Having owned an 02 zx3 that was replaced by an 07 zx3, I can say that the 05-07 are more reliable than their predecessors. That being said, any focus just isn't a focus without its quirks.
With the 02, there were a lot of kooky little issues - the ignition switch jamming, the underhood wiring harness igniting and causing the battery to explode (this killed the car at 72k miles in 07), and having a fair number of steering rack issues. (leaking, losing power assist, etc.) I loved the car, just felt that I got a bad example of the breed. (I did buy it in early 04 with 23k miles on it. When it died in 07, I bought another focus in the hopes that maybe it would be different this time. Mine had sat on the lot for six months when I bought it, and the problems were plentiful and stupid. The first year was absolute hell, then again, I had racked up nearly 50k miles within 18 months of buying the car - so that *may* have had something to do with it.
There's the whole hard start issue on manual transmission 05-07 foci. (Have been dealing with this since day one on the 07 - the software updates have done nothing) The alternator and battery gave out early on, was replaced under warranty (alternator) while I had to pay for the battery in 2008 with 35k on the clock. Nearly five years later, that battery and alternator are going strong and still testing as good with 98.5k on the clock. Mine has been in a few wrecks - so there have been some electrical gremlins that popped up as a result. The 5/100 bumper to bumper warranty saved my bacon when the body wiring harness released the smoke in the summer of 2011 with 68k on the clock. (would have been a $6500 repair, I got off easy with only having to pay the $100 deductible) The car has been pretty solid and dependable, repairing it is amazingly straightforward, and I would do it again. The combination of sporty feel, fuel economy, and sheer utility of the hatchback body style have earned my loyalty to these quirky little cars.
Of course, I have put a fair amount of miles on mine, used it for everything from pizza delivery (a job during the first period of unemployment in 08) to field service IT tech duty (averaged 2-3k miles a week) to commuting 50 miles a day to school, then work, and then doing salvage yard runs with it.
I'd recommend any 05-07 focus that has no signs of accident damage. The biggest issues I've had were due to accident damage that was overlooked during the repair process only to manifest itself a year later.
07 ZX3 SE MTX - enjoying every minute with it
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