I have no power to relay fuel pump
If you have no power on both sides then you either have a blown circuit or an open one in the main power supply. one side should be hot all the time and the other hot only when the engine is cranking or running, grounds are ECM controlled on this vehicle.
How can I detect the ecm and correct the problem
Use a digital volt meter, hook up the positive wire to the battery and the ground wire to the fuel pump relay ground wire, turn on key you should get a voltage for a few seconds then it will go away, if you don' t get a voltage reading then there is either a broken wire from the ECM to the relay or the ECM has lost the fuel pump relay driver inside the ECM.
What is the ECM
Engine control module.
Looking for a Used Rodeo in your area?
CarGurus has 210 nationwide Rodeo listings starting at $1,250.
Search Isuzu Rodeo Questions
Isuzu Rodeo Experts