Diesel Oxidising Catalyst (DOC)


Diesel Oxidisation Catalyst

The Diesel oxidation catalyst (DOC) is the first device in the aftertreatment system in the exhaust system. DOC is a catalytic converter designed specifically for diesel engines to reduce Carbon Monoxide (CO), Hydrocarbons (HC) and Particulate Matter (PM) emissions. DOC's are simple, inexpensive and suitable for all types and applications of diesel engines.

How Diesel Oxidising Catalyst (DOC) Works

Modern catalytic converters are made of a monolith honeycomb substrate coated with platinum group metal catalyst, packaged in a stainless-steel container. The honeycomb structure with many small parallel channels presents a high catalytic contact area to exhaust gasses. As the hot gases contact the catalyst, several exhaust pollutants are converted into harmless substances such as carbon dioxide and water.

The diesel oxidation catalyst is designed to oxidize carbon monoxide, gas phase hydrocarbons, and the soluble organic fraction (SOF) of diesel particulate matter to CO2 and H2O. Both the DOC and the DPF are honeycomb ceramic filters.


As an owner/driver of a Diesel-powered vehicle you need to clean the DOC regularly as this will save you money in operating costs and prevent costly downtime in the long run.

Maintenance schedules or cleaning cycles vary according to the type of vehicle and how your vehicle is being used.

To keep your DOC’s optimal operating performance, we suggest a clean at least every 12 months in conjunction with your DPF. Shorter timeframes may be needed if your vehicle is exposed to peak hour traffic at low speeds, short stop/start trips or extended periods where engine is at idle.

DOC’s do not become blocked like a DPF does because they aren’t catching particulates but more so are converting carbon monoxide (CO) and hydrocarbons into carbon dioxide (CO2) and water. It may have an accumulation of deposits on the catalyst’s internal construction over time which Exhaust Clean Australia can remove using our patented machine from Italy which will restore it to as new condition!

  • Poor fuel consumption
  • Noticeable decline in performance
  • Increase in smoke from exhaust system
  • Vehicle goes into limp mode with a fault code relating to DOC
  • If your vehicle has had a failure with fuel injectors, turbo, head gasket, high oil consumption, EGR system malfunction/failure

Exhaust Clean Australia has the fastest turnaround time on the market due to our revolutionary “Flash Clean” technology.

From as little as 3 hours to same day service with free pickup and delivery in the Brisbane metropolitan area.

If your DOC has been subject to oil or coolant contamination due to an engine component failure allow extra time for an additional step in the cleaning process to return your DOC back to its original state.

Exhaust Clean Australia offer warranty on all our workmanship where the vehicle is operated according to manufacturer’s specification

From as little as $ TBC. Compare that the cost of a replacement DOC that could set you back anywhere from $ 1000 - $ 8000. Cleaning your DPF is a very cheap cost alternative for your vehicle.

Pricing structure here:

  • Diesel particulate filters – from $450 + gst
  • Cat Convertors – from $340 + gst
  • Diesel oxidising catalysts – from $340 + gst
  • Selective catalyst reductors – from $390 + gst
  • Intercoolers – from $110 + gst
  • Exhaust gas recirculation – from $100 + gst

There are some chemical products on the market that claim to be able to clean blocked DOC’s but do not achieve anywhere near the results we are able to at Exhaust Clean Australia with our revolutionary Italian made technology

To help prevent your DOC from becoming contaminated ensure that the vehicle’s service schedule is adhered to and correct engine oil is used. Preventative maintenance is better than reactive maintenance!! Find an independent mechanic that is familiar with your make and model of vehicle and is experienced in servicing modern diesels. This will ensure that they have a thorough knowledge of your vehicle and that they know all the tips and tricks in fault finding any problems.

DOC systems are very technical, and some mechanics may not fully understand their complex operation, and in our experience, that also includes some dealerships. Some workshops may use the “keep replacing parts” method hoping it’ll solve the fault, but inevitably your bank balance will cop a hiding! Try to find a diesel specialist workshop that frequently deal with DOC systems and understand how they work. They’ll be able to pinpoint the cause of the fault and replace or repair only the parts that are necessary. Once the fault has been rectified, your mechanic can send the DOC to Exhaust Clean Australia to be returned to an “as new” state!

No, it’s illegal to remove or delete your DOC. Your vehicle has been designed by the manufacturer to operate with a DOC system. It is illegal and will also void the manufacturer’s warranty on your vehicle and Australian consumer law protections. Removal or deletion of your DOC will also impact your vehicle’s insurance policy.

DOC’s are fitted to enable the vehicle to comply with the Australian Design Rules (ADR) emission requirement levels.

The relevant ADR for light vehicles is ADR79/01

The relevant ADR for heavy vehicles is ADR80/01

It is illegal to operate a vehicle that does not meet the ADR requirements so removing or deleting a DOC will result in non-compliance with all relevant emissions ADR’s.

In addition to commonwealth legislation, each state and territory also have additional legislation that require DOC’s to be fitted and operated in accordance with manufacturer requirements.

Our Partners


manufacturer/type of vehicle