Incomplete Regen — Fuel Dosing / Hydrocarbon Injection Path
Incomplete regen caused by fuel dosing problems is diagnosed by reviewing the abort reason, monitoring HC command and temperature rise, and verifying the doser circuit and DOC condition.
Fault Overview
Incomplete or aborted regeneration caused by insufficient hydrocarbon (fuel) dosing to the DOC, preventing proper DOC light-off and DPF temperature rise. Applies to systems using in-cylinder post-injection or a separate hydrocarbon doser/7th injector to raise DOC/DPF temperatures during active regen.
Engine & Platform Coverage
Symptoms
- •Incomplete regen
- •Regen abort fuel dosing
- •HC dosing fault
- •Hydrocarbon injector
- •7th injector
- •Regen fuel injection
- •DOC light-off failure
Possible Causes
- 1.Failed or restricted hydrocarbon dosing injector
- 2.Low fuel rail pressure during regen
- 3.Wiring or driver circuit faults on the doser
- 4.Incorrect injector calibration
- 5.Exhaust leaks before the DOC
- 6.DOC face-plugging preventing light-off
- 7.Temperature sensor errors aborting the event
- 8.EGR or boost issues affecting oxygen for combustion of the dosed fuel
Wiring & Circuit Notes
Inspect the HC doser or post-injection circuit for open, short, or high-resistance conditions. Check connectors for heat damage and fuel contamination.
DVOM Specs & Sensor Tests
Commanded HC dosing quantity or pulse width during regen. Rail pressure stability. DOC inlet and outlet temperature rise rate. DPF inlet temperature target achievement. Doser circuit resistance and current. Exhaust oxygen or lambda if available.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
6 steps locked behind Technician Mode- 1Step 1 — Retrieve the Specific Regen Abort Reason from the ECM: Retrieve the specific regen abort reason from the ECM. HC doser restriction from coking or contamination is common. Many platforms log specific abort reasons related to temperature rise rate.
- 2Step 2 — Monitor Commanded HC Dosing, Rail Pressure, and DOC/DPF Temperatures During Forced Regen: Monitor commanded HC dosing, rail pressure, and DOC/DPF temperatures during a forced regen. Exhaust leaks before the DOC and DOC face-plugging are frequent non-dosing causes of failed light-off.
- 3Step 3 — Verify the Doser Circuit Electrically: Verify the doser circuit electrically (resistance, voltage, current). Inspect the HC doser or post-injection circuit for open, short, or high-resistance conditions.
- 4Step 4 — Check for Exhaust Leaks Upstream of the DOC: Check for exhaust leaks upstream of the DOC. Even moderate leaks prevent the DOC from reaching light-off temperature.
- 5Step 5 — Evaluate DOC Face Condition if Temperatures Fail to Rise: Evaluate DOC face condition if temperatures fail to rise despite confirmed HC dosing.
- 6Step 6 — Confirm Fuel Quality and Rail Pressure Under Regen Load: Confirm fuel quality and rail pressure under regen load. Low rail pressure during the high-demand regen event is a common finding.
- 7Step 7 — Repair the Dosing Circuit or Restriction, Then Retest a Complete Regen: Repair the dosing circuit or restriction, then retest a complete regen to confirm temperature targets are met.
Unlock the full evidence-gated diagnostic sequence, DVOM test steps, and repair procedures in Technician Mode.
Full Diagnostic Access
Verification steps, preventative measures, severity guidance, and legacy comparison are available in Technician Mode.
Typical Repair Costs
Clean or replace HC doser $200–600; repair circuit $100–300; repair exhaust leak $100–400; clean or replace face-plugged DOC $300–2,500; correct rail pressure issues variable.
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Related Systems
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Related Sensor Locations
Common Symptoms
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Summary
Use the AI Diesel Tech diagnostic engine to run this code through a structured, evidence-gated sequence and get a confirmed root cause before any parts are replaced.