Hondata

My ecu is unable to control the Radiator fan protection settings because of a wiring issue someone chopped the harness before I owned the car and there isn't a pin on my stock OBD2a Pin A27 the radiator fan clutch output, I would like to have this feature reinstalled as my stock thermostat thermistor (thermal resistor) seems to not really turn the Ran Fan Clutch even when the engine is constantly at 199 degrees Fahrenheit(while in idle heavy traffic). I've tested the ECU output and it does have a ground reference on pin 19(obd1), where would I connect this pin a27 (obd2) or pin a19 (obd1) to on the cars engine harness, I've checked the wiring diagram and found the Green wire that leads to the thermostat 2pin (thermistor). can I just connect the ECU output to that so it switches the under hood relay on by grounding out the 12v supplied on the green wire, and thus trip the high load relay to run the fan, or will this overheat the ecu? do I need a resistor between the green wire coming from the relay with 12v and the ecu ground reference and if so what size? what ohms? or am I going about this all wrong and there is another way to trip the relay for the RFC?

I would start by replacing the OEM fan switch so that it works or that properly. The ECU control is just a backup way of making it come on sooner. You should be able to wire the ECU fan control output to the fan relay (ground) to make it come on.

Sounds good, I'll check out some more b16a engine harness schematics for the wire color of the ground trip lead, do you know of any good suppository for b16a, civic 99 - 00 engine harness diagrams?

The Factor service manual is the best (Helms Manual).