Aftertreatment Restriction Decision Tree — DOC + DPF
Use the aftertreatment restriction decision tree on every high-DP or power-loss complaint before removing the DPF or DOC.
Fault Overview
System decision tree for progressive restriction diagnosis covering both DOC and DPF, from sensor and hose checks through ash, soot, face-plugging, and internal damage. Most restriction complaints are resolved at the sensor-hose, soot, or ash step without component replacement.
Engine & Platform Coverage
Symptoms
- •Aftertreatment restriction tree
- •DOC DPF restriction diagnosis
- •High backpressure decision
- •Progressive restriction path
Possible Causes
- 1.DP sensor hose restriction (most common)
- 2.Soot load from failed regens
- 3.Ash accumulation
- 4.DOC face-plugging
- 5.Exhaust leaks skewing readings
- 6.Oil/coolant contamination
- 7.Internal DPF damage
Wiring & Circuit Notes
DP and temperature sensor circuits are verified at the appropriate steps in the tree.
DVOM Specs & Sensor Tests
DP at idle and load. Pre- and post-regen DP. Full temperature map. Abort reasons. Visual/borescope results.
Diagnostic Flow — FSM Sequence
AI Diesel Tech enforces this evidence-gate sequence. Each gate must pass before advancing.
7 steps locked behind Technician Mode- 1Step 1 — Verify DP Sensor Hoses and Ports Are Clean and Connected: Verify DP sensor hoses and ports are clean and connected. Clogged tubes are the most common cause of false high-DP complaints.
- 2Step 2 — Confirm Temperature Sensors Are Rational: Confirm temperature sensors are rational. Faulty sensors can mask or mimic restriction.
- 3Step 3 — Perform a Complete Regen and Compare Pre/Post DP: Perform a complete regen and compare pre/post DP (soot vs ash). This is the definitive soot/ash differentiation test.
- 4Step 4 — Review Regen Abort History and Correct Any Abort Causes: Review regen abort history and correct any abort causes. A system that cannot complete regens will always show high soot load.
- 5Step 5 — Evaluate DOC Face Condition if Light-Off or Upstream Restriction Is Suspected: Evaluate DOC face condition if light-off or upstream restriction is suspected.
- 6Step 6 — Check for Exhaust Leaks That Skew Readings: Check for exhaust leaks that skew readings.
- 7Step 7 — Inspect for Oil/Coolant Contamination Sources: Inspect for oil/coolant contamination sources.
- 8Step 8 — Clean Ash or Replace Damaged DOC/DPF Only After the Above Steps: Clean ash or replace damaged DOC/DPF only after the above steps. Correct engine-out soot or oil consumption as needed.
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
Directed by the tree — hose service, successful regen, ash cleaning, DOC service, or DPF replacement with root-cause correction.
Start Diagnosing This Fault Now
AI Diesel Tech walks you through every evidence gate in the correct order. Choose the plan that fits your shop.
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AI Diesel Tech — The Technician's Diagnostic Engine
AI Diesel Tech diagnostic logic is built by an ASE Certified Diesel Technician and engineered for professional shop use. Trusted by technicians nationwide — used in shops, fleets, and training programs.
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.