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Check engine codes

What does the code PO440 mean?

Should be able to Google for codes. My Toyota shop manual says:

Evaporative Emission control System Malfunction.

On My Toyota, this involves an inability to hold the gas vapors in the gas tank or move them to the charcoal canister to avoid leakage to atmosphere.

Such things as loose gas tank cap, or defective one, or leaks in hoses or charcoal canister, can cause this code. Also low pressure valves on canister assembly.

The first thing to check is to see if the gas tank cap was properly tightened. Often it isn’t.

Next, the cheapest thing is to try a new cap. You don’t get much labor for the price of a new cap.

Well, sorry, always the first thing to do is look things over. Loose hoses in engine compartment, or bent gas tank filler, anything strange that might be visible by inspection. Then, on to this list.

This on many models is tested by sucking a vacuum in the gas tank, then measuring the pressure of the tank over a period of time. If the vacuum goes away too fast, the computer assumes a leak, and turns on the light indicating something is wrong, so you can scan the codes.