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How To Put Diesel Generators In Diagnostic Mode

Most makes and models of generators need to be put in diagnostic mode to communicate to diagnostic or scan tools. Diagnostic mode allows you to keep the ECM powered to connect to a diagnostic tool. If the tool doesn’t automatically connect when you turn on the generator’s key or switch you will need to put it into diagnostic mode.

The easiest way to tell when working with a diagnostic tool is to plug in without external power and crank the engine. This will usually power the diagnostic tool and allow a connection. This lets us know we need to power the ECM to communicate with the machine when it’s not running. To do this, we will need to put the equipment in diagnostic mode.

How you put it in diagnostic mode is different for each make of generator. Below we will walk you through how to do it on a few makes we commonly see:

Diagnostic Mode On Multiquip Generators

To allow communication with the diagnostic tool with the John Deere or Isuzu engine off on models with the ECU Series Controller, you will need to enter diagnostic mode.  This is done by holding the hour check button while toggling the Off/Reset switch to Manual mode.  To exit diagnostic mode move the Off/Reset Switch.

If you do not have the ECU Series Controller you may need to remove ACC1 relay’s cover and close the contacts. To allow communication with the diagnostic tool on models with the Basler Controller, begin by turning the Main Power Toggle Switch to the “ON” position.  Press and hold the “Alarm Silence” and “Lamp Test” buttons for 5 seconds. 

Diagnostic Mode On Doosan Generators

To allow communication with the diagnostic tool with the Cummins engine off, a jumper may be necessary on the momentary diagnostic button.  This is typically accomplished by applying a jumper from orange wire W02B to the Red W012 wire on the backside of the bracket holding the button.  Button location is typically near the top of the engine block.

Diagnostic Mode On Generac Generators

To allow communication with the diagnostic tool on Generac machines, there is an ECU Override procedure.  It is typically accomplished in one of two ways.  First is a manual switch. This switch is located inside the control box.  Do not start the machine with this switch on.

The second way is through the Power Zone Controller.  This is done by putting the controller in “Stop” mode and then pressing the green “Start” button.  Do not start the engine while in ECU Override mode.

The Best Diagnostic Tools for Generators

If you are working on different makes and models of generators and need bi-directional capabilities, there aren’t many aftermarket options. Our Diesel Technicians have been very impressed with the functionality of the off-highway modules of TEXA IDC5 and Cojali Jaltest. To make the tool even more user-friendly Diesel Laptops has created complete kits with the diagnostic software, repair information, and access to tech support all on a heavy-duty tough case laptop.

If you already have the kit and need technical support our US-based team is here to help, call (888) 983-1975.

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Angaeli Lall-Butcher

Angaeli covers all things Off-Highway as a part of the marketing team at Diesel Laptops, from construction and agriculture machinery to heavy equipment diagnostics.

My role has brought me to The National Tractor Pulling Championships in Bowling Green OH, had me trekking through farms in Gilbert, SC and even sent me to a construction theme park in NJ. I spread the word about new ways that Diesel Laptops serves the Off-Highway community, and work with diesel techs to help them discover heavy equipment repair options.

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