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From the tech folder:
P2002 REGEN Particulate Trap Efficiency
Below Threshold
This error occurs if an expected pressure drop through the DPF
is lower than the specified value following a regeneration cycle
(based on the concept of normalized pressure differential
but like I said, aftermarket intakes seem to throw the code. So if you have an aftermarket one on there...take it off and see.
aftermarket intake is the cause. Ive stated this more then once.
the maf is the part of the dpf load calc. they take that and dpfe and that is what causes the code.
so incorrect air flow, dirty maf sensor dirt air filter will cause this.
also it is possible to enter excessive regen based on the same wich will reduce fuel economy and incress speed of oil growth.