I have a 96 Mazda 626 V6, after many months of stuffing about with OBD i still can't get it to work. I have the code reader unit, lead that goes from the Mazda OBD port to OBD2, and scanning software (Scan Tool). The computer has all the latest driver updates and is functioning properly but the software will not find the tool... Having said this the same set up (minus the Mazda lead) works on 3 other cars i have tryed it on (2013 Toyota corolla and 2003 camry , 1998 Hyundai assent) with no problems just plug and play. Any ideas???

SOURCE: Wat is a P1407 fault code....I connected a scan

p1407 is egr system no flow

p0303 is cylinder 3 misfire

po171 is fuel control system is lean

you might want to start by checking the mass airflow sensor bolts as they tend to come loose.and that should take care of the po171. check the hoses for the egr, if all is okay possibly the egr solenoid might be faulty. for the p0303 check the sparkplug on cylinder three and the spark plug wire, if you have an ohm meter you can check the resistance of the wire by hooking up your test leads to either end of the wire (after removing it from the engine) and make note of the resistance...then replace that wire and remove another one and test it the same way.. the results should be about the same, if you compare a shorter wire then the resistance will be slightly lower...just as if you test a longer wire it will be a little more. hope this helps

SOURCE: I connected a scan tool

My advise is to look at what moistcabbage had to say about your problem. Then I will add a little advise:
Put the P0171 on hold until you have a verified fix for the other 2 codes. Here's why:
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A misfire causes raw fuel and air to be shoved down the exhaust as an unburned mixture (After all. that's what a misfire is.) This can cause the free oxygen level in the exhaust to rise and cause the lean code (P0171) From the EGR code that you have, I can tell that you have the 2.0L engine in your car. (This is not a valid code for the 2.5L) In this case, moistcabbage is sort-of correct. Thiscode actually indicates that the EGR valve does not move when the computer commands the EGR to open. (Which SHOULD also be producing a P0400 code, which is EGR no or low flow.) If P0400 is not present, then chances are that this is caused by the EGR sensor "lying" to the computer and telling it that the EGR is not opening when it really is. However, it also may be telling the truth and the computer just hasn't picked up on the low flow issue yet. Anyway, if the EGR is not moving, it could be caused by a vacuum leak, which will also cause your P0171code.
The logical order of this would be to check for obvious causes of misfire like the spark plug, wire, coil, and fuel injector and correct as necessary. Also check the EGR system out to find out what the cause of the EGR not moving code is. (And repar as necessary) Then clear the codes and drive the car to see if the P0171 code returns. If P0171 returns and the other codes stay gone, then you will have to check into oter possible causes of the lean code. Otherwise, I would not waste any time checking into a lean condition at all before the other two codes are confirmed fixed.