The diesel oxidation catalyst (DOC) sits ahead of the particulate filter and helps burn off pollutants and generate the heat needed for regeneration.
What it does
The DOC oxidizes carbon monoxide, hydrocarbons, and injected fuel during regeneration, raising exhaust temperature so the downstream DPF can burn off its trapped soot. A healthy DOC is essential for the whole aftertreatment to work.
Signs it is failing
- Poor or incomplete regeneration
- Aftertreatment and temperature fault codes
- Reduced efficiency of the DPF
- Possible derate in severe cases
Replacement and what to know
A degraded or contaminated DOC is replaced, and the upstream causes such as excessive oil or fuel contamination are addressed. Because the DOC and DPF work together, a problem in one often shows up as symptoms in the other.
Frequently asked questions
What does a DOC do?
It oxidizes pollutants and raises exhaust temperature during regeneration so the DPF can burn off its soot.
How is it different from the DPF?
The DOC oxidizes gases and creates heat; the DPF physically traps soot. They work together in the aftertreatment.
What harms a DOC?
Excess oil or fuel contamination from upstream problems can degrade it, so address those causes.
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