Using RPM to Synchronize DDEC Reports to J1939

When performing an accuracy assessment of the digital data stored on heavy trucks, reference instrumentation is compared to the reports generated by the diagnostic software for the Heavy Vehicle. This article explains a strategy to synchronize the times between the report and the reference instrumentation.


A paper assessing the timing and syncronization of different parameters from a DDEC 5 controlled truck was presented at the 2013 SAE World Congress. The paper, Timing and Synchronization of the Event Data Recorded by the Electronic Control Modules of Commercial Motor Vehicles - DDEC V, used a VBox as the reference instrumentation and showed that some of the switch events (brake and clutch) can be delayed over 1 second. This paper provides much of the inspiration for this work.


There are two primary objectives for this work: 1) Acquire a set of correlated data of the operation of a DDEC 6 controlled truck and 2) syncronize performance data with DDEC reports.

Correlated Data

Robust data sets that time correlate as many measurements as possible are rare. Therefore, a significant objective of this site is to host the data collected. The J1939 data bus was used to synchronize the data. The following table lists the instruments used and their purpose.

Instruments Used in Data Collection
Device Purpose
HBM eDAQ Field Computer System

Measures analog signals (Vehicle Speed Sensor Output, Brake Pressure)

Measures switch input from pressure switch on brake pedal.

Measures motion from eGPS-200.

Measures CAN from J1939 bus.

Measures serial from J1708 bus.


Racelogic VBox 3i

Measures motion

Transmits data in a CAN message onto J1939 bus for correlation

Measures switch input from pressure switch


NeoVI Yellow

Monitors and records all bus traffic from the 9-pin Deutch connector in the cab (both J1939 and J1708).


DGTech's DPA5 The RP1210 Device used to access DDEC data with a PC.

A photograph of the instruments mounted in the cab of the truck is shown below.

Instrument Cluster

The data used for this analysis is available on this site on the page titled Correlated DDEC VI Data Set.

Synchronizing DDEC Reports

DDEC reports contains time history of data in the Hard Brake Event Record, Diagnostic Record, and Last Stop Record. These data include Vehicle Speed, Engine RPM, Clutch Status, Brake Status, Engine Load, and Diagnostic state. They are reported every second. However, the data in the truck updates quicker than every second. To determine how accurate the data in DDEC reports are, they should be compared to a reference value. However, reference values and ddec reports may differ in both time and value(i.e. the horizontal and the vertical axes are different). Therefore, a method based on Engine RPM is used to synchronized the data. The program used for this is written in Python and the code is also available. It is written in such a way as to be able to copy and paste the DDEC Reports Data directly into the Python program.

Test Procedure

As a brief overview, the following actions were performed:

  1. Acquire a truck. In this case it was a 2008 Freightliner with a Detroit Diesel Series 60 Engine and A DDEC 6 controller. The tractor had a single drive axle. It was tested as a bobtail, with 1 trailer and with 2 trailers. Recording of hooking up to the trailers was also captured.
  2. Assemble the instrument cluster. A steel frame with aluminum plates was fabricated to house all instruments. The enabled the programs nd instrumentation setup outside the test vehicle and a relatively quick installation of all the instruments.
  3. Connect the test leads to the Vehicle Speed Sensor.
  4. Connect the pressure transducers to the air lined feeding the service side of the brake chambers.
  5. Mount the GPS antennas on the roof of the cab.
  6. Baseline the system in DDEC Reports and get a list of parameters from DDDL software.
  7. Drive a battery of tests and obtain DDEC Reports after each test.



Example Analysis