Stumped...

OK, I'm usually pretty good with figuring stuff out, but this one's got me and I can't find any info. I have a 2000 GTP that's giving me the code P0449. I don't need the usual explaination for what that is, it's the EVAP system. I have the problem tracked down to specifically the canister vent solenoid. From what I've read, when the purge valve opens, which mine does and creates a vaccuum, the vent solenoid should close. I am getting ignition power to the vent, but no ground. The ground is supposed to be acitvated by the PCM when the purge valve opens. The power is there at all times. So, why am I getting no ground to the vent solenoid? That's the $64,000 question. And yes, the wire is fine, it's pin 2 on the clear connector that's dead.. something is supposed to close it. Just did a test in on that pin, it's reading 8.2k ohms at all times when the car is on, 0.L when it's off, no change when the purge solenoid opens. Thanks for any help.

James

I'm wondering if the fuel pressure sensor on top of the tank is the trigger for the vent solenoid. I hope not, the access panel is buried under two layers of dynomat and a big a$$ subwoofer box. Any help at all??? Thanks

fuel pressure sensor? Ah, im assuming you mean EVAP pressure sensor? If so, then yes it is, right on top of the sending unit.

My bad, yes the EVEP pressure sensor. Does it the trigger the PCM to close the ground for the canister vent solenoid? I'm not sure, but I believe the only way to change that sensor is to get an entire fuel pump.

Looks like correct term is "fuel tank pressure sensor".
ROCKAUTO shows it as a separate sensor. About $35 for one from Standard $60 for Delco.

Cool, Autozone right down the street from me has one for $43. But first, does anyone know the correct procedure for checking this part? ei, what voltages should be produced and under what conditions when this part is working correctly? There should be reading for cold start with purge valve closed and vent open, warmed up with purge valve open and vent closed, and operating tempurature with system maintaining vaccuum (purge valve and vent solenoid closed).

The PCM sends 5 volts to the sensor & should get back between .1 & 4.9
That's from a 99 Bonneville FSM, I'm guessing they didn't change.

I'm getting 1.48 volts when the purge valve is closed, 1.54 when it's open. I'm thinking there should be greater difference than that to trigger the vent solenoid, but I could be wrong. Then again, maybe not, it needs to see change in pressure to change the votage output.. just talking to myself here. I'll manually ground the vent and see what happens. Can't find any tech info on it.

looking at your post,maybe i can give a little info.looking at the flow chart for this code.the reason you dont have a ground is because 1 you need a tech 2 or code reader that will command the vent soleinoid on/off.and 2 the pcm has an internal driver.which means the pcm supplys ground.the way you are testing it will never get the results you want.either it has a bad vent soleinod,short to ground or bad pcm.no other way to test this.

Your proabably right about the PCM error. Manually grounding the vent solenoid got it to close and I got voltage up to 4.2 on the pressure sensor, then the purge solenoid turns off and letting it run for 30 mins it won't come back on until I turn the car off and back on. My scanner is saying "Evaporative Vent Control Circuit Intermittent". I can invoke the purge solenoid by shutting the car off and back on, but I wanted to see if it would engage on it's own. It didn't. Gotta be PCM trouble, all the harware in the circuit is working, just not the way the computer should be telling it to. This may be an opportune time to get an aftermarket one that's been reprogrammed. It's probably cheaper than a new one or having the dealer test and reprogram mine.