Failing an emissions test due to “not ready” OBDII codes can be frustrating. This article details the troubleshooting process used to resolve this issue on a Mazda Miata, providing valuable insights for anyone encountering similar problems with their Obdii Not Ready Codes Reader. The car failed initially because the OBD-II interface reported several systems as “not ready,” including the EGR, catalyst, and O2 sensor. This guide walks through the steps taken to diagnose and fix the problem.
Verifying Basic Functionality and Initial Diagnosis
The first step was to rule out simple causes. The car’s battery had been recently replaced, and no codes had been manually reset. Driving the car more, as suggested by the emissions technician, didn’t resolve the issue. A code reader confirmed the “not ready” status, even after additional driving. Importantly, there were no active or pending codes, and the check engine light (CEL) was not illuminated.
Idle speed was checked and adjusted to the correct level, as an incorrect idle could impact emissions readings. The EGR system, being relatively easy to diagnose, was examined next.
EGR System Inspection
Several online resources provided guidance on testing the EGR system. A vacuum test confirmed the EGR valve was functioning correctly. Although the EGR boost sensor wasn’t directly checked due to lack of specific information and tools, the connecting tube was clear, and the sensor appeared to be registering vacuum. The EGR position sensor was also tested and confirmed to be working as the CEL illuminated when its electrical connector was disconnected.
Drive Cycle and Further Diagnostics
Despite these checks, a standard OBDII drive cycle, along with extra highway driving, still resulted in a “not ready” status. Attention then turned to engine temperature sensors, as the ECU relies on these readings for proper emissions system operation. All three temperature sensors were confirmed to be functioning correctly.
The puzzle remained: why wasn’t the system throwing a code if the O2 sensor wasn’t providing data? The O2 heater being “ready” suggested the issue wasn’t electrical.
Replacing the Oxygen Sensors
Finally, after exhausting other possibilities, new Bosch 15733 oxygen sensors were installed. Wiring information for the new sensors was sourced online to ensure proper installation. The old sensors, although appearing clean, were likely the culprits.
Success! Passing Emissions
After a 40-minute drive, all OBDII monitors showed “ready,” and the car passed emissions. This experience highlights a crucial point: O2 sensors can fail in a way that doesn’t trigger a CEL or set a diagnostic trouble code, leading to “not ready” OBDII readings. Replacing the O2 sensors, even without obvious signs of failure, resolved the issue. This car had 110,000 miles on the original factory sensors.
