While the DPF and DOC are the components we typically associate with aftertreatment service issues, improperly maintained aftertreatment systems can lead to a host of other operational issues.

“Issues with the emissions system can have a ‘knock-on’ effect on various components in the engine environment,” said Dr. Barry Southward, vice president of catalyst technology for AP Emissions. “For example, the efficiency of fuel injectors may be affected. This is turn can set up yet another negative feedback loop since atypical fuel injection from partial blocked injectors can both increase the rate of soot production, due to non-homogeneous air-fuel mixing, but can also compromise HC post-injection.

“This in turn results in affects the ability of the DOC to initiate the thermal response required for active DPF regeneration,” Southward continued. “In addition, heterogeneous fuel injection into the DOC can give rise to ‘face-plugging’ i.e. channel blockage of the DOC which, under conditions of low load and low speed engine operation, further restrict flow through the DOC and DPF, and again result in power losses and decreased fuel economy as well as potential increases in emissions.”

Exhaust gas recirculation plugging can also occur.

“A bad aftertreatment system can impact the engine’s performance due to high back pressure which can affect the combustion performance and air-to-fuel ratio, which can in turn lead to excessive soot and HC buildups which can plug the EGR cooler,” said Darren Gosbee, vice president of engineering for Navistar Inc.

“The net result of the turbocharger operating outside normal temperature and flow conditions are decreased turbo efficiency (engine power), increased prevalence and severity of oil leaks, carbonization of oil within the turbo, which can unbalance or other compromise the integrity of the turbo, e.g. by soot deposition on the turbo vanes, as well as exhaust gas leaks from the turbo,” Southward said. “Indeed, there are many documented cases of turbine wheel failure, due to excess temperature, as well as turbo failure arising from complications associated with carbon build-up within the entire turbo assembly. A further concern may arise if the engine in question employs a variable-geometry turbocharger [VGT], as the soot can directly damage the VGT actuator causing problems for the effective operation of the unit.”

“Issues with the emissions system can have a ‘knock-on’ effect on various components in the engine environment.”
— Dr. Barry Southward, AP Emissions

Gosbee went on to rattle off several other consequences: oil contamination, out-of-compliance emissions at the tail pipe and sensor failure.

“Ignoring aftertreatment maintenance can lead to MIL and inducement derate, as well as failure to comply with emission requirements,” he stressed. “And all sensors related to aftertreatment components, such as DOCs, DPFs, SCR, ammonia slip catalyst (ASC), temperature sensors, exhaust gas temperature, PM, NOx and delta_P, are more prone to failure if aftertreatment-related issues and fault codes are ignored.”