On-Board Diagnostics (OBD-II) is a standardized system that monitors emissions-related components and reports malfunctions. OBD readiness monitors must complete successfully for vehicles to pass emissions inspections.

Visión general

The ECU continuously runs diagnostic monitors for all emissions-relevant systems. When a fault is detected, a DTC is stored and the MIL (check engine light) illuminates. Some monitors require specific driving conditions to complete.

Key Monitors

• Catalyst efficiency
• Oxygen sensor response
• Flujo EGR
• EVAP system integrity
• Misfire detection
• Fuel system
• Secondary air (if equipped)

Readiness Status

• Complete — monitor has run and passed
• Incomplete — monitor has not run yet
• Not applicable — vehicle doesn’t have this system

Logic Overview

Driving Cycle → Enable Conditions Met?
         ↓ YES
Run Diagnostic Monitor
         ↓
Pass → Set Readiness Complete
Fail → Store DTC, Illuminate MIL

Calibration Considerations

• Disabling emissions systems sets readiness to “not ready”
• Some regions allow 1-2 incomplete monitors
• Full system delete = OBD inspection failure

Diagnóstico

• DTCs indicate specific system faults
• Pending codes = intermittent issues
• Permanent codes = confirmed failures

Best Practices

• Clear codes after repairs, then drive to complete monitors
• Know your region’s readiness requirements before tuning
• Some competition vehicles are exempt from OBD requirements