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EPA Proposes First Onboard Diagnostic Systems (OBD) for New Large Trucks and Buses

EPA is proposing rules requiring the use of onboard diagnostic (OBD) systems to monitor the emissions control systems of large diesel and gasoline highway trucks and buses weighing more than 14,000 pounds.

Onboard diagnostic systems, used in passenger vehicles since the mid-1990s, monitor emissions control components, detect need for emission-related repairs, and alert the vehicle’s operator of these problems. They also help inform service technicians what problem exists so that it can be repaired properly. The OBD systems for highway trucks will work the same way.

The proposed requirements are part of the Clean Diesel Truck and Bus Program, which is designed to result in significant reductions of nitrogen oxides, particulate matter, non-methane hydrocarbons, carbon monoxide, sulfur dioxide, and air toxics from diesel-powered vehicles. These emission reductions will prevent 8,300 premature deaths, more than 9,500 hospitalizations, and 1.5 million lost work days, according to the EPA.

The proposal also makes changes to certain existing OBD requirements for smaller highway diesel trucks.

Specific components of the proposed rule include:

  • For 2010 and later model year heavy-duty diesel and gasoline engines used in trucks and buses over 14,000 pounds, all major emissions control systems will be monitored and malfunctions be detected prior to emissions exceeding a set of emissions thresholds. Most notably, the aftertreatment devices&mash;e.g., the diesel particulate filters and oxides of nitrogen (NOx) reducing catalysts—that will be used on highway diesel engines to comply with the 2010 emissions standards will be monitored and their failure will be detected and noted to the driver. EPA is also proposing that all emission-related electronic sensors and actuators be monitored for proper operation.

  • For 2010 and later highway vehicles over 14,000 pounds, one engine family per manufacturer will need to be certified to the proposed OBD requirements in the 2010 through 2012 model years. Beginning in 2013, all highway engines for all manufacturers would have to be certified to the proposed OBD requirements. This phase-in is designed to spread over a number of years the development effort required by industry and to provide industry with a learning period prior to implementing the OBD requirements on 100% of their highway product line.

  • For vehicles over 14,000 pounds, the service information availability requirements would apply for those engines certified to the OBD requirements.

  • For 2010 and later model year highway heavy-duty diesel vehicles under 14,000 pounds, EPA is proposing a new emissions threshold for monitoring of the diesel particulate filter. The existing requirement for these applications is to detect a catastrophic failure of the device. EPA now believes that a more stringent requirement is appropriate and feasible. The proposed emissions threshold is consistent, both in stringency and in timing, with the proposed particulate matter (PM) thresholds for over 14,000 pound applications.

  • For 2007 and later model year highway heavy-duty diesel vehicles under 14,000 pounds, EPA is proposing a change to the existing emissions thresholds for NOx emissions. The existing thresholds, typically 1.5 times the applicable NOx standard, were established when the engine’s NOx standard was much higher than today’s very low level. EPA believes these OBD thresholds are not technologically feasible in the context of EPA’s very stringent NOx emission standards, and this proposal addresses that issue.

EPA projects that the proposed OBD requirements will result in an increased cost of roughly $50 per diesel engine and $60 per gasoline engine used in applications over 14,000 pounds, and that the proposed new requirements for diesel heavy-duty applications under 14,000 pounds will cost roughly $5 per engine or vehicle.

Additionally, EPA is seeking comment on possible future regulations that would require OBD systems on heavy-duty diesel engines used in nonroad equipment (e.g., construction, industrial, agricultural).




Even if they don't institute specific emissions requirements for off-road vehicles just having the OBD sensors enables a decent capability for monitoring the "health" of an engine. For example: OBD-II can let you monitor injection pulse width, ignition timing, long term and short term fuel trim adjustments, and just about every sensor's output.


Will an expert fill in the missing information?

Is it true that all those huge trucks don't have monitors but cars have used them for a decade?

Granted, diesel is much different and probably the monitoring is tougher. Still it seems idiotic. Trucks rack up huge miles and might be churning out more emissions than 20 cars.

The average car gets tested duuring relicensing. I understand that is a federal mandate.


OBD-II for passenger cars was mandated for cars around model year 1996. This was to standardize the data to make it easier for service technicians to work on any car and also to inact more stringent controls over the emissions equipment.

OBD-I is a terrible mess to deal with (pre 95 cars) as each company developed their own proprietary protocols. Not sure when it was first required.

I don't know what sensors they use on big diesels but they are not required to have OBD...I believe some trucking companies just do thorough maintenance and inspections at a mileage interval that is suitable for them.


OBD-1 appeared in quantities in 1982 on GM cars. In mid-80th it become quite universal, yet every manufacturer have their particular system. Practically all OBD systems up for today have simplified procedure to flush engine trouble codes without scanning tool. One could find specific procedures in Chilton manual, or on-line (extremely useful, highly recommend)

Standard OBD become mandatory in California in 1988. OBD-2 become mandatory in US in 1996, and in Europe in 2001. You can find detailed history in Wiki for “OBD”

Modern OBD-2 interface (quite inexpensive device) could provide real time reading of all of engine/vehicle parameters to laptop or even palm during vehicle operation. It is possible to create GRAPHS of intake air temperature and mass flow, spark advance, air/fuel mixture, fuel consumption, knock sensor data, vehicle acceleration, speed, engine power and torque (the only parameter you have to enter is your tire size), etc. – while you ran quarter-mile or from 0 to 60 mph test. The system is so powerful, it could indicate which exact cylinder misfired couple of times during your two hours drive, or any other intermittent problems.

Unfortunately, repair shops, even at dealerships, still prefer old-time approach and milking the public for unnecessary repairs quite mercifully.

Basic on-board diagnostic is way less challenging than, say, get rid of virus or worm in your computer. Highly recommend to anyone who own post-warranty vehicle.

tom deplume

The only Federal mandate for emissions testing is for noncompliance metro areas. In all my years of vehicle ownership have I ever had to do an emissions test. The current testing protocol is seriously flawed and easily beaten by adding extra oxygenates to the tank just before testing. The whole emissions control program is seriously flawed not just the testing system. Cleaner air will come from changing what goes into the tank not from trying to change what comes out of the tailpipe.


No vehicle out of tune passes emission tests, no matter how much alcohol you add. If your vehicle is properly tuned, works in closed-loop, and have still working cat converter, it will pass. If a little bit of alcohol makes a difference, usually it means that next year you will have to change cat anyway.


I tried testing my OBD computer sensor and it will not even test. I was trying to look up how many wires fit into the back of the my truck theres only four wires in?

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"I tried testing my OBD computer sensor and it will not even test. I was trying to look up how many wires fit into the back of the my truck theres only four wires in?" four wires? but my OBD have no this problem.

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