Two Exhaust Regens Are Better than One
Getting all that nasty soot and exhaust contamination out of the exhaust system DPF (diesel particulate filter) takes time and heat to do a proper job. The first step to take is to do a ‘parked regen’ where the diagnostic software comes in handy to force it to happen.
The regen switch usually found on the dash can be actuated by anyone but if the planets are not aligned for a regen to occur the computer will not allow this to take place. The parameters have to be at a certain level before the on board computer lets the system go into regen mode.
The regen switch on the dash is for the driver or tech to use if the regen alert dash light starts to come on during a trip. The driver must stop when the light starts to flash and do a regen before the engine shuts down. Then you need a tow truck to take your vehicle to the dealer for a reboot of the on board computer system.
We’ve never had this happen in our fleet and it may be attributed to the hills and valleys we drive our buses through. These routes keeps the engine hot and there is not a huge threat of having to do a roadside regen. It has happened because of a programming issue but not because of a plugged up exhaust system.
Starting With a Parked Regen
It was recommended to us by the dealer that getting a proper exhaust regen accomplished requires a ‘parked regen’ and following that an ‘over the road regen’. Obviously the ‘parked regen’ is first before the road trip….so using the diagnostic software we set it all up and let the engine go through the process for approximately 30 minutes.
Over The Road Regen
The ‘over the road regeneration’ procedure requires the laptop where you can just click on this action and then go for a road test. This will get the engine good and hot under load and help with the big soot burn out. The Mercedes uses a doser valve that shoots diesel down the pipe and through the DOC (diesel oxidation catalyst) where it reacts chemically to remove NOx contaminants.
One thing you need is some extra time to carry out this task. Not only can you regen the exhaust system but also monitor the engine. The one parameter you need to watch is the inlet and outlet pressures on the DPF. The maximum allowed pressure differential is 3 psi which determines if the DPF has blockage.
Diagnostic software is the ‘NOW’ tool that any commercial vehicle repair shop or any repair shop for that matter has to have. It would be fruitless to even consider working on today’s vehicles without a laptop and the proper software. I know you are aware of this already if you’re a diesel tech but I had to put this fact out there.