Eric's Autos: Car Lingo
The 02 sensors sample the exhaust stream as it flows past, noting its chemical composition. This, in turn tells the OBD II computer whether the engine is running within spec and not too rich (excess gas in the air-fuel mix) and so on, which is critical for both emissions control and top performance/efficiency. If an O2 sensors goes bad, the computer is no longer receiving the data it needs - or receiving bad data - and a trouble code will get thrown and the "check engine" light will come on.
The upside is that with OBD - and a scan tool - it is possible for a technician to know whether the car has a bad 02 sensor rather than guess. The trouble code he pulls from the OBD II diagnostic port will tell him yes - or no.
You can do this yourself, too. Easily and fairly inexpensively. A hand-held OBD II scan tool costs about $120 (the better ones give you the code as well as tell you what the code means) and anyone who can turn an ignition key has the necessary skills to plug it into the OBD II port and pull the codes. Even if you don't want to do the actual repair work yourself, having the scan tool - and knowing what codes have been thrown can be very helpful when discussing your problem with a shop. You'll know, for example, that they're bullshitting you if they claim the OBD computer is telling them you've got "x" issue when you checked yourself and found the problem is actually "y".
* Transaxle (vs. transmission and axle) -
This refers to the transmission/axle assembly in a front-wheel-drive (or front-wheel-drive-based) car. The two components are bolted together, rather than (as in a rear-drive, or rear-drive-based car) mounted separately.
Usually, the transaxle is removed (and rebuilt/replaced) as a single unit if major service is required. In contrast, if the car is rear-drive, the transmission is one thing - and the axle another. They are located in different parts of the car (axle in back, transmission up front, with a long driveshaft connecting the two). If your car is a rear-drive car, the service guy shouldn't be talking to you about problems with the transaxle. And if your car is front-wheel-drive, there should be no talk of "rear axle" issues. (There are some rear-drive cars with transaxles; the old VW Beetle, for example. Also some high-performance sports cars.)
* Timing chain vs. timing belt -
Both do the same job - time the motion of the valvetrain (camshaft, intake and exhaust valves) in syncopation with the rotation of the crankshaft (which in turn is turned by the up and down motion of the pistons, which are bolted to it via connecting rods). This timing must be very accurate for the engine to run properly. Or at all.
The valves need to open - and close - at just the right moment to either seal the combustion chamber (there are eight combustion chambers in a V8, six if it's a six-cylinder engine - and so on) or allow air/fuel to enter - and spent exhaust gasses to escape.
The timing chain - or belt - keeps this dance happening by connecting the spinning crankshaft (being spun by the force of the explosions in the combustion chambers that drive the pistons up and down) to the also spinning camshaft (which rotates at a different rate). The camshaft (or camshafts, if it's a double overhead cam engine) causes the valves to open and close. If the timing is off, the valves will open too soon - or too late.
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