Failure mode - Cummins 5.9L Diesel (Dodge Ram HD)

Intake grid heater / relay failures (cold starts)

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

Symptoms

long crank and white smoke in cold weather; 'wait to start' behaviour that ignores temperature
in severe cases: melted grid heater elements or welded relay contacts, battery drain

Compare with the other causes of the same sign on this engine: hard start, long crank or no-start (4 causes) · white smoke from the exhaust (2 causes)

Root cause

The 24v/CR engines light off via an intake grid heater fed by high-current relays; corroded high-current connections and worn relays break the heat cycle. A failing heater also soots the intake (the later 'grid heater bolt' story on the 6.7 is the same hardware family).

Diagnosis

verify relay operation and voltage drop across the high-current studs at key-on
check for intake sooting and loose grid-heater plate bolts (air leak into the intake)

Fixes

replace relays/repair the high-current circuit; reseal or replace the grid heater assembly ()

5.9L Cummins Billet Grid Heater Replacement (1/2-inch taller)

Prevalence

occasional