J1939 Sensor Overview

Overview

Published and licensed by the Society of Automotive Engineers (SAE), J1939 is an in-vehicle network for data communication and diagnostics between component controllers, such as the engine, transmission, brakes, environmental controls, etc. 

The J1939 sensor is used to detect issues and faults in the vehicle. VHM (vehicle health monitoring) uses the sensor to monitor vehicle issues in real time, much like the dashboard in a car ( when the check engine light is on to alert you that it's time for preventative maintenance measures). It monitors the engine, transmission, and brakes for active trouble codes, then sends that data to the fixed-end for alert 'events' in a 'Maintenance Queue'.

Avail displays the issue in the Message column in the Maintenance queue, and sometimes includes FMI and SPN codes, along with the prioritization level of the event, for you to reference and determine a course of action for your mechanics to take. VHM prioritization levels are 1's, 2's, 3's. Emergency alarms (EAs) are a priority of '1'. Example:  When the EA switch/ EA canned message is activated in a vehicle. Priorities of ' 2' and '3' are less urgent/ more routine maintenance needs, with '3' being the lowest priority. Avail recommends referring to SAE standards and your manufacturer's manual for recommended actions.

Avail also uses J1939 beyond DTC's and VHM Reports.  We currently use J1939 for Odometer Mileage, Vehicle Speed, and - starting with Gillig's 2024 buses - for discrete inputs: Front/Rear Doors, Stop/Lift Requests, Bike Rack. 

The primary features of Avail’s Vehicle Health Monitoring (VHM) are to:

1. Monitor J1939 DTC’s
2. Monitor J1939 SPN’s, which is J1939’s name for specific data fields
3. Monitor discrete fault inputs

VHM monitoring refers to IVU (in-vehicle unit) software that interfaces with discrete inputs and J1939 messages to detect malfunctioning equipment and generate VHM alert messages to the fixed-end system. These events notify dispatchers and maintenance in real time in Operations: 

Maintenance Reporting: The data is stored after it's logged ( logged to remove the events from the Maintenance queue) in a database where it is available for your review for essential trend analysis. Select the Maintenance Reports in your Business Intelligence reporting tool to review vehicle trends:

Maintenance Issues Reporting: 

Breakdown of VHM DTC Issues:

Specific to the VHM Module, there are three types of monitors: two types are for monitoring J1939 messages and the third type is to monitor fault signals, such the fault lines from Digital Video Recorders (DVRs).  As mentioned above, the monitor types are J1939 (Value), DTC, and discrete.

FMI = Failure Mode Identifier. Used in DTC’s to specify a fault or abnormal condition that exists in the vehicle subsystem. Specifically, an FMI applies to a SPN. 

DTCs = Data Trouble Codes. A DTC is a J1939 message that a vehicle controller sends when it detects a fault. Here are key pieces of information contained in a DTC that maintenance can monitor and manage:

1. SA - identifies the component with the failure, such as the engine
2. SPN (Suspect Parameter Number) - This identifies the feature or parameter that has the failure

Gillig discretes NOW monitored via J1939

• Front and Rear Doors (Open/Close)
• Stop and Lift Requests
• ADA Lift (Wheelchair) Stowed or Deployed
• Front Bike Rate Extended

Gillig discretes NOT monitored via J1939

• EA
• Ignition
• Gooseneck Mic PTT
• Other project specific/non-standard input.
• All our discrete outputs and our spare inputs and outputs.

Currently, Gillig is the only bus manufacturer that is implementing this change, but we anticipate this to become a standard practice in the future for all bus manufacturers. To reiterate, this change does not apply to New Flyer, Proterra, and other bus manufacturers.