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I had a water pump failure (center hub twisted out) a couple of weeks ago while running at 5,800 on the water (the pump was 1 year old). The horn came on and I shut down the engine immediately. Compression is good and oil didn't smell burnt. I just replaced the water pump (complete kit w/ housing) and also replaced thermo sensor as it looked like it had been hot. Started engine in a tank and it was peeing good. Let it run at idle for about 2 minutes then idled up to 2,500. It ran at 2,500 for about 30 seconds and then the horn came on but either warning bar came up on tach. I shut down the engine and used a laser thermometer to check surface temp and it showed 105 max. Pulled thermostat and restarted engine, again it ran about 30 seconds and horn came on. Shut down and un-plugged the new thermo sensor and restarted, again after 30 seconds I got the horn. Unplugged the oil sensor and restarted, again horn after 30 seconds. I have looked thru the service manual and can't see anything besides these 2 sensors that should turn horn on. Again I'm not getting a warning bar on tach, I did get the high temp bar when the pump failed. The engine does go into limp mode when horn comes on. Any ideas?
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Update for anyone else that might see this issue;
I checked all the values on the thermo sensor and oil pressure switch and they were within specs (at the temps and pressure measured). I check continuity to ground on thermo sensor, also good. Finally checked continuity to plug at control box also all good. Un-plugged from control box and removed hot wire from battery and let set for an hour. Started back up and horn issue is gone. My best guess is the ECU had to be re-set / powered down.
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