Troubleshooting NEMA 2000 Systems in Marine Engines

What corrupted digital data looks like on a NEMA 2000 system

This is what DC electricity looks like using an oscilloscope. What you are looking at in this photo above is an Evinrude E-Tec 50 HP outboard engine connected to digital gauges through a NEMA 2000 backbone connection. The photo above is what corrupted digital data looks like.

How this system works is fairly simple. The system runs off a high / low voltage system (low is 1.5 – 2.5 volts and high is 2.5 – 3.5 volts). The two voltages on the high / low mirror each other to confirm accurate data to the ECM. The resistance is 60 ohms in the NEMA 2000 backbone system. When a “T” connector, wire connection, terminator or gauge malfunctions, the data becomes corrupted and this clear high / low data can not communicate clearly. This is what causes digital gauges to not work properly, freeze, etc. Connecting the oscilloscope to the NEMA 2000 backbone allows you to see this data while you trouble shoot the system. Mirrored wavy lines is clean data. Lines that run into each other, in consistent high / low digital data (not alike on the high and low sides), and spikes in the data show that there is corrupted data. By isolating and disconnecting each “T” connector (if there are multiple backbones on board) one by one until the oscilloscope shows clean data is how you find the problem.

What clean data looks like using an oscilliscope

The data is so fast it runs on a factor of milliseconds and can not be detected using a multi-meter (only good for verifying resistance). Using an oscilloscope is the only way to confirm clean data. This system also works on CAN bus systems such as in the Mercury outboard / inboard engines.

I thought this would be helpful to anyone that may encounter this problem on their boats and what to expect and look for in the diagnosis and repair.

Capt. John Banister, AMS

Suenos Azules Marine Surveying and Consulting

Palm Beach Gardens, Florida


Views: 39


You need to be a member of BoatFlorida (South Florida) to add comments!

Join BoatFlorida (South Florida)

Newest Members


Private docks perfect for accommodating your large vessels and mega-yachts.

Boater's resource to the best boating in Miami, Ft. Lauderdale & Palm Beach with upcoming boat events & boating destinations.

Latest Activity

Robert Urso is now a member of BoatFlorida (South Florida)
Jul 28
Profile IconGil Lopez, Glen Foster, Ralph T Stallings and 6 more joined BoatFlorida (South Florida)
Jul 14
Tim Collins is now a member of BoatFlorida (South Florida)
Feb 20
Josh is now a member of BoatFlorida (South Florida)
Jan 16
JOSEPH LEHRER is now a member of BoatFlorida (South Florida)
Nov 27, 2017

Other Local Sites

Boating in Florida
Not located near Broward County? Find a local site near you!

Broward Area Fuel Prices

Limited Amount of Advertising is available. Please contact us for more details.

Follow BoatFlorida on Twitter

© 2018   Created by Rusty.   Powered by

Badges  |  Contact us  |  Terms of Service