2010 LX PZEV 4cyl sedan - horn beeps single intermittent alarm confirm when left locked

VIN# ***3831 horn wiring diagram uploaded. This alarm is integrated into the MICU, only audible output is via the horn & hood latch has no sensor. So MICU alone can sound the horn even without clockspring invoking. Already checked /swapped the relay & fuse as well as performed parasitic draw test. No CEL, hard reset & removing all remote batteries also didn't help. Only one rear stop light is bad & awaiting 7443 bulb ordered online. Interestingly stop light power is connected to the horn circuit.

Likely causes both involve MICU:

1. Battery drain causing low backup voltage causing legit chirps. But normal voltage is 12.6V & starting voltage never below 10V.
2. Bad MICU that I don't want to replace & reprogram on a hunch.

Proposed solutions, I am capable of performing both tasks neatly:

1. Install a LED switch on horn ground that I can turn off when exiting & turn back on after entering car. LED to remind me of current switch state. Horn will not confirm alarm lock & unlock but that's ok.
2. Put a tap on an ignition powered fuse (eg: accessory/wiper/washer etc) to replace RED horn relay power source on nearby vacant relay slot along with YEL & GRN. Switch original 20A horn fuse on new line & replace it with 5A fuse for stop light alone.

Prior owner had a 'minor' accident so I am leaning on a MICU chirp disable. I have repaired everything else perfectly, the beautiful magenta paint with 2-tone tan interior looks lovely. Any advice will really help!

 

Can you explain how it should work and how it currently behaves?

 

On the title - horn beeps single intermittent alarm confirmation when left locked

 

I'm not familiar with how the 2010 accord behaves locking the car to enable the security. The title is vague, and I didn't want to guess on what is happening.

Typically on Accords, when the fob locks the doors, the horn or chrip happens immedately. Does this always happen on your car? Or is the security not arming? Does the incorrect intermittent beep happen when you first lock the doors, or randomly anytime after?

Your accord should have a hood switch as part of the latch. Why is it missing or was it bypassed? Any chance the accident was on the front of the vehicle?

 

The alarm confirms arming like it should, first with a locking sound from actuators & on 2nd press of remote lock button, an audible horn signal. The intermittent beeps come randomly later when the car is locked. This LX sedan does not have a hood latch sensor, not even a wire leading to the hood. If there was one I would have closed it to lock position.

Carfax description of accident attached - looks like sides. The car was repainted but all glass panels & VIN decals intact. There is no CEL or error code from my basic OBD2 scanner. I have checked all accessible ground points are okay, the battery is old but does put out 12.6V & never below 10V with starting load. Also no parasitic load but sometimes it does a long start with crank but no start. Checked purge valve is fine.

The car was in MA & NH (snow belt) now in NJ after I got it, did notice plastic panels were pulled ruthlessly with broken & missing clips (now replaced) to spray some black anti rust compound.

 

This will be tricky as the problem is intermittent, where you'd have to catch the car in the act of messing up. The way the shop manual reads, if an input like the door switch behaves like the door is open, then the alarm will sound for ~2 minutes. So if the door switch momentarily grounded and signaled to the MICU to sound the alarm, I don't know if that will cause the MICU to chirp or go full alarm.

I'm not a fan of modifying the wiring permanently especially on newer cars. Maybe something temporary until you figure out the problem, like getting an extension that would plug into the horn fuse then have a fuse and an in-line switch to temporarily kill the horns.

I don't have a definitive answer for you, so I can only give some suggestions.

Maybe go with process of elimination, so unplug a door switch at a time, then the trunk switch. If the problem goes away, then maybe one of those switches has partial contact. I don't see in the shop manual I have where the LX doesn't have a hood switch, so I'd assume the LX has one. I might be 100% wrong about this as I'm only going off of the shop manual. A door switch could be messed up or have damaged wiring as the car was hit from the side.

If you had a scanner that can plot the various inputs to the MICU, then you might see a quick spike the might make the MICU chirp.

I remember seeing/reading where water leaking inside the car could corrode some connections near the fuse box. You may want to inspect the connectors to the MICU to look for any corrosion or a possible loose or opened spade connector making a poor connection.

This could be a tough one to figure out.

 

Thanks for your experienced guidance PAhonda. Today I checked & tightened all ground points including some which I couldn't see but used the feel of my fingers & an open box wrench. The OE ground straps are thick so I am not worried about slight surface corrosion as long as no breaking strands. I also checked voltage against power at all ground points & they are the same as across the battery terminals. Only the transmission strap was slightly loose at the body end but not any more.

When replacing the broken brake/stop lamp I will again check the aftermarket backup camera circuit connected to the reverse lamp but I saw last time that it only gets voltage on reverse.

 

While replacing the brake/stop 7443 bulb I noticed both filaments looked intact although the glass bulb itself was dark & cloudy inside. Upon testing the stop light didn't glow up but the brake light did. Multimeter shows continuity across stop bulb terminals indicating a parallel short much like a shunt resistor.

Either that or the tightened ground points caused the intermittent beeping to disappear. I posted this rather weird problem on all the Honda forums I could access & only PAhonda responded with valuable guidelines from his experience. Thanks much PAhonda, helped me stay on course.

 

Glad I could help. Is the issue resolved now?

 

Yes thanks PAhonda. I am happy to be able to fix up this last remaining problem in the car.