How can a mechanic pull codes if the CHECK ENGINE light isn't on????
 

I have a 90 RX-7 that failed emmisions... (running very rich) The mechanic did a test, and on the bill it says I have codes 11,12,18. Those are TPS, narrow AND full range, and an air temp sensor.
How can he get those codes and my check engine light doesn't come on???
Also- The TPS tests fine, (I think), I can get 1V from the green/red wire, and the other pins have voltage/continuity, with resistance in the specified range, and a smooth sweep. (the car is rough on/off idle though)
Whats going on? Are they trying to screw me with parts??
Anyone know where the engine air thermo sensor is?
Thanks for you help guys....

You can pull the codes from your 2nd gen at any time. A write up on fc3s.org explains this for your model(89-92). If all of that reads good on your tps then I would say it is good, maybe miss adjusted. An out of adjustment tps acts a lot like a bad one. The intake air temperature sensor is a sensor that temps the air going into your engine. Since air density varies at different temperatures, your ecu wants to get it perfect. It's on the manifold somewhere, sorry T2. If you have a Haynes manual it shows how to adjust tps and location of sensor. Hope this helps!!

The air temperature sensor is the likely cause of your rich running.Also your car will throw a code even if the sensor is good--simply disconnect the device from the harness and reconnect it,e.g.your TPS

Yes, it's possible that you can have multiple sensors fail and the eng chk light may not be on all the time. A lot of times, the chk eng light flashes but don't stay on. I had to change the TPS and crank angle sensor on my Buick and the light flickered but didn't stay on.

On my 3rd gen, I replaced the air temp sensor. It's underneath the intake manifold which requires removal or at least partial removal of the manifold. It's prone to be faulty. If you change it, get a new one from the dealer and don't bother trying to clean it somehow. It's not worth taking and putting the manifold back on and taking it apart.

I am sure the 2nd gen and 3rd gen works similar. On 3rd gen, you can read the code by connecting two of the plugs on the diag port and reading the no. of flashes on your dash. This can help you confirm if all the codes were read correctly.

Only certin codes will set a check engine light. Some codes have to be triped a few times before they will turn the light on. Most cars will have codes in them when you check them. it just needs one thing to not work right for a few seconds to set a code. A lot of times you can clear these codes and they won't come back because it was just a one time thing.

Mike