OBD-II (On-Board Diagnostics, Generation II) mandates that every ECU must run standardised self-test functions for emissions-relevant systems. These tests are called "readiness monitors" — they verify whether the relevant system is functioning correctly and display the result as "Complete" (finished, no fault) or "Incomplete" (not yet run).
Monitors are reset to "Incomplete" after every battery disconnect or fault memory clear. Specific driving conditions (drive cycles) must then be met for each monitor to complete its test.
Continuous monitors (always running):
Misfire monitor: detects misfires via crankshaft irregularity. Fuel system monitor: verifies lambda control is working correctly (LTFT/STFT within limits). Component monitor: checks whether all sensors deliver plausible signals.
Non-continuous monitors (require specific driving conditions):
Catalyst monitor (CAT): compares lambda sensor before and after catalyst — detects ageing. O2 sensor monitor: checks response time and amplitude of lambda sensors. EGR monitor: verifies EGR valve position is plausible. DPF monitor: monitors differential pressure and regeneration cycles. EVAP monitor (petrol): checks fuel vapour retention system for leaks.
After a standard Stage 1 remap, all monitors remain active — a clean remap does not disable any OBD monitors. After a complete drive cycle all monitors should show "Complete" again.
After a DPF-Off or EGR-Off, the corresponding monitors are deactivated as part of the software solution. A professional DPF-Off deactivates the DPF monitor, part of the EGR monitor, and all associated DTC monitors — but leaves all other monitors (misfire, fuel system, catalyst) intact.
At periodic vehicle inspections, modern test lanes read the OBD system. Checked are: whether active fault codes (DTCs) are present, and whether the readiness monitors show "Complete". In Austria (§57a KFG) and Germany (HU), too many "Incomplete" monitors result in a re-inspection — even without active fault codes.
Specifically: in Germany, vehicles from Euro 4 onwards may have at most 1 monitor Incomplete (for vehicles up to 2000: at most 2). Austria applies similar thresholds depending on the test centre. A clean DPF-Off from ecufiles.io accounts for exactly these limits — only the DPF monitor is deactivated, all others remain fully functional.
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