HOW DO CHANGE THE ECM

....wait, hold everything...follow the black battery cable to the spot where it bolts to the frame...wirebrush the lug and the spot where it attaches...get a NEW battery 2000 is TOO old...five years max or the alternator will suffer~ your ECM is doing the best it can with insufficient ground~

Check all the fuses inside the car and should be a fuse box on the firewall or fender. But grounds are a good thing to check all so and yes a battery is probly only good for about 5 years. But we do not know how old the battery is in your car. It may not be a fuse it may be a relay

The a/c relay has voltage to the coil terminal 2 and 1, the points from terminal 5 to 3 are closed have 12 volts on 5 nothing on 3. Need help

Try replaceing the relay first. The ecm is going to cost you alot more money. You need to know witch pins are closed circuits and witch ones are open circuits all so. That maybe why you are getting the readings you are

I had changed the relay same problem. I know which is the coil and contacts. I'm only getting 4.8 volts out of the ecm terminal 21/ air con.

Were is the relay located on my 2003 nissan frontier xe 2.4l 4 cylinder standard 5 speed truck?