Hondata

Car: 1999 Honda Accord EX 5spd
ECU: P28 with all capacitors replaced
S300 serial number: 67277
Mods: Ghost key push button, air intake, full speaker system

Issue: installed s300v3 onto the p28 and hooked it to my car. At first the s300 was turning on fine and I uploaded my tune to the car. Went to go finish my install and start the car but the s300 won't show any live data. At this point I could see the green lights (D4 and D3) on the s300 but D2 was flashing red rapidly. I figured it was the ECU connection with the s300 so I took it off and tried to align it better. I know the s300 is on there correctly now but when I hook it to my car I'm getting no lights on the s300 at all now. I checked the ECU fuse already and it was good. I tried to unplug everything and plug it all back in but that didn't work either. Also I'm hearing some weird clicking near the radio/climate control area. This ECU doesn't have a J12 capacitor. If I plug my original ECU back in the car works no problem

Here are some pics on the ECU

What is the battery voltage at the ECU measured with a multimeter when cranking?

I didn't even get to the cranking stage I couldn't get the s300 to power on correctly. I sent the ECU and S300 to the person I bought it from to test my combo. I'm gonna see what they say before I test any further.

Had my ECU and S300V3 set up tested, and it came back completely normal. I think there is something wrong with my car's wiring that is causing the issue. Once I get my P28 back in the mail, I will troubleshoot further. Also, I don't think the ECU is losing power but the car is rejecting the ECU after the first on-off cycle.

Spunkster wrote: Mon Aug 11, 2025 9:21 am What is the battery voltage at the ECU measured with a multimeter when cranking?

Got my ECU and S300V3 back and nothing was wrong on the ECU end so it has to be my car's setup. I tested the power at the ECU connector and I'm getting 11.8V so it's definitely getting power. My S300V3 still won't turn on. Not sure what to do now....