A truck is losing coolant with no external leaks, and white steam with a sweet smell comes from the exhaust. The oil is clean. Which component is the most likely cause?
- A leaking charge air cooler
- A leaking EGR cooler
- A stuck wastegate actuator
- A plugged fuel-water separator
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B. A leaking EGR cooler
The EGR cooler passes exhaust gas through a coolant-filled core; when the core cracks, coolant enters the gas stream and leaves as steam. A charge air cooler carries only air, so it cannot lose coolant.
Reference: ASE T2 Diesel Engines task list, exhaust aftertreatment (EGR cooler diagnosis)
During an active regeneration, what is the job of the diesel oxidation catalyst (DOC)?
- It converts oxides of nitrogen into nitrogen and water
- It stores soot until the exhaust is hot enough to burn it
- It oxidizes the dosed fuel to heat the exhaust for the DPF
- It turns diesel exhaust fluid into ammonia for the SCR catalyst
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C. It oxidizes the dosed fuel to heat the exhaust for the DPF
Fuel added by a doser or late injection burns across the DOC without a flame, raising exhaust temperature to roughly 1,000 to 1,200 degrees F so the soot in the DPF burns. Converting NOx is the job of the SCR catalyst.
Reference: ASE T2 Diesel Engines task list, exhaust aftertreatment (DOC and DPF regeneration)
What is passive regeneration of a DPF?
- The control module doses extra fuel to raise exhaust temperature
- Soot burns off during normal driving when exhaust heat is high enough
- The technician starts a parked regeneration with a scan tool
- The filter is removed and cleaned off the truck in a pneumatic cleaning machine
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B. Soot burns off during normal driving when exhaust heat is high enough
Under sustained load the exhaust is hot enough, with help from the catalyst, to oxidize soot continuously without any added fuel or driver action. Dosing extra fuel is what makes a regeneration active.
Reference: ASE T2 Diesel Engines task list, exhaust aftertreatment (DPF regeneration)