Rep Power: 0

I have a 2000 civic si that i just picked up and the coolang guage does not work. I was wondering if anyone had any ideas on how to go by diagnosing this and getting it fixed?

 
Rep Power: 0

Should i check the coolant sensor first and What is the easiest way to check it?

 
Rep Power: 812

usually engine light will come on for bad sensor, since its also responsible for how the car runs (it sends signals to the ecu). it could be the actual gauge or a loose wire. does anything else not work on the gauges?

 
Rep Power: 189

There are 2 coolant temp sensors, 1 for the gauge (its the single wire coolant temp sender) the other is for the ecm and that is the one that tells the ecm how hot the car is and when to turn on the fan, if the gauge is not reading then you are going to want to test the resistance of that single wire coolant temp sensor. First off lets check the simple stuff check coolant level make sure its topped up next check fuse number 15 (10 amps) in the fuse panel see if its blown if so replace it. With the key off remove the yellow/green wire off the coolant temp sender its located just behind the distributor cap. Next take a jumper wire and ground the wire you just removed and turn the key on the gauge should now jump straight to hot if it does not then your gauge is at fault or you have an open wire look for damage along this wire or if corrosion is present clean it then retry it. Now using an ohmeter measure the resistance from the top of that sensor to the positive terminal of the battery, when the engine is cold it should read around 137 ohms, next you want to read it with the engine fully warmed up it should read around 46-30 ohms if it does not then the sensor is shot replace it. The sensor for the gauge has no connection to the ecm therefore it will not tell you if it is bad or not. In fact on obd2 cars sometimes it will not even tell you if the ecm coolant 2 wire sensor is bad if it is still reading at all it will most likely not throw a code but could be way off on the true temp. I have seen it many times on obd2 cars.