The warning module of a Mariner outboard engine samples the engine temperature and oil level of the motor, the function of the engine overheating sensor, the ignition control module and the engine control module. Many of the operations conducted to troubleshoot the warning module are as simple as testing its reporting capabilities with a digital multimeter to ensure that they all work, and that there are no short or open circuits in the module.
Ensure the boat's remote control is the one specified for the motor. You can find the information for the remote control unit for the motor in the operator's manual.
Disconnect the tan and blue lead from the wiring harness at its terminal on the engine block and touch the lead to the engine block. Turn the key switch to the "on" position. If the warning horn does not sound, ensure that all leads between the warning module and the electronic control module are firmly connected.
Turn the selector of a digital multimeter to the "diode test" or "continuity test" position, usually the last position on the right. Turn the multimeter on and touch the red multimeter probe to the tan-and-blue wire on the warning module horn and the black probe to the engine block, to test for continuity. If the circuit has continuity, that is, its resistance is less than 210 ohms, replace the ECM.
Suspect the engine overheating sensor is faulty if the engine is not overheating, but the overheating warning is operating continuously. Disconnect the sensor and turn the key switch "On." If the warning continues to operate, replace the ICM. Turn the key switch on. If the engine overheat warning does not activate when you turn the key switch to the "On" position, replace the sensor as well.
Disconnect the two sensor leads from the terminal connectors located in the engine oil filler cap if a low oil warning light comes on. Put the red probe of the multimeter on one lead and the black probe on the other. There should be no continuity across the cap. If there is continuity, replace the filler cap.
- "Mariner/Mercury Outboards Repair Manual, 2.5-250 HP, 1990-2000"; Seloc Marine; 2007