P1256 problem P1256 what part do I need to replace

Make .................
Model .................

That code generally refers to a problem with the engine coolant temp sensor not giving the expected temperature to the computer within a specific amount of time if I remember correctly. I could be wrong but I think if you replace the thermostat the car will warm up faster and once you erase the code it shouldn't come back. Not a bad idea to replace that part anyway as part of regular maintenance and it could save your engine's life. Cheap part ($10-$15 bucks) and fairly easy to install on most vehicles. Might not be a bad idea to install a new temp sensor while you're at it, they do fail and are not very expensive either.

Autozone says the top five reasons you get a check engine light comes on is:
O2 sensor needs replacing
Gas cap is loose, damaged, or needs replaced
Catalytic converter needs replaced
Mass air flow sensor needs cleaned or replaced
The spark plug or spark plug wires need replaced.
However, it is important to note that some Miatas may have a problem where the problem is caused by an improperly tightened fuel cap. However, due to improperly manufactured threads on the fuel filler pipe, the filler pipe may need to be replaced.

the coolant temperature sensor

• Boots only need replaced when they have been negated and are leaking grease. However, the time effort and money to replace just one boot when the other is right there might bite you if the other boot needs replaced in the near future. However, if upon inspection the boot is not torn, worn and the knuckle still performs well you do not need to replace that boot.

• Hope this helps.
  

From this website:
http://www.obd-codes.com/trouble_codes/
You can click on the VW symbol to get VW unique codes.
Unfortunately, it doesn't give much information on the problem, except:
P1256 Engine Coolant Temperature Sensor Open/Short To Positive
So it could be a bad temperature sensor, or a wiring problem?

The computer sends a 5 volt reference to the sensor. Then the sensor sends back a voltage reading from.5 to5. volts depending on the temperture of the engine. you can turn the car on and check for the 5 volt reference at the plug, If you have a three wire plug one wire will have 12+ volts, the other shoud have 5 volts. If you do not get the 5 volt, the you will have to check the wire for a break in the line, typically it happens at the plug.you can check continuity of both wires going to the computer. you should get a schematic of the wiring, it will make it easier, you have to pull the plugs from the sensor and computer and use an ohm meter to check continuity. if the wires check out the the short is in the computer. replace the computer, if the short is in the wire replace the wire by running a new one of the same gauge, this is easier than tearing apart the harness to find the short

you need to reset the ECM/

replace bulb from back of assembly

shack

ITS VERY EASY, DISCONNECT THE NEGATIVE BATTERY, UNPLUG THE O2 SENSOR WIRE PRESSING THE TAB AND USING A 22 mm. WRENCH LOOSE THE SENSOR LIKE A BOLT