I picked up a 2002 Civic Si EP3 US spec car last month. And man, who ever owned this car before me really mickey-moused everything. Anyway, I'm trying to rehab this car a bit. But currently I am having an issue with the brake & battery dash warning lights staying on. I've tried to troubleshoot, but am a bit stumped. No check engine lights.

Details about the car : stock K20A3 engine & 5spd trans. Has a kenwood stereo, 45watts max. No subs or amps or anything like that. It has an AEM V2 intake. Other than that, bone stock. Cruise & A/C currently don't work. But I imagine this is unrelated to the warning lights on dash (am I wrong?)

Things I have checked/ replaced
1. Alternator tested. Was bad. Got a new replacement.

2. Checked battery. Was weak & 6yrs old. Replaced new.

3. Checked voltage at battery when car is off =12.6v-12.8v.

4. Checked voltage at battery & connections at engine bay fuse box in between fuses & ELD. Result =14.3-14.5 volts.

5. Removed entire charge harness & unwrapped everything down to individual wires.

6. Did continuity test with a multimeter. All good. Visual check all wires. All good. Nothing cracked broken or frayed. Also grounds are good & solid.

7. Replaced ELD. It was cheap. And who knows. So did that.

8. Checked all wiring coming out of engine bay fuse box. All checks out.

9. Checked brake fluid reservoir level switch sensor with multimeter. When full no signal. When low the switch is activated. Showing continuity through sensor. So that works

10. Checked e-brake switch with multimeter. It works. Also checked e-brake adjustment. Was a bit loose. So I got rid of some of the slack. E-brake works a bit better now.

11. Checked wiring under dash going to the interior fuse box. Unplugged & re-seated & checked all fuses, relays & electrical connections to fuse box. (Pain in the bollocks).

But still no remedy. Brake & battery warning lights stay on dash at all times.

Another thing I did was to check another known good cluster. Just in case. And the problem still persisted.

Last thing I checked was what voltage the ecu was reading with a scan tool. The obd2 live data shows 12.5-13v. So this seemed like a tell to me. Alternator & battery are doing their jobs. But the true voltage being produced is not reading correctly to the ECU. I am losing 1.5v-2v some where in between the engine bay fuse box & the ecu.

I did a little searching here & other forums & youtube.

And after research I found that the Multiplex control unit inside the interior fuse box had given a few other 01-05 Civic owners some issues. Including the brake & battery lights on dash. But they say the door ding doesn't function. As well as power door locks not working.

I have the door ding. And power door locks work fine. I don't have any other electrical issues currently.

Anyway, I picked up a known good used interior box/Multiplex. But haven't installed it yet.

I'll give an update after I install the new interior fuse box/Multiplex.


But has anyone else had these issues before ? What was the solution ?

I'm trying to be smart with my diagnostics. And not just throw parts at the car. So any help is much appreciated.

 

Update: replaced the under dash fusebox/multiplex & still no fix. The brake light & battery light remain on dash.

 

So another update. I was able to pull some Abs codes. And reset the Abs light temporarily. So after resetting the Abs system, the brake light went away. But the fault codes I pulled were for a fault in the actual Abs modulator. So that needs to be replaced. So that's one half of my issue figured out.

I'm still chasing down wiring under the dash to try to figure out why my battery light is staying on. It would be great to hear some feed back from an EP3 pro on that issue.

Untill then, I'll keep providing updates.