2002 rodeo is my obd ground bad my ecu wont communicate and horn wont blow but fuse is good

Great question, im ane ECU spirt. )EFI.
what country, nobody ever says, that but gee, the OBD varies buy
COUNTRY!
Ill pretend USA. /Canada.

In the USA the car has OBD2. and you need a scan tool that works
on 2002 cars.
what engine, some engines have different ECU. radical differ..
they had like 3 engines here, other countries 9.

the scan tools connects to the 16pin, OBD2 connector at dash.
i the car is Can-bus. it needs a can-bus tool, all new tools work on canbus but old ones never do. (i have them back to 1995 and know this)
NON comms and tool is ok, not wrong tool . diagnosis.

1. Pin 16 not at 12vdc, (blown fuse)
2. ECU dead, 99% of time blown fuse to EFI. test the fuses to all EFI parts. alldata.com wiring shows that.
3. bad wiring to the DCL connector (rare) or from there to ECU
4. yes, some crappy tools have no ground on both pin 4 and 5, buy a tool that has 2 pins there. OR it will fail on some cars. seen many POS ELM327 tools that do this horror, get a tool called, INNOVA 3160 and stop guessing, this tool works on all cars.
5. barrow, rent , or buy or ask any sharp mech top scan car , his tool works.
6. Fuses that look ok can IN FACT be bad, we never assume they ar good we test them. using either method, OHMS or 12vdc on both sides, is better. see? only the voltage matters, all else punts.
7. The 3.3l communicates on pin 1 and 2..