Have a 2001 jeep grand Cherokee check engine light was on for bad oxygen sensor replaced the oxygen sensor and have drove it probably 300 miles and scan tool says not all monitors are ready so can't pass emissions did replace battery because was at 25%life still made no difference what gives computer refuses to reset what gives please help
The engine light is not going to reset until the computer has all monitors ready, especially the one for the o2 sensor. Some emissions codes cannot be cleared manually even when you reset the computer by disconnecting the battery. The monitors may not be ready because the issue is not fixed.
@razmigb
The check engine lights is not on and has no codes just the monitors won't reset
Ok. Can you please specify which monitors are not resetting? All or just some? For some vehicles, readiness monitors require performing a "drive-cycle" where you have to drive half an hour on city streets and half an hour on the highway and at certain speeds. You can look up what the drive-cycle is for your vehicle if it has a specific one. Most of the time you just have to keep driving it, but I ask these questions to figure out whether there is an actual issue with the systems or just an improper drive-cycle performed.
@razmigb
No monitors are resetting and This : to best of my knowledge , the drive cycle(s) were done correctly . I approached my mechanic about getting a waiver , but he blew me off.
@razmigb
Edit : only monitors that are incomplete are o2 and catalyst
@ssims_92
Which o2 sensor did you replace? Pre-cat, post-cat or both? It seems like the monitors are not ready because there is an issue with either the o2 sensors or the catalyst(s). Usually those monitors are the quickest to be completed if they don't have any issues. I would first make sure that the data from the oxygen sensor is good and that it is screwed in tightly. You don't want any exhaust leaks near it. The o2 sensor should operate between 0.1 and 0.9 volts, where 0.1 is lean and 0.9 is rich. It should be fluctuating very rapidly and should not be slow. If it staying below 0.5 volts or stuck at one voltage, then the sensor should be replaced. Post-cat sensor should be a steady 0.45 volts. They should be OEM quality. Please keep me posted. Any smoke coming out of the exhaust? And how are the fuel trims?
@razmigb
Replaced both upstream sensors. ,both were oem sensors . As for voltage & fuel trim(s) , my code reader isn't set up for voltage readings. Perhaps taking it to a more competent mechanic would be able to reveal that . I'm still fuming. ,no pun intended , that the previous mechanic would just blow me off
@ssims_92
I totally understand. Some mechanics out there are scammers and are not trustworthy. This is why I learned how to do everything on my car myself. We all need to be more mechanically inclined so that mechanics cannot fool us. If your scanner has a live data menu, you should be able to see the voltage and fuel trims. If not, then I guess taking it to an honest mechanic would be best. If you're interested in doing maintenance on your car, it's beneficial to have a scantool that reads live data, especially while you drive it around. I use the OBDLink MX+ bluetooth scanner, and it's awesome! Anyway, I hope you solve your issue soon. Continue to keep us posted!