Diesel Aftertreatment Knowledge Base
Evidence-led guides covering system fundamentals, DPF regeneration, SCR and DEF, emissions sensors, component identification and disciplined diagnosis.
SCR System Series · Part 02: Bosch Denoxtronic 2 / 2.1: Airless Dosing, DEF Cooling and Fault Diagnosis
Airless DEF dosing, cooling-return configurations, components, application evidence and diagnostic checks.
SCR System Series · Part 03: Bosch Denoxtronic 2.2: Operation, Components, Applications and Fault Diagnosis
Separate DEF and coolant circuits, catalogue specifications, qualified OE examples and evidence-based diagnosis.
Diesel Aftertreatment System Overview
How DOC, DPF, SCR, sensors and DEF dosing work as one system.
What is a DPF System?
How a diesel particulate filter system works, components and warning signs.
Diesel DPF Regeneration Explained
Passive, active, forced and off-vehicle regeneration — and why regen fails.
How Selective Catalytic Reduction Works
SCR chemistry, DEF/AdBlue and the role of the SCR catalyst.
Common SCR System Faults
NOx sensor, doser, pump and catalyst issues and how to diagnose them.
NOx Sensor: Function, Symptoms and Testing
What a NOx sensor does, upstream vs downstream, failure symptoms and test procedure.
NOx Sensor Failure Symptoms and Checks
Symptoms, upstream vs downstream roles and checks before sensor replacement.
Upstream vs Downstream NOx Sensors
Where each sensor sits around the SCR catalyst, its role and why they are not interchangeable.
Identify an Aftertreatment Part by OE Number
OE number, supersession, position, connector checks and a photo checklist for inquiries.
DPF vs DOC vs SCR
A practical comparison of the three principal aftertreatment stages.
P20EE — SCR Efficiency Below Threshold
What P20EE means, why SCR efficiency drops and how to repair it.
P229F — NOx Sensor Performance
NOx sensor circuit/performance diagnosis and replacement guidance.
P204F — Reductant System Performance
DEF/AdBlue system performance faults, pump/doser diagnosis and repair.
P2BAD — NOx Sensor Circuit Range / Performance
NOx sensor circuit range fault testing and the right BG replacement.