g/auto • Posted by u/diesel_dan • 1 days ago

Regen not completing on a 2021 Peterbilt 579 — DPF issue or active regen inhibit?

Fleet Peterbilt 579 with Paccar MX-13. DPF light came on, driver attempted active regen per the procedure. Regen starts and runs for about 8 minutes then aborts with a "Regen Failed" message.

No fault codes pulling active. Aftertreatment inlet temp gets to 1,050°F before the abort. EGR and DOC look normal.

I'm thinking either a plugged DPF (but ash only, soot load should be low based on mileage), or there's an inhibit condition the diagnostic isn't showing. Any starting points?

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u/scan_tool_sam • 1 days ago

On the Paccar MX-13, there's a known inhibit from coolant temperature — if the engine is getting hot during the regen cycle (common in summer or on trucks without good airflow at idle), the ECU aborts regen to protect the engine. Check coolant temp during the regen. If it's climbing above 210°F, that's your abort trigger.

u/wrench_monkey • 1 days ago

Check your DPF differential pressure sensor reading against spec. A partially plugged DPF will show normal soot levels on a relearned sensor but the actual restriction is ash buildup — INSITE won't always flag ash as a problem since it doesn't burn off like soot. Also check the DPF pressure sensors themselves — they fail and can cause premature regen aborts.

u/diesel_dan OP • 1 days ago

Update from after posting: Pulled the DPF and took it to a cleaning service. It was at 95% ash loading. Cleaned it, reinstalled, regen completed perfectly. Mileage was way off because the previous shop reset the soot sensor without resetting ash life. Always check ash life separately from soot load.