Begin with plausibility
With the engine stopped, differential pressure should be evaluated against the manufacturer procedure and sensor specification. An offset, an implausible jump or a fixed reading can indicate a sensor, hose, wiring or reference problem rather than filter restriction.
Under controlled engine speed or load, compare pressure behavior with airflow and temperature. A single universal pressure threshold is not appropriate across filter sizes and vehicles.
Inspect the complete system
Check hoses for splitting, blockage, condensation, incorrect routing and heat damage. Review exhaust temperature sensors because regeneration control depends on credible temperature information.
Excess soot can be the result of injector, boost, EGR, air-leak, thermostat or driving-pattern problems. Replacing or cleaning the filter without resolving the cause can produce a repeat failure.
Legal and workshop boundary
For road vehicles, emissions equipment must remain compliant with the rules that apply in the vehicle's market. The correct workflow is diagnosis, approved repair or replacement, and verification.
Calibration work must never be presented as a substitute for diagnosing a mechanical or sensor fault. Record the pre-repair codes, measurements, corrective action and post-repair result.