After protracted negotiations the U.S. Environmental Protection Agency (EPA) has finalized onboard diagnostics (OBD) regulations for heavy-duty, on-highway vehicles. The groundwork for the final EPA regulation was set by California Air Resources Board (CARB). Back in September of 2008, CARB obtained an EPA waiver allowing the state to implement their Heavy-Duty onboard diagnostics (HDOBD). The EPA worked with CARB in setting the final regulatory standards and the result is that there are almost no differences between the current CARB and projected EPA standards. In addition to these similarities, the acronym HDOBD will be retained. Agreement was reached in December of 2008.

HDOBD will begin implementation in the NAFTA zone beginning in 2010. It will eventually apply to all highway commercial vehicles with GVWs exceeding 14,000 pounds. For 2010, each engine OEM will be required to certify at least one engine family as HDODB-compliant. By 2013, 100% of EPA-certified highway engines will be required to be HDOBD compliant. The objective of the phase-in period is to allow OEMs to iron-out glitches in the monitoring, alert, and access systems before they become universal.

HDOBD also toughens some of the emission threshold standards for commercial vehicles weighing less than 14,000 pounds. The changes are designed to embed something closer to 2010 EPA emissions thresholds into the regulation as opposed to the existing standard based on 2004 EPA levels. Key features of the proposed HDOBD include:

• Manufacturers will be required to monitor all emissions systems and when pre-programmed threshold values are exceeded, alert the vehicle operator.

• HDOBD compliant systems must log an audit trail when a malfunction occurs in a monitored emissions circuit. Typically but not universally, the alert threshold standard will be equivalent to 1.5 times the EPA standard for the build model year.

• Ensure that the information required to diagnose and repair HDOBD monitored circuits is made openly available to the service and repair industry. This means that HDOBD monitored circuits will be required to be accessed and diagnosed using generic electronic service tool (EST) diagnostics.

In the early days of highway truck electronic systems, OEMs engineered chassis electronics to be more generally accessible than their automotive counterparts. Over the years, this access has been eroded away to read-only at best. This was in part the inevitable result of the increased complexity of engine management electronics but also in recent years attributable to a calculated effort to block access by generic ESTs. HDOBD is designed to bring highway truck OEMs in line with their automotive counterparts. Similar to the automotive version, HDOBD only applies to emissions-related circuits and devices. Whether it will actually result in allowing OBD-related repairs to be made by service providers lacking access to OEM diagnostic software and ESTs remains to be seen.

Sean Bennett February 2009