2003 f50 alarm doesn't work

[iowajosh]

I don't think this is a common problem. I can't find any info on it because searching for anything about alarms just leads to a bunch of people talking about overheating engines.

I'm trying to get my alarm to work on my f50. I've tried cranking it with the safety lanyard removed and no sound. I took the buzzer out of the control box and gave it power and it worked. I reinstalled the buzzer and removed the wires from what looks like a temp sensor on the rear of the motor and plugged the wires together and started the engine. No buzzer. Side sensor, same.

There is +12v at the yellow wire on one side of the buzzer. The other side is a pink wire that goes through the harness through the big connector and I think to the CDI box. I poked into the pink wire and connected it to ground with the key on and the buzzer sounded. Am I correct in thinking the CDI box is what controls the alarm? Thanks for any input you may have. J

[rodbolt17]

short the pink temp switch wire to ground on the engine harness side.
allow at least 20 seconds to pass. blip the throttle above 2000 RPM and listen.

[boscoe99]

There are two main alarms on your model motor. One for over temperature and one for low oil pressure. For temperature there is a switch installed in the cylinder head and for oil pressure there is a switch installed in the block.

When the switch for over temperature closes due to excessive temperature it sends a ground reference to the CDI. The CDI then grounds the pink wire to the buzzer (buzzer will sound), puts the motor into RPM reduction mode, and may turn on a warning lamp either on the motor itself or on a tachometer.

When the switch for oil pressure closes due to low oil pressure it also sends a ground reference to the CDI. The CDI then grounds the pink wire to the buzzer (buzzer will sound), puts the motor into RPM reduction mode, and may turn on a warning lamp either on the motor itself or on a tachometer.

But here's the thing. There are delays built into the system. As soon as either switch closes nothing happens immediately. For the temperature switch there is a 20 second delay built in. Test the system by disconnecting the pink wire and the black wire to the switch. On the engine harness side connect the pink wire to the black wire. Start the motor and wait a bit of time. The alarm should sound.

For the oil pressure switch, disconnect the black wire to the switch. Connect the terminal at the end of the black wire to a clean unpainted section of the block. Run the motor for a bit of time. You should eventually here the buzzer buzzing.

If the buzzer does not sound for either test then try running the motor above 2000 RPM and see what is to be heard.

[rodbolt17]

for some reason some of the F motors must meet a few conditions to activate the alarm circuits in the ECU.
best I recall on the small F motors the engine RPM must have been above 2000 RPM during that key cycle to activate the ECU.
some require a temp of over 113*F and a certain RPM.

[iowajosh]

Thanks

Thank both of you gentlemen. There was a delay 15 or 20 seconds and the darned alarm went off for each test. I didn't have to rev this one up.

I know most people only are worried when the alarm goes off but I'm paranoid and I think this motor is the nicest thing I own. Thank you.

[boscoe99]

Thank you for the feed back. Glad to hear the tests were successful.

The more that you know about you motor, and the better you treat her, the better a product she will be for you.

[exeter27]

Here's a great example of follow-up. Iowajosh followed advice from those on the forum - but then took the extra step to report his findings. I too have this issue and was paranoid about my alarms - thinking my ECU was defective - when I simply need to wait longer.

Please folks - post follow up messages as they can provide great information to the next person. I was the next person for this one and am very grateful to the contributors and iowajosh.

[erniefish]

The best forum

I would like to thank the key players ( you know who you are ) for the thousands of answers on this forum, but also all the people who post questions ( some may be repetitive) the same questions or problems we all have or may see ,keeping our motors or our neighbors motor running , thanks everyone, and as said above ,the follow up reports