He needs to describe what alarm - there is 4 of them as for sounds. One alarm sound is dedicated for the gear lube bottle low gear oil only. That one alarm does not mean anything else but Low gear lube. Since his alarm goes away at idle it most likely not the dedicated gear lube low alarm so you are correct.

Added info on top of

ANd when scanning that fault code will show but not under low gear lube fault, it shows under another fault explanation - Anyone know what that would be ??

Other causes for this exact alarm --- The switch can go bad or The float can go bad in these as well. Also the float can get stuck to the bottom sounding off gear lube low oil alarm when in fact the gear oil is at the correct level. When one does not clean out the thick oil gel at the bottom of the reservoir - the float can stick sounding the alarm.

there is 236 fault codes and not counting any for DTS codes. And for the apps that have DTS there is NO IAC nor an alarm nor a IAC code for it. No IAC muffler for DTS either. Easily a third of all merc 496s have DTS. The OP has a lot of info missing including year model and engine serial number.

So for the Merc 496 owners how many different alarms is there that one can have at any given moment to go off ? How many things can make a alarm go off on a Merc 496 ? If you are unsure take a guess

first lets ask --- 496 mag what ? Mercruiser ? Volvo Penta ? Indmar ?

IMPORTANT can you reach full WOT because many faults will and or can put the engine into guardian mode. This alone helps pin point the possible issues at hand without even scanning the engine.

year model ?

engine serial number ?

OEM Stock app ?

Mechanical throttle and shift or DTS ?

Alarm what does the alarm sound like ? there is 4 of them as all 4 mean different things ?

What have you done to rule out the issue at hand ?

The alarm is like a check engine lite on an auto - They all need to be scanned - since you have an alarm(s) that means you have an actual fault and that can also be more than one issue at hand.

on the play there Bup... What Merc ECM application are you testing us on? MEFI 1,2,3, etc., 555 or one of the later models like the PCM-09 ECM module ?

Further thoughts - to answer your question - I will put out another question - when scanning Merc engines that use Mefi 1 - 2 - 3, if the gear lube was low and sounding an alarm would it show on the scan as a fault ?? and if so what would that show under and the scan fault wording ?

Since I already said it would show for PCM 555 - so what fault would that show under ?

And does this same fault show for ECM 555 ? if it does show, what would those fault listing words show and be under on a scan ? Keep in mind ECM 555 has alpha outdrives and Bravo outdrives for apps so how does that change things ?

You forgot PCM 012 after PCM 09 in the mix --- haha