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Went through my daughters 05 Focus today and see she is now throwing two codes. The P0420 I know about and have decided to ignore until before next emission test in the summer. The new code is P0442 - evap emission control leak small. The car is running just fine but if it's something simple as a cracked vacuum hose I would like to fix it.

Are there common failure points on these vehicles where I should start checking first?
 

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Went through my daughters 05 Focus today and see she is now throwing two codes. The P0420 I know about and have decided to ignore until before next emission test in the summer. The new code is P0442 - evap emission control leak small. The car is running just fine but if it's something simple as a cracked vacuum hose I would like to fix it.

Are there common failure points on these vehicles where I should start checking first?
You can fabricate your own smoke test machine with just a few parts, many of which you might have lying around the house (check YouTube). The consumable is just regular mineral oil. Hook it up to a 12V battery and use a bike pump to push the smoke through your brake booster line to see if you can pinpoint the leak. Also, the P0420 code points to the bank 1 O2 sensor or the catalytic converter. By far, the cheaper of the two is the 02 sensor and if that's what it is and you let it go for too long, that can cause damage to the cat so I would try to address that as soon as you can also.
 

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X2 on running the 420 code longer, you may cause it to be permanent requiring the cat to be changed. Bank 1 sensor TWO is the second one, and the one you are concerned with.

Fuel tank cap either loose or a bad seal on it is the most common cause of a small evap leak.

One can use a cheap Harbor Freight base tire air compressor for the smoke machine pump, I've gotten them for as low as $6 before and perfect for that.
 

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Thanks for the ideas on the cheap home smoke machine. I think I have half the parts already and now this gives me the excuse to go buy the rest.

Regarding the P0420, it's been on for about a year. I played around last year trying to fix. Replaced the O2 sensor with no change. The cat is the issue. I haven't determined if I'm willing to throw the cash at a replacement yet.
 

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If the cat gets completely clogged then the engine will burn valves FYI. But by then it won't be running likely anyway. It CAN get worse, the damage is time based.
 
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