California Air Resources Board

Guidance for Engines Using the SAE J1979-2 (OBDonUDS) Protocol

Heavy-duty vehicle manufacturers that currently use the SAE J1979 communication protocol for OBD certification will transition to the SAE J1979-2 communication protocol starting with the 2027 engine model year. A small subset of Volvo and Mack vehicle models and engine families have begun this transition to the SAE J1979-2 communication protocol early starting with the 2024 model year.  

CARB’s Clean Truck Check (CTC) program will support vehicles with OBD systems certified to the SAE J1979-2 protocol. CARB is currently working with OBD device vendors to certify OBD test tools for J1979-2 vehicles in the coming months. Until such certified tools are available for sale, vehicles using the SAE J1979-2 communication protocol will be deemed to comply with CTC vehicle testing requirements. These vehicles will still be subject to all other CTC requirements.

Clean Truck Check staff are working directly with vehicle manufacturers to verify which vehicles use the SAE J1979-2 OBD communication protocol and are obtaining VINs and engine family names. If you have a Volvo or Mack vehicle with a 2024 or newer model year engine that uses the SAE 1979-2 protocol and there are no certified devices available for sale that support J1979-2, your vehicle will be deemed compliant with its upcoming testing requirement when it is within 90 days of the test due date.