EPA-420-F-10-030

 May 2010

National Clean Diesel Campaign

www.epa.gov/cleandiesel

Diesel Oxidation Catalyst

Installation, Operation, and Maintenance

Technical Bulletin

Pre-Installation 

Prior to installing any retrofit device, it is important 

to perform a thorough engine inspection and review 

maintenance records to ensure proper engine operation. 

Vehicles with excessive fuel or lubrication oil consumption 

should be repaired prior to installing retrofit technologies. 

Excessive blowby emissions can be a sign of engine wear 

and further inspection of the engine may be necessary. 

Prior to installing a retrofit, the exhaust system integrity 

should also be confirmed. 

Technology Selection 

To select the best Diesel Oxidation Catalyst (DOC) for a 

specific vehicle, it is necessary to identify: 

• Vehicle Type: Highway or Nonroad

• Vehicle Class: School Bus, Class 8A Tractor, Ferry, 

Locomotive, Forklift, etc

• Vehicle Specifications: Manufacturer, Model, Model Year 

• Engine Specifications: Manufacturer, Model, Model Year, 

Displacement, Horsepower, Engine Location on Vehicle, 

Turbo-charge, Exhaust Gas Recirculation (EGR)

• EPA Engine Family Name: Can be found on the engine’s 

emission label and contains 12 or 13 characters such as 

TCP7.2RZBDBRB or 3NVXHO466ANA

• Annual Miles Traveled (Highway) or Annual Hours of 

Operation (Nonroad)

• Engine-out PM emission levels 

• Any unique vehicle, equipment or engine operation that 

may create unusual conditions on the exhaust system or 

DOC. Conditions such as high vibration or shock loading 

may warrant special consideration in DOC selection and/or 

mounting. 

The United States Environmental Protection Agency (EPA) 

and the California Air Resources Board (CARB) maintain 

lists of verified diesel retrofit technologies that define the 

specific applications and engine operating criteria that 

must be met to successfully apply a particular retrofit 

technology (www.epa.gov/otaq/retrofit/verif-list.htm). 

When installed as described on the verified technologies 

list and within the verified scope of coverage, a device 

is expected to achieve the verified performance and 

durability. 

Exhaust Temperature Data Logging 

To achieve verified levels of emissions reductions DOCs 

typically require a minimum exhaust gas temperature of 

150°C. This temperature requirement is met in normal 

operation with most duty cycles. Data logging is not 

typically necessary to evaluate acceptable exhaust gas 

temperatures prior to DOC installation.

Installation 

Installation may be performed by the retrofit supplier, or 

the retrofit supplier may provide training to fleet personnel 

to perform installation. 

In most applications, the DOC may be configured to 

match the dimensions of the conventional muffler and 

can be installed as a muffler replacement. In other cases 

the space available for DOC installation on the vehicle or 

equipment is very restricted and the DOC configuration 

must be custom-designed. Safety, visibility, and vibration 

issues may also need to be addressed by a custom 

Diesel Oxidation Catalyst (DOC) 

on Track Dozer
installation. The time required for DOC installation will vary 

depending on the situation and is generally one to three 

hours. 

Since a DOC typically weighs more and may be larger than 

the muffler, stronger clamps and brackets are required in 

place of those used with the original muffler. Failure to utilize 

appropriate hardware and follow mounting instructions can 

result in a failure of support brackets and damage to the 

equipment or vehicle. 

The DOC must be mounted within a set distance of the 

exhaust manifold, as specified by the manufacturer. While 

not normally necessary, exhaust pipe insulation may 

be used to retain heat when the DOC is mounted a long 

distance from the turbo charger. 

Documentation should remain with the vehicle and/or in 

fleet records which lists installation and vehicle information 

such as mileage, date, device model number, installer, etc. 

Operation and Maintenance 

Once properly installed, DOCs require little maintenance. 

DOC manufacturers and product suppliers should provide 

vehicle service technicians with training on proper 

retrofit maintenance procedures. Periodic inspection and 

tightening of mounting hardware is typically appropriate.

Plugging is very rare, but it can occur in older, high-emitting 

or poorly maintained vehicles and/or if an engine has a 

mechanical failure. Long duration idling should also be 

avoided. If a DOC is overwhelmed with unburned fuel 

or lubricants (ash) it may need to be cleaned and the 

manufacturer’s instructions should be followed. 

It is important to properly maintain vehicles and monitor 

fuel and lubrication oil consumption. A bad fuel injector or 

increased oil consumption may be masked by a DOC. The 

DOC may be damaged by excessive fuel or oil consumption 

or a poorly maintained engine.