Cummins ISX15 DPF and Regen Problems

Read the aftertreatment picture together

Pull soot load, ash load, delta pressure, DOC inlet and outlet temperature, and regen history in one snapshot. Regens closer together over time with soot load resetting each cycle means high soot production upstream. Regens completing but delta pressure staying high means ash or a restriction that regen cannot burn.

EGR and VGT come first on this engine

A leaking EGR valve or a fouled cooler drives soot production up and puts the filter in a constant catch-up cycle. Check EGR differential pressure and valve position against command, and inspect the cooler for internal leakage — coolant in the exhaust stream poisons the DOC and the SCR both. Then verify the VGT actuator reaches its commanded position through the full sweep; a sticking turbo throws exhaust temperature control off and regens suffer.

Delta pressure plumbing

The delta pressure lines on the ISX15 soot up and crack. Remove and clear both lines, verify the sensor reads near zero with both ports open to atmosphere, and inspect the fittings at the filter. Plenty of filters have been replaced over a plugged pressure line.

Injectors and the oil dilution path

One injector with an excessive return or a bad spray pattern will load a filter quickly and put fuel in the oil. Check the return flow across all six and look at the oil level trend — a rising oil level means fuel dilution, and that ash-loads the filter early as well as damaging bearings.

Before you buy a filter

• Confirm ash load, not soot load, is what is high.
• Rule out a stuck-open thermostat blocking regen enable.
• Verify all exhaust temperature sensors agree at a cold soak.
• Check for exhaust leaks at the DOC inlet and between modules.
• Confirm no coolant loss — a leaking EGR cooler ruins the new filter too.