P0401 on 2000 Camry CE

[Tim Shepard]

Hi, I'm posting to this message board because, while I found the info helpful, while troubleshooting my car, I noticed most people just post pleas for help, without ever posting the solution as payback. Here is what I did to solve this problem on my car.

P0401 on my wife's car for a couple of months intermittent. The car ran just fine, but the CEL kept coming on. She took it in for smog (I know, I should have stopped her, $40 wasted) and of course it failed, this time for P0441,445,446 (pretty sure of those numbers) as well as P0401. First thing I realized was that she had lost the gas cap some time ago (probably after the '0401 showed up. So I replaced that, thinking problem solved.

Nope, all 4 codes showed up immediately. I reset again and they were back within a week. I bought a Chilton's book and started troubleshooting. I knew the '0401 problem was either the Vac Modulator, the EGR Valve, or the VSV.
Chiltons said to blow into the Vac Modulator and if air doesn't pass freely, it is defective, that is incorrect. Very little air will come through a properly functioning Vac modulator. The fact that any air at all makes it through probably means it is good enough to switch between vacuum and 1 atm. Stupidly, I replaced the part, which is still only available from Toyota and cost $65 (I'm starting to hate you Toyota), (For comparison, I was going to buy a new 16" chainsaw with that $65). However, after installing the modulator and resetting the codes, the CEL came back on pretty much right away.

Next I tried testing the EGR valve with a Vacuum pump I borrowed for free from Partzone (I love you Partzone). It switched OK, and I noticed the the
port I was attaching too seemed a little too small for the vacuum hose that was being used, and it didn't have any barbs so it easily slid on and off. I tie wrapped that connection so there wouldn't be any vacuum leak. The engine stumbled and died when I applied vacuum to the EGR valve (as expected).

I then reset the CEL and took the car out for a drive. After two days riding, the CEL never reappeared and we were able to smog the car. My total cost was $105 wasted on a useless smog test and an overpriced Vacuum Modulator. I'm not 100% sure what fixed the problem, but here are my bets.
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The Fuel Cap caused the Evaporative system failures, even though they still ocurred after installing a new one (85% probability)

Blind Luck (15%)
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The Vacuum Modulator somehow fixed the EGR (p0401) problem even though not right away(10%)

Exercising the EGR Valve somehow cleared an obstruction that got rid of the problem (60%)

There was a vacuum leak with the hose from the EGR Valve to the VSV because the EGR valve port did not fit tightly with the hose.(20%)

The hand of God(10%)
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If you find this helpful, please make a note in a reply. Thanks.
Tim Shepard.

[Brian R.]

Thanks for the solution/description of your problem.

(A loose or non-sealing gas cap triggers P0440)