Failure mode - Cummins 6.7L ISB (Ram HD)

Holset VGT turbo sticking / actuator failure

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

Symptoms

loss of exhaust-brake function (the classic first sign - the VGT is the exhaust brake)
low power / boost DTCs (over/underboost), smoky acceleration
turbo actuator DTCs; 'Service Electronic Throttle'?
excessive idle/lope or whistle change; failed regens because the turbo cannot build regen heat

Root cause

The electronically-actuated Holset variable-geometry turbo (HE351VE 2007.5-2012 pickups, HE300VG 2013+ pickups) moves its nozzle vanes for boost control, exhaust braking and DPF regen heat. Soot from regens and EGR fouls the vanes/unison ring; the electric actuator is exposed to heat and fails independently. Wikipedia's B-Series article calls the VGT 'an extremely common issue' typically flagged by exhaust-brake loss.

Diagnosis

actuator/nozzle-position DTCs and live vane-position PID vs commanded - stuck or lagging vane position is the tell
test the exhaust brake at cold start: no RPM dip / braking effect = nozzle not closing
inspect vane motion with the actuator commanded (shop tool); look for soot coke in the turbine housing
rule out boost leaks (boots, CAC) before condemning the turbo

Fixes

replace the electronic actuator alone when vanes move freely but the actuator is dead (cheaper than a turbo) ()

vgt-actuator (part category - specific model not chosen)

reman/upgrade turbo (HE351VE-family reman or bolt-on upgrade; 2013+ HE300VG unit) ()

vgt-turbo (part category - specific model not chosen)

address the soot source: duty cycle / regen health and EGR condition, or the replacement turbo will coke too ()

egr-valve (part category - specific model not chosen)

Prevalence

very-common