Rookie here. Check Engine turned on. Where to start?

[chato de shamrock]

Hey guys. I have a 1996 240sx base, all stock and I'm a true rookie when it comes to getting my hands dirty fixing my ride's problems on my own, and I mean a true rookie. I was driving to work yesterday morning and noticed the check engine light (or according the the owner's manual, the malfunction indicator light [MIL]) turned on. I've kept my eye on the fluids and all but the coolant were full. As a matter of fact, the coolant reservoir was almost bone dry, but the radiator was nice and full that morning. I added coolant later that afternoon but in the morning while driving to work I noticed the check engine light turn on. Now the owners manual indicates it might be an emissions control problem. I did what only my rookie skills were able to do, check the gas cap to make sure its on tight. It seemed to be fine, but the light is still on. Where can I go from here?

I've been searching for an info I can find and noticed you can pick up a lead if you check the car's ECU and decode the blinking light. I noticed that the info I was running into was for S13's but I'm assuming it can be applied for S14's. I found this link on a thread from a different website that was discussing S13 problems:
KA24DEvelopment.com :: ECU Diagnostics (http://www.ka24development.com/ecu_codes.html)

Can this link be applied for S14's? I could not find any info on where to locate the ECU on my car so I'll follow what this website indicates. Now, like i mentioned, i'm a rookie but i'd like to have a clue as to what may be the problem here and then take it from there. I'd like to try doing (the simple) things myself before taking the car into a shop. Are there any suggestions you guys may want to offer as to where to get started on trying to pinpoint this problem?

Also, can someone explain why Nissan added the "O/D Off" indicator light? It's always on in my car. Shouldn't they have put an "O/D On" light instead? It's like putting a "cruise control off" light thats always on except those times when you turn on your cruise control. It doesn't make sense to me :tweak:

As always, thanks for taking the time to read my threads.

[projectRDM]

I'll be nice. I shouldn't, but I will just this once.

Your ECU is behind the passenger side kick panel. Remove it, two M6 bolts and one M6 nut hold it in. Turn it around, there's a dial on the backside. Turn the key to 'on', turn the dial all the way one way, then all the way back. You'll get a series of flashes to indicate a code. Then look the code up online. Since it's OBD-II it's a standard code.

99% of the time a CEL (MIL) is emissions related, it has no bearing on fluid levels, oil pressure, overheating, poor idle, anything that would typically be obvious. It's simply out of the specified range of proper exhaust output, outside the range of what the EPA calls safe. Most of the OBD-II sensors don't even affect driveability.

O/D off is indicated because in most cases, you'll want the O/D on. It's more economical.

[devnull]

Do yourself a favor and get a code scanner. Then download a factory service manual.

Come back and search the forums when you've figured out where you stand with your current problem.

On a 240sx overdrive is actually 4th gear, so you wouldn't want to run around with it off normally. You'd probably only want to turn it off for driving mountain roads.