DD13 SPN 3251fmi 21

[Therealarw]

(11-13-2025 )mikkhh Wrote:  Just my experience. Differential pressure faults on those have been problem with the aftertreatment control unit itself. Not wiring or sensor issue. Sensor values are drifting also as they age, but even old sensors are not giving pressure not plausible. Getting more and more common as they age. Then somebody throws somekind of deman emulator or does somekind of crappy elimination of those systems, but edits aftertreatment module instead of using factory solution to deman them that involves throwing away both cans and their control unit + coding the truck so it will not cry about missing modules. After some time there is no communications on a c m so then all of that crappy deman goes to waste or they have old control unit fixed that would have cured all their problems in the first place.

How much new control unit costs? Used ones are lottery too and cost like a grand? At least in my area. Those engines are on benz trucks here, some forestry equipment and combine harvesters in agriculture. You need to find matching hardware control unit (some revision that starts with D...) and have somebody clone the software over OR have somebody fix the old one who knows what they are doing. Although engine control unit looks the same, they are not internally same and are not compatible.

So far the repairs have been succesful and and it costs like a grand to fix them, but we are in Europe and if NEW CONTROL UNIT is tolerable price just buy new one. Most guys "fixing" them are complete cowboys and will cause more harm than good. I would opt to repair them if trucks operate locally and even if repairs fail there is no huge tow bill coming.

Yea man, I looked at all the sensors everything looked clean, i wouldn’t be too concerned if the truck was local and did local jobs but this one runs about 4-700 miles a day. It runs fine no loss of power it just keeps coming on, I’ve looked at everything on it. These freight liners have so many modules it could be anything