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Discussion Starter #1
Hello I've had these 2 codes on my daughters car now about a yr. I gave up for awhile trying to fix them but jumped back in after reading it could very likely be the vacuum pressure sensor or VPS located on firewall. Well I read how to test them that with key on you should measure with key on close to 5 volts on one prong, 2.5 volts middle prong no volts end prong which is ground. What I measured was 4.9 volts power, 4.2 volts middle prong, 0 volts ground prong. I got about these same readings even with old VPS sensor in .I will take car for a ride to see if cel light goes off but I doubt if it will. Any one else run across this problem if so what is the cure?
 

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Locate the purge valve should have a vacuum hose to intake and a hose( with green top valve in line) to the canister.
If purge valve not opening then VPS will not register purge flow.
If you disconnect the intake vacuum hose from purge vave should see the VPS voltage change.
 

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Discussion Starter #3
Where is the purge valve located ? My Haynes manual makes mention of it and does not show it. You are saying if I find the purge valve to disconnect the vacuum line going to it and then I should see a voltage change on my middle pin of my VPS?
 

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Discussion Starter #4
I spent a couple hrs. yesterday going to a salvage yard looking for the VPS vacuum pressure switch which I heard a dealer would charge $300-$400 for I got one for $5. I do not think my old one was bad but it did not check out the way it was supposed to in that when reading current to the 3 pins with key on I get 4.9 volts on pos. pin but on middle pin where I am supposed to get 2.5 volts and move with engine rpm I read about 4.8 volts it seems it does not change weather I have the VPS plugged in backprobing or just take reading right from plug w/o the VPS plugged in is this the way it is supposed to be or did I maybe get a bad VPS from salvage yard? I did notice there are 2 other valves seems right above charcoal cannister I'm wondering if one of these could be bad? I'm thinking about buying a cheap smoke machine for $35 to see if I have a vacuum leak that I am not seeing. This is becoming frustrating have spent many hrs. trying to clear these lights car will not pass emmisions but yet it does not run bad and I do not think it is polluting.
 

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Purge valve behind air box near brake reservoir.
First verify that there is engine vacuum at the VPS.
 

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Discussion Starter #6
Guess what CEL light finally went off self set. I guess it was the VPS vacuum pressure sensor. My original one when back probing the middle prong gave me a reading of about 4.2 volts and did not drop if I put a little vacuum on end of hose with my mouth needs very little vacuum to make voltage drop, second OEM part I got from salvage yard gave same reading I thought what is the likely hood of getting a bad one from a salvage yard but since it did not check out the way all my reading says it should I went to a different salvage yard and got a 3rd VPS it did'nt even have any part numbers on it but it looked the same and came off the same yr. 97 camry 4 cyl. so I tried it when I hooled it up I got more in the ballpark readings on the middle prong key on backprobing it I got 3.2 volts all reading says you should get 2.5 volts but when I did put vacuum on just with my mouth it dropped so I thought it might just work. Took it for an 8 mile ride light stayed on but in about 18 miles key off and on about 3-4 times the light went off by itself I am sooo happy I might quick run to the emmisions center tomorrow. Thank-You CJ1 for your help and I hope this story helps someone else. The car has 196,000 miles and runs like a sewing machine.
 
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