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

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Feb 13, 2025 | 07:16 PM

BottleFedBoy

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

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:

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

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

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.
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!

Last edited by BottleFedBoy; Mar 8, 2026 at 02:24 PM.