The regens are triggered by a differential pressure sensor on the DPF (besides mileage based regen), and have nothing to do with the temp sensors. On the upstream side, it is seeing full exhaust pressure. On the downstream side, it is seeing whatever density altitude you are in at the time. At high altitudes, with low humidity and high temps, the sensor gets confused because of the density altitude being higher, while the pressure on the upstream of the DPF is the same. It sees this as extreme plugging of the DPF and triggers the "DPF Full - Drive to clean" message. This is why at those same altitudes on a cooler day, or when not towing and creating tons of exhaust flow, you won't see that message. The sensor simply doesn't have enough sensitivity in the atmospheric side. Obviously, the temp sensors come into play when the ECM is monitoring the burn in the system, but are not directly creating the need to drive to clean. Maybe a reflash can correct the sensitivity of the differential pressure sensor.

 

^^^^^^
I think that's the best explanation I've heard so far!

 

Why in the world would it read the Density Altitude, it's a truck not a helicopter? I'm not doubting you are right but it doesn't make sense. Just read the exhaust pressure and clean accordingly. Iam gonna get a flash as soon as I can but I am curious why it would read DA.

 

Density altitude is more or less just what you end up with in a differential pressure transmitter that references ambient pressure as the low side. Had they used just a pressure sensor upstream of the DPF, it would work as you describe. Because it uses a differential pressure transmitter, it takes atmospheric pressure into consideration to find the best guess as to the actual amount of pluggage across the filter.

 

I just got my son an '87 bmw and one of the things about the Bosch motronic 1.0 is that it seeks input from an altimeter in the intake. Fuel mapping to a precise degree has to know barometric pressure which is a function of weather and altitude. Flow restriction would seek the same info I would think, if they want precision and reliability, with accuracy. Gotta have an accurate baseline air density value somehow.

 

I think I have a decent understanding now of the "DPF Full" (real bad), and "Cleaning Exhaust Filter" (normal) messages. The question I have is if you catch the "Cleaning Exhaust Filter" message when it flashes, how long does that cleaning normally take? Like how long do I need to drive to make sure the regen cycle is complete? I haven't purchased the ForeScan app yet, will that tell me when it's 100% clean and the regen is done? Is it like 20 minutes?

 

Mine run 15-30 miles.

 

And you don't *have* to have the app to know. If you just watch your MPG screen, when regen kicks in, your instant MPG drops considerably. when done, it jumps back up again.

 

I keep an eye on the boost gauge. When it's in a regen it spools quicker and usually holds around 9-10psi with a steady throttle. When regen is complete it won't spool much maybe 2-3psi.

 

my regens are about 10 miles in length.

 

Lucky you! I have to go on a 20 mile joy ride to complete a regen. Are you loaded or unloaded in those ten miles?

 

unloaded. I rarely if ever regen loaded. my soot stays at zero to 10% when towing. But when I unhook it will regen but just a short one.

 

My 2008 and 2011 took 10 minutes . my 2015 is 20 to 35 minutes loaded or not, regardless of speed. I lock out 6th, and sometimes 5th to keep rpms up.

 

Thanks guys - great info - I'll give both the MPG and Boost Gauge a peek next time I see the message

 

I watch my regens on my iDash...usually takes 12 to 15 miles, regular driving (60% highway/40% city to work normally), no towing and about 11.3k miles...