So I picked up a 99 Civic LX 5 sp to resell and am having a hard time with this wiring issue. The car runs and drives great but the radio didn't work. found that the "back-up"/ecu fuse under the hood was bad. replaced it and it pops imidiatly. After researching on here, determined if I cut the white/blue wire (constant power for radio), the fuse doesn't pop. I cut the wire right before it plugs into the ecu. Put a test light on the side of the wire coming into the ecu from the dash and it's hot. The other side of the wire coming from the ecu is grounded. I'm thinking this means the ecu is shorted interally but I'm no expert on this stuff, obviously! I don't have access to another ecu from a 99-00 to test that right now, but do you think my assumption is correct?

Also the power door locks, mirrors, and door swithed dome light won't work at all. Is this related or a whole seperate issue. Maybe the module behind the kick panel.

So again, if the white/blue wire is connected to the ecu, fuse pops. car still runs but no power to radio, acc plug, ect. If the wire is cut, fuse is fine power everywhere exept door locks (which never have power to the switch either way)

There is no aftermarket stereo, in fact no stereo in it at all and no stereo harness plugged in either.

Thanks so much for any help. I just hate the thought of buying an ecu only to determine there's a short in the locking system causine the ecu problem.

 

The wire you cut is critical for ECU memory, not just the radio. Your ECU can't store codes or learn from sensor inputs = very bad.

Also consider that the short is in the ECU connector rather than the ECU. You may be able to reveal this by unplugging the ECU connector and testing the Wht/Blu wire again for continuity to body ground. If it is still grounded, then the short is in the connector not the ECU.

Check all of the fuses for the locks, mirrors, and dome lights. These are separate circuits from the radio/clock/ECU memory circuit above.

 

thanks for helping!

so I put the test light on a hot wire and touched to the cut wire from ecu, lights up (good ground), unplug the connecter and light goes out. so I'm assuming it's in the ecu.

I've checked and rechecked every fuse, all are good.

As for the locks I can only find power on one wire going into the lock module, kind of a light green with black stripe. No power to the switch at all.

Thanks again!

 

Did you check all installed fuses for the locks, mirrors, and light for voltage to body ground at both top test tabs?

7.5A dash fuse 14
7.5A dash fuse 17
7.5A hood fuse 43
20A hood fuse 51

 

I don't have a numbered fuse diagram, but the ones I've focused on are;

underhood
back up
locks
int lights

dash
radio
acc outlet
keyless/cruise

all of which are good.

 

You'll find numbered fuse box diagrams in the FAQs sticky. Make sure you voltage test all of the ones I listed.

 

all fuses are showing over 15v with the car running so I don't see any problems there. however, the mirrors DO work, must have had the key off when I tried them. BUT the cruise does NOT work. So the car still runs great but the ecu pops the back up fuse, cruise and power locks are not working at all. light comes on on the cruise switch though. could it all be related to a bad ecu or are they completely seperate issues?
thanks again!

 

Are you testing for voltage at BOTH top tabs of the installed fuses for the power locks (51, 14) and cruise control (52, 25, 14)?

 

yes sir, all good!

 

Locks - check whether voltage from the two fuses reaches the keyless control unit behind the driver's kick panel.

Cruise - check whether the rubber stoppers that press on the cruise switches at the top of the brake and clutch pedals have fallen out or are damaged.