Mercury 15 and 20 hp EFI warning horn and light codes
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Mercury’s 15 and 20 hp EFI FourStroke outboards use a horn and a warning light to report problems, and some faults limit the engine to 2,800 rpm to protect it. Other Mercury families use different warning systems.
Applies to: Mercury 15 and 20 hp EFI FourStroke outboards covered by operation manual 8M0165094 (2019)
How the warning shows up
The horn is under the cowl near the front of the engine, with a second horn in the remote control or key switch on remote-steer models. The warning light is on the front of the engine below the top cowl.[1]
15 and 20 hp EFI FourStroke warnings
| Warning | What it means | What the manual tells you to do |
|---|---|---|
| One-second horn at start-up | System test.[1] | Nothing to do. |
| Continuous horn for six seconds, light on | Engine overheat or low oil pressure; speed limited to 2,800 rpm.[1] | For overheating: throttle back to idle, shift to neutral and look for a steady stream from the water pump indicator hole; if there is none, stop and check the cooling water intakes. For low oil pressure: stop the engine and check the oil level. If the warning continues with good water flow or a correct oil level, the engine needs service; don’t keep running it. See an authorized dealer. |
| Six beeps, light flashing six times every five minutes | An engine sensor fault; speed limited to 2,800 rpm.[1] | The manual gives no owner step. See an authorized dealer. |
| Six beeps, six flashes every five minutes (15 hp only) | The air-intake restrictor is missing; speed limited to 2,800 rpm. Mercury notes the restrictor can’t be removed to gain power.[1] | The manual gives no owner step. |
| No horn, engine misfires at high speed | Overspeed: the engine is turning too fast.[1] | Mercury lists the usual causes: propeller ventilation, the wrong propeller pitch or diameter, a slipping propeller hub, the outboard mounted too high, trim set past vertical, or cavitation. |
Sources
Facts on this page are restated in our own words from the regulations, Coast Guard guidance and manufacturer documents below. Check the document for your exact model and year.
- Operation, Maintenance and Installation Manual: 15/20 EFI FourStrokeMercury Marine (Brunswick) · 8M0165094 (1019 eng, © 2019) · p.13-14 General Information: Recording Serial Number; Model Year Production Code; p.69-72 Warning System · retrieved
Primary publishers: Mercury Marine (Brunswick). Spotted an error? Email the address in the footer with the model and the document you are using.