The check engine light (service engine soon) comes on and stays on when a problem is detected by the self diagnosis system of your vehicle. Generally, the problem is in the emissions or something that is affecting the effectiveness of the emissions, but other causes can trigger the light to come on, too. To determine the cause, the vehicle will need to be taken to a parts store or a shop that has an OBD2 scanner, or for 1995 and earlier models, an OBD1 scanner, While a scanner will not give you the magic answer, it will give you a code that narrows down the problem area.
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It is run off of the same fuse as the engine computer.
Check the engine thermostat.
If your heater does not work on your 94 Mazda Protege, check the thermostat. You can also check the heater fuse to ensure it has not blown.
Have vehicle scanned at auto parts store--most will do this free
Trouble code P0171 means:System too lean (bank 1)
If your check engine light is on - get the engine checked by a qualified mechanic - don't try turning the light off - it is telling you there is a fault in your engine.
it is a camshaft position sensor check vaccume lines also as for some reason this will throw this cone because of rough idle
It means you have a malfunction in the cars engine. If it blinks stop ASAP!.. You need a scanner to pull the codes to get to what exactly is wrong
Check the polarity of the etho port
check on youtube
Trouble code P0171 means :System too lean (bank 1)