S300 ECU not turning on...

EconoBox · Post by **EconoBox** » Fri Oct 31, 2008 1:11 pm

I have a OBD1 P72 with an s300 installed in it. When I turn the key to on the ECU does not turn on. The little green LED doesn't light up and it isn't recognized by my lap top. The harness was recently tucked but the car ran fine when the motor was in. There is no motor in right now but I am wondering where I should start looking to figure out why it isn't turning on. I installed my ECU into my friends D15b swapped hatch and it worked fine. I have an H22a in my car so the harness is modified for the IABs and VTEC.

I have already checked the Main Relay and all of the fuses in the car. I have checked and double checked for every ground and main power to the ECU. I still can't figure out the problem. Any advice would be greatly appreciated.

One thing that I saw that bothered me was 3 cut off wires from the block off plug with all yellow/black wires. One has an open end.

Post by **Spunkster** » Fri Oct 31, 2008 4:39 pm

You have answered your own question. Your problem is with the wiring in your vehicle.

EconoBox · Post by **EconoBox** » Fri Oct 31, 2008 5:14 pm

I know the problem is with the wiring... I am trying to get an idea for the starting point of where to look. I have been checking volts and ohms all day long to no results. I have full wiring diagrams out and pin outs for everything and I can't figure it out. The car ran fine a week ago and no wiring has changed since then.

Does anyone have any diagram for the little connector on the passenger side that has all yellow/black wires going into it? I believe that is the problem it is the only thing that is not connected and reads nothing I just can't find it on my diagrams.

EconoBox · Post by **EconoBox** » Fri Oct 31, 2008 10:26 pm

The connector I am talking about is the C125 Junction Connector. Five of the wires are run for the injectors and resistor box. Then there are several wires that are not connected. If anyone knows where the wires go or has a schematic please share. I have both the Helms and the Factory Honda Technician manual and I can not figure this out. I am going crazy... I am tempted to take out the whole harness and try another one...

Jaker · Post by **Jaker** » Sun Nov 02, 2008 5:27 pm

If there is no motor in your car, then the ECU is not being grounded. The ECU ground is at the thermostat housing, and then grounded further by the grounds that run from the engine to the chassis. If you have no engine, you have no ground.

EconoBox · Post by **EconoBox** » Fri Nov 14, 2008 3:51 pm

^ I connected the grounds to the chassis and disconnected the fuel pump to test the ECU before installing the motor so the grounding wasn't the issue.

I found the problem today. finally :D

A pin on the harness under the fusebox was loose... I repinned it and it seems to have fixed everything. The missing wires I was concerned about were removed by the previous owner and connected to a couple sensors I no longer have in the car.

Thanks everyone who tried to help.