Reisunorg

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.