before throwing more money at it.

Without a scan tool that can control outputs you could check the individual circuits without checking the pcm itself. You didn't say how you found batt voltage at the purge. Being a solenoid that requires some amperage to push I wouldn't check the B+ side with a volt meter, I would use a light. If you are really handy you could use both and do an active circuit voltage drop (that would be my preferred method, but I'm not going to post 5 pages of instructions and theory if you are not familliar). You could check the ground circuit with the active circuit voltage drop with both sides (pcm and purge) disconnected to check that circuit too. If I didn't have the tools to activate the circuit that is what I would do to come up with the best possible educated guess.

Good luck, and if you are not already familliar with those tests don't try them. You can really dammage electronic components if you do the tests wrong.

Tape over the light actually was quite comforting....but I still found myself peeking to see if it was still on. I can't stand it anymore. I've made an appointment with the Chevy dealer to check things out. Something just isn't right. The reason I say that is because I took it to Autozone to read the DTC code that was set, and of course it was P0443 again. Interestingly, after that when I started the truck and pulled away, the transmission shifting seemed to be abnormal - it was jerking hard between shifts. That was totally weird. I shut the engine off, restated it and drove off and everything seemed ok. I'm not liking where this is leading...Could it be the computer going out???

minibike132 · September 10, 2010

Could it be the computer going out???

Could be, could also be a power or ground to the module or corrupted data.

AnonEMoose · September 11, 2010

Could it be the computer going out???

Could be, could also be a power or ground to the module or corrupted data.

Re-seated all the connectors to the computer and taking it to the dealer to hopefully track this down once and for all and be done with it.

AnonEMoose · September 11, 2010

Back from the dealer. Now I remember why dealers SUCK!

Mechanic told me vent tube coming out of the back of the purge solenoid was loose (which was bull sh_t!). I asked him to please check to see if the computer was actuating the solenoid properly. So, he did...he connected up his Tech-2, got out his little test light and ran through all the diagnostics to and the computer was working correctly. BUT, HE DID NOT ACTUALLY test the purge solenoid itself - which I had just replaced. But, what could I say, right? So, he supposedly put another new one on, ran the diagnostic and told me, code P0443 is still being set that he believed the vent tube needed to be replaced.

There wasn't much I could say at this point about the vent tube because I had actually previously broken the plastic snap ring retainer clip that holds it on and I had put electrical tape around the end of it to hold the clip in. So, a vacuum leak at that point was plausable, but I didn't think likely.

At this point, I was into this deal ANOTHER $200 ($147 in labor, and $53 for an over-priced solenoid). AND, they said the vent tube would be another $100!!!! I said, button it up, and I'll think about it.

Well, I went on my way, and of course the CHECK ENGINE light is on again. I went to the auto parts store to buy hose clamps and hose to 'FIX' this supposedly leaking/loose vent tube. When I popped open the hood to begin the repair I noticed two things (1) The tape I had put on the tube to hold the plastic retainer clip looked as if it had not been disturbed, AND (2) THE WIRES THAT WERE SUPPOSE TO BE CONNECTED TO THE PURGE SOLENOID WAS DISCONNECTED AND DANGLING DOWN BESIDE THE ENGINE!!!!!

I cut the end off of the vent tube and spliced everything tightly together with hose and clamps - no way this thing could be leaking now. I know the purge solenoid is working because before I reconnected all the tubing I plugged the thing back in, cranked up the engine, and put my finger over the end. About 30seconds later or so, I could feel it drawing a vacuum because of the pulsating suction on my finger.

So, what I believe just happened is I paid $200 dollars for a spare vent solenoid that I didn't need and I still have the problem.

Is it the bone head mechanics that are called in to work on Saturdays???

Could it be the computer going out???

Could be, could also be a power or ground to the module or corrupted data.

Re-seated all the connectors to the computer and taking it to the dealer to hopefully track this down once and for all and be done with it.

AnonEMoose · January 1, 2011

Put the tape over the light.

It seems like you have a good understanding of the circuits and what you need to have. The 449 and 443 are not interconnected in any way so I would say it is a coincidence that you had both set in a matter of days. These codes have nothing to do with weather or not the system can hold vacuum, they are purely codes that indicate an electrical circuit failure for the indicated output. Looking at the diagrams the only thing that the two have in common is the pcm (where the ground signal comes from).

I hesitate to tell you to replace the pcm, that is an expensive guess without the right tools to diagnose. You might be best off in this case to explain where you are at and what you have done to someone with a tech-2 and get it diagnosed before throwing more money at it.

Without a scan tool that can control outputs you could check the individual circuits without checking the pcm itself. You didn't say how you found batt voltage at the purge. Being a solenoid that requires some amperage to push I wouldn't check the B+ side with a volt meter, I would use a light. If you are really handy you could use both and do an active circuit voltage drop (that would be my preferred method, but I'm not going to post 5 pages of instructions and theory if you are not familliar). You could check the ground circuit with the active circuit voltage drop with both sides (pcm and purge) disconnected to check that circuit too. If I didn't have the tools to activate the circuit that is what I would do to come up with the best possible educated guess.

Good luck, and if you are not already familliar with those tests don't try them. You can really dammage electronic components if you do the tests wrong.

Tape over the light actually was quite comforting....but I still found myself peeking to see if it was still on. I can't stand it anymore. I've made an appointment with the Chevy dealer to check things out. Something just isn't right. The reason I say that is because I took it to Autozone to read the DTC code that was set, and of course it was P0443 again. Interestingly, after that when I started the truck and pulled away, the transmission shifting seemed to be abnormal - it was jerking hard between shifts. That was totally weird. I shut the engine off, restated it and drove off and everything seemed ok. I'm not liking where this is leading...Could it be the computer going out???

Well, it's been a while, and I thought everything was ok, then this started coming back again. I've replaced the Purge Solenoid valve at least 3 times now. I even bought a scan code reader now just for kicks....and ever so often the check engine light will come on, I put the code reader on it, and sure enough it's P0443 again. I clear the code, everything is fine for a week or so, and then it will happen again. And I clear it again and so on and so forth. Could there be some other problem that is setting P0443 besides the purge solenoid itself???

redvett · January 2, 2011

Some where you have a vacuum leak and the only way to find it is a smoke test.

minibike132 · January 2, 2011

Some where you have a vacuum leak and the only way to find it is a smoke test.

233monte · January 2, 2011

Are you sure you don't want to put another solenoid on it? 4th time might be a charm. find a reputable shop and let them FIX it, not just throw parts at it.