My afr sensor guage stopped showing any activity the other day, there was no check engine light lit up like there should have been. I connected the test connector and it indicated no failure. I proceeded to check all wires again and everything was ok. Last resort was to reset the ecu by connecting the connectors, which eventually found the fault and gave the flashing code to indicate the lamba 02 sensor had failed. Disconnected the connectors and then connected just the test connector and it would not give the flash code, the check engine light continued to just flash. I have now fitted a new sensor, reset the ecu and everything is ok now.