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Author Topic:   Diagnosis of Cause of Alarm Sounding
nats posted 05-24-2013 11:45 AM ET (US)   Profile for nats   Send Email to nats  
I have a [2006 Boston Whaler 17-foot boat] with a Mecury 90-HP FOURSTROKE outboard. Yesterday I changed oil in the gear case. I ran the engine, and everything seemed fine. The next day the [aural alert] alarm was going off. I had to disconnect the battery to get it to stop. Any ideas? The boat is on the trailer in the driveway. [There is] no key in it, and the alarm was sounding.
jimh posted 05-24-2013 12:21 PM ET (US)     Profile for jimh  Send Email to jimh     
In any alarm system, when an alarm occurs there are three possibilities:

--there is a malfunction, the alarm system has detected the malfunction, and it is giving a proper signal;

--there is no malfunction, but a sensor is bad, signaling a false alarm; or,

--there is no malfunction, all sensors are good, but the alarm system itself is malfunctioning.

Use these possible situations as your guide to diagnosis of the cause of the constant alarm signal.

It is common that an aural alarm in an outboard motor will be used to alert the operator to several alarm conditions. Check the owner's manual to see if the manufactuerer has explained precisely what conditions will trigger an aural alarm. In some motors the cadence of the aural alarm is modified in order to provide a way for the operator to interpret the meaning of the alarm signal. The different alarm signal cadences are usually explained in the owner's manual.

On some outboard motor there are visual indicators which provide additional information to allow the operator to diagnose the alarm condition after having been alerted to it by the aural alarm. The owner's manual will explain how to interpret these additional visual indicators, if they are used.

If your engine uses an aural alarm to be an alert to several conditions, and if there is no variation in the alarm cadence, and if there are not other visual indicators to differentiate between the several possible causes, I don't know of any way to determine the specific meaning of the alarm. You will have to investigate all the possible sources which might trigger the alarm to discover if any of them are the likely source. Your owner's manual should provide some advice. The proper action to take in response to an alarm should be detailed in the owner's manual.

In diagnosis of the cause of the alarm, it is best to carefully check for an actual fault condition before considering the alarm to be a false alarm.

If a false alarm is suspected, it is usually possible to perform a test of the sensors without having to operate the engine. For example, you can test a temperature sensor by removing it from the engine and checking its electrical response to varying temperature. Or, you can check the sensor in a static test, with the engine not operating.

If a problem in the alarm system itself is suspected, it may be possible to disconnect the sensors and see it the alarm persists without input from the sensors. This is usually a good indicator that the problem is in the alarm system, not in the sensors. A common alarm system failure is the warning device itself.

I am not familiar with your specific motor or its alarm circuit. Generally a continuously sounding alarm comes from a temperature sensor.
There are several possible modes of failure in this situation:

--there is an alarm condition, the alarm is sounding properly, and you have failed to detect the alarm condition;

--there is no alarm condition, the alarm is false, and you have a electrical failure in the alarm circuitry.

If the first case, you have to look for some actual malfunction in the engine. If the second case, the electrical failure in the alarm circuitry can be located in

--a failed sensor which is falsely signaling an alarm to the alarm module

--a failed alarm module which is falsely signaling the alarm sounder

--a failed alarm sounder which is falsely signaling an alarm without actual alarm input

To test for the first case, locate the temperature sensor and disconnect it from the alarm system. If this quiets the alarm, then the sensor is bad. If this does not quiet the alarm, look for other alarm sensors and disconnect them individually, check to see if they quiet the alarm. If you find that disconnecting a sensor will quiet the alarm, then it is likely that the problem is localized to that sensor.

If the alarm persists even with sensors disconnected, the alarm may be coming from the alarm module itself. Locate the alarm sounder. Disconnect the alarm module input lead from the sensor. If this quiets the alarm, then the alarm sounder is working properly and the alarm is being generated in the alarm module. Service or replace the alarm module. If the alarm persists with the alarm module disconnected from the alarm sounder, then the alarm sounder has malfunctioned. Service or replace the alarm sounder.

An aural alert alarm sounder associated with an outboard engine typically gets its power to operate from the engine. It is very unusual for an aural alert sounder to operate when the ignition switch for the outboard engine is in the OFF position, as this normally removes all power from the alarm circuit. Perhaps the alarm is sounding because there is a problem in the ignition key switch.

jimh posted 05-26-2013 11:42 AM ET (US)     Profile for jimh  Send Email to jimh     
I do not think that changing the lubricating oil in the gear case could be causal in producing the alarm. As far as I know, there are no electrical sensors in the gear case.

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