Failure mode - Duramax 6.6L V8 Turbo Diesel (GM HD, L5P 2017+ generation)

DPF ash loading / excessive regeneration + differential pressure sensor

Reliability tier: verified - verify before ordering, see /disclosure/

Symptoms

regen intervals collapsing from a healthy 400-700 miles to 50-100 miles, with fuel economy dropping to 10-12 mpg highway and constant 'Cleaning Exhaust Filter' messages
'Service Exhaust System' messages and false regen triggers from the differential pressure sensor (codes P2452-P2455)
high EGTs on grades, creeping coolant temps and lost power under tow when the filter restricts

Compare with the other causes of the same sign on this engine: loss of power, limp mode or derate (4 causes) · overheating or temperature creeping up (2 causes) · def, dpf and regeneration warnings (3 causes)

Root cause

Regeneration burns soot but not ash: oil-additive ash and wear metals accumulate in the DOC/DPF/SCR chain (typically 100k-150k miles on an L5P used for towing) until the filter restricts. Separately, the DPF differential pressure sensor and its hoses clog/corrode and trigger false restriction codes - a sensor problem, not a loaded filter.

Diagnosis

track regen intervals over three tanks: under ~200 miles average at 80k+ miles indicates an ash-loaded DPF
differential pressure diagnostics: above ~0.5 psi at warm idle or ~3.0 psi at wide-open throttle under load indicates restriction; pressure should read near zero at key-on/engine-off; replace sensor and hose as a pair
distinguish sensor-fault codes from a genuinely loaded filter before buying hardware

Fixes

replace the differential pressure sensor + hose when codes are sensor-side; replace or professionally clean the DPF assembly when genuinely ash-loaded ()

Prevalence

common