CARB approves heavy-duty OBD amendments, adopts REAL NOx & CO₂ tracking

16 November 2018

The California Air Resources Board (CARB) adopted revisions to the Heavy-Duty On-board Diagnostic (HD OBD) regulation. Among the revisions, CARB approved Real Emissions Assessment Logging (REAL) requirements that involve the collection of NOx and CO₂ emission data in real driving.

The REAL program would require OBD systems to collect and store NOx emissions data on medium- and heavy-duty diesel vehicles in-use starting in the 2022 model year. It would also require OBD systems to collect and store fuel consumption data that would be used to characterize CO₂ emissions on all heavy-duty vehicles in-use. Storage of similar data for greenhouse gas emissions is already required on light-duty and medium-duty vehicles starting in model year 2019. The REAL data will be retrieved from the vehicle by plugging a scan tool or data reader into the vehicle.

Currently, to get a snapshot of how vehicles are performing in terms of emissions, CARB either brings them to laboratories for testing or equips a handful of vehicles with portable emissions measurement systems (PEMS) equipment to find high emitters on the road.

“REAL will provide the ability to monitor all vehicles for emissions performance, and allow us to spot trouble faster. Had this program been available sooner, we would likely have recognized widespread, serious problems with manufacturers such as Volkswagen and Cummins much earlier,” said CARB Executive Officer Richard Corey.

The REAL program would require that NOx data be provided at a frequency of at least 1 Hz and integrated to show the total NOx mass and total engine output energy over the cycle. The NOx mass parameters would need to have an error of less than either 20% or 0.10 g/bhp-hr.

The REAL program will require no new technology since it will take advantage of existing sensors to track the necessary data, CARB said. Older vehicles will not be part of the REAL program and will not require any new equipment.

The adopted HD OBD amendments include a number of other revisions:

• In-use monitor performance ratio (IUMPR) requirements—The monitoring frequency of several OBD monitors would be increased 0.100 to 0.300. New IUMPR monitors would be added, including diesel EGR system high/low flow, boost pressure control system over/under boost, PM filter frequent regeneration, missing substrate, and gasoline A/F ratio cylinder imbalance.
• Intrusive diagnostics—Intrusive diagnostics would only be allowed after the MIL light is illuminated, to determine the cause of the malfunction. Intrusive diagnostics performs actions that result in increased emissions (e.g., actions that stop urea dosing in order to diagnose SCR system malfunctions).
• Other revisions to a number of monitors and test-out provisions, including diesel exhaust gas sensor (NOx sensor) monitoring, monitoring of diesel NOx converting catalyst, NOx adsorber, NMHC catalyst, EGR catalyst, PM filter, infrequent regeneration adjustment factors (IRAF), and diesel misfire monitoring.

The amendments represent one of the most important revisions to the HD OBD program. The HD OBD regulation was first adopted in 2005, and was applicable to heavy-duty engines since the 2010 model year.

CARB also approved certain revisions to the light-duty OBD II regulation to harmonize with the amended HD OBD regulation.

Source: CARB