Readiness monitors (I/M readiness)
Definition
Readiness monitors are the self-tests the ECU runs on emission-related systems: continuous monitors (misfire, fuel system, comprehensive components) run all the time, while non-continuous ones (catalyst, lambda sensors and heaters, EVAP, EGR, secondary air) need specific conditions such as a cold start, steady cruise or an overnight soak. Each monitor reports complete or not complete, and an emissions test station will reject a car with too many incomplete monitors, since clearing codes or disconnecting the battery resets them all to not ready. To set them, drive the manufacturer's drive cycle; the EVAP monitor is the slowest because it needs a quarter to three-quarter tank and a cold ambient start. A monitor that never completes points to a fault the ECU has not yet confirmed, an enabling condition that is never met (e.g. thermostat stuck open blocking the catalyst monitor), or a pending code blocking dependent monitors. Related codes: P1000 (Ford, monitors incomplete), P0128 (prevents readiness), any pending code in the affected system.