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P0446 CEL - no other codes - 03 Highlander 2.4L

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OK, so every few engine starts I get a P0446 code.

The car is a 2003 Highlander 2.4L (FWD)

I have tried the following:

1. Replace the GAS CAP with Toyota OEM
2. replaced all of the EVAP hoses at the engine compartment and near the charcoal canister
3. Replaced the both of the VSV valves near the air filter.

My next guess was going to the charcoal canister, but that is significantly more expensive than the other parts.

Does anyone know how to CONFIRM what part it is? (other than taking it to a dealer or shop with more elaborate test equipment)?
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The elaborate test equipment (with bi-directional controls, to trigger the various valves) and tech info subscription (to see which to trigger and when) is about the only non-parts-cannon approach.

But the parts cannon isn't so expensive for one more part -- check to see if you have yet another electrically controlled valve ON the charcoal canister. According to the shop I use, 95+% of the EVAP codes in Toyota (and GM, for that matter) is due to problems with this valve.

Unfortunately, the code includes the word "circuit" ("Evaporative emission control system vent control circuit malfunction") which can be a wiring problem... and that sort of brings us full circle, because to see whether wiring is the issue, you either need a lot of test light experience + a wiring diagram, or bi-directional diagnostic equipment and tech info.

The ringer here is that the EVAP solenoids appear to me to all be PWM (pulse-width modulated). You need a noid light or a test light that the manufacturer assures you will visibly pulse with PWM circuit operation.

It's possible however, that the canister-mounted solenoid is a simple on/off type... I don't know for sure, because I don't have access to all the details. The time to replace that solenoid is in my near future, but I haven't had the time to run down all the details.

There's a problem with sourcing the valve if you're going the used part route. Sellers on ebay make it very confusing whether they are selling the charcoal canister-mounted vent solenoid, or the vent solenoid mounted on the airbox. Most sell just the latter, since it's dead easy to pull from a donor car, where the canister-mounted one, not so much.
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