Relying on the electronic data from a truck’s engine computer may not be the most accurate gauge of fuel economy, according to a not-for profit engineering and research group for the North America trucking industry.

The report from Performance Innovation Transport Group details electronic control module data precision and accuracy between engine manufacturers and among engine models from a single manufacturer.

The study compares engine ECM data with actual test track fuel consumption and was conducted in the fall of 2014 on 14 different vehicles with engines from four manufacturers. The test track evaluations, which followed the Joint TMC/SAE Fuel Consumption Test Procedure Type II, compared fuel consumption data provided by the engine ECMs, a procedure that is generally regarded as an industry standard for testing.

“The ability to measure fuel consumption accurately and precisely and defend the results is critical for writing vehicle specifications, for establishing effective maintenance practices, and for training drivers to operate vehicles as fuel efficiently as possible,” said Yves Provencher, director of PIT Group. “Our tests show that engine ECMs present different levels of precision and accuracy, and that ECM data should be used with caution for evaluating the impact of a fuel saving technology or operational practice.”

A copy of the full PIT Group technical report is on its website.

PIT Group is a subsidiary of FPInnovations, formed in 2008, to provide what it says is an unbiased, neutral testing organization to help manufacturers evaluate and refine prototypes and fleet managers select the best technologies to reduce costs and environmental impact.