Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 371Get this manual
3 Reinstall retaining ring using suitable pair of Snap Ring Pliers
Oil Injection System Trouble Shooting Chart
TROUBLE SHOOTING THE OIL INJECTION SYSTEM
If problem occurs with the oil injection system and the warning horn sounds in pulsating manner, stop engine and check if problem is caused by (1) low oil level or (2) faulty warning sensor1Open the cowling on engine and check oil level in engine reservoir tankIf oil is not to the top of tankthe problem is low oilThere is safety reserve of oil left in the reservoir after the low oil warning is sounded that allows you enough oil for 30 to 40 minutes of full throttle operationRefer to troubleshooting chart to correct the problem