I have some codes on my 2019 Nissan Altima indicating a problem with the forward sensor. I was told it was fixed but the codes are still there. How can I tell if this problem existed before I bought the car?
If the check engine indicator wasn't covered or someone removed the lamp or led, any error would turn on the indicator. If a repair was made, addressing the error code(s), some error codes may require up to three engine run cycles (cold engine startup, drive, hot engine shutdown - three times) before the CEL/MIL turns off. Readers may or may not display 'PENDING', indicating several drive cycles needed to turn off the CEL and erase the code(s). Regular errors should turn off the CEL and erase the code(s)reset from memory. Another issue may be if a reader or battery disconnect was performed; this erases emissions parameters learned during everyday driving with the CEL off. The vehicle emissions systems is reset back to factory parameters and the vehicle must be driven in city and highway modes as well as local traffic for as much as 50 miles for the emissions system to relearn all new parameters. This might be displayed on readers as 'READY' or 'NOT READY' status. Some emissions monitors learned while driving; engine coolant temperatures, O2, map, throttle position. If all parameters are within range of programmed values, a 'READY' status is displayed - the vehicle will pass state and federal emissions.