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I drive an old 1994 Mazda 626. It still runs great most of the time, and I am in love with it. Recently, however, the check engine light (CEL) turned on briefly, then went away. This repeated once again, and I felt it was time to take action. I took it to a local Mazda dealer (I was fed up with local mechanics, two of which screwed up simple repair jobs) and they told me it was a failed oxygen sensor. I had recently noticed my mileage was going down, from somewhere as high as 30 mpg (I drive conservatively) to the current 20~24 mpg. A failed oxygen sensor, which can behave poorly even before the CEL comes on, is one possible cause of reduced mpg.

The Mazda dealer wanted ~$220 for the part and labor. Since I had already forked over $380 for a 120K maintenance procedure (transmission flush, etc.) I wasn’t in the mood to pay an additional $220 (I need to get my rear  brakes and front CV boot/joint fixed though), so I started researching oxygen sensors.

• On the mazda626.net site, I found a wealth of information on techniques, parts, etc. The most useful piece of information I found after much reading is that on pre 1996 Mazdas (inline 4 engines), there is only one oxygen sensor. 1996 and later models have two or more, one before the catalytic converter and one after.
• Autozone sells the parts, and a oxygen sensor socket/wrench kit. They also loan them out, but it was cheap enough that I just bought the kit.
• Resetting the ECU (the computer) requires you to unhook the negative (gnd) terminal of the battery, and step on the brake pedal for more than 5 seconds.

I am away from home right now on business, but I’ve already bought all the parts and tools I need (Bosch oxygen sensor for ~$60) and am looking forward to replacing it when I get back.

(This is the second time I’m writing this, my first post inexplicably disappeared )

I get (have) to travel a lot for work, and usually I rent a car. (usually Hertz, as I am a Gold Member) Hertz used to allow me to specifically request a Mazda, but these days it is not an option. However, I have been lucky the past three times I’ve rented a car, and have gotten to drive three very different Mazdas.

• Miata (Las Vegas). Ok, this was a pleasure rental and not for business. I was surprised to find a Miata waiting for me at the canopy, as I had requested an economy car. It was a newish Miata, with a ragtop. I decided I wanted to find out what all the excitement surrounding the miata was, so I went ahead and drove it out of the lot. Immediately there were two things I didnt like about it: the seats are very low to the ground and uncomfortable, and there was a LOT of road noise. My companion liked it even less, and eventually said she hated it. Still we only had the car for a day, so it was at least a learning experience. No more Miatas!
• Mazda6 (DC). I own a 626, which is the predecessor to the Mazda6. While the 626 is squarely a family sedan, the Mazda6 is a bit smaller in interior space, and a lot more sporty in exteriors. I liked the 6 I drove, which had a V6, but could tell that a normal 4 cylinder would not have any oomph to match the sporty lines of the car. My 626 engine is nothing to gush over either, but at least the body doesn’t scream sporty like the 6 does. All in all though not a bad car. With incentives and rebates, I believe you can get a 6 for the same or lower price than a Mazda3, which is probably a good deal.
• Mazda5 (DC). This is the microvan I am currently driving this week. I’ve driven it before, and thought its acceleration was amazing considered it was a microvan, but this time around I’m not impressed with the acceleration. The gas mileage is pretty poor too. However, I think this is a very useful vehicle if I were married and had 2+ kids. Probably don’t want to make this the primary car, however. In a perfect world I would have a Mazda3 for day to day commuting and a Mazda5 for weekend trips with a family. Now all I need to do is get rich and get a family!