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Dealing with diesel emissions

Learn how to properly maintain the growing number of modern diesel engines on the road.
Tuesday, November 1, 2016 - 06:00
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Not so long ago testing diesel emissions meant simply looking at the exhaust coming out of the tailpipe and making sure it didn’t look too bad.

Times have changed.

Emission standards for diesel-powered vehicles have become very strict and complying with these strict emission rules, while still producing a powerful and responsive vehicle, is definitely no easy task for manufacturers. Balancing power and emission control is critical though, so some new diagnostic strategies were developed and are now widely (and successfully) used to keep newer diesel-engine emissions down at the levels where they need to be. And it’s well worth learning about these diesel emission management systems since they’re so widely used and diesel vehicles are indeed gaining in popularity.

Some diesel emission management strategies are fairly simple – like reintroducing EGR valves to reduce NOx emissions.

Some strategies, however, are quite complicated and tamper-resistant, such as installing diesel particulate filters (DPF) and selective catalytic reduction (SCR) systems that use diesel emission fluid (DEF) on newer vehicles – systems that do work well, but unfortunately can cause real headaches if you’re not sure what you’re dealing with or if you don’t know what to expect during service.

Vehicles that spend much of their time idling or driving at low speeds may need the DPFs replaced more frequently than ones that do highway driving.

Complicating matters further, many newer diesel vehicles will go into “limp” or “idle-only” mode (derating the engine so that the vehicle can only be driven at very low speeds until the emission-related fault is fixed) when a problem in the emission system is detected – and it may take time and patience to reset the emission systems back to normal operation afterwards since fixing the problem is not always as simple as it would seem.

In other words, even if the only thing you have to do with diesel-powered vehicles is the occasional oil change, it’s still important to understand the basics of how diesel emissions are managed so that you don’t inadvertently cause problems for your customers, or waste time doing things that won’t repair problems effectively because mistakes can be both time consuming and costly.

Common problems with diesel emission systems
  • SCR / DPF clogged (Typical fix is regeneration, resetting parameters – or replacing the component)
  • Tank heater fails / tank and pump cracked (Typical fix is replacing the component)
  • Contaminated DEF (Typical fix is testing and replacing the DEF)
  • Programming updates (Typical fix is performing updates as required)
  • Running out of fluid (Fixes vary, typically topping up fluid and performing regeneration if required)
  • Stuck in Idle-only mode (Typical fix is correcting the cause and performing regeneration)
  • Won’t go into regeneration mode (Typical fix is correcting the problem in the underlying system and checking for calibration updates)

But don’t worry. Dealing with diesel emission systems is actually manageable and even profitable with a bit of background knowledge and a few hard-earned tips to fall back on.

Here’s how.

Dealing with DPFs

Diesel-engine exhaust emissions, unlike gasoline-engine exhaust emissions, must have the particulate matter (“soot”) removed, which is commonly done by filtering it out with a diesel particulate filter (DPF).

Always consult service information for specific details about the vehicle you’re working on (as with any vehicle system), but in very general terms diesel particulate filters are located inside the exhaust system, much as catalytic converters are, and work by forcing exhaust gas to pass through a substrate that traps the unwanted particles while allowing the gas to pass on through.

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