I have a 2008 Jeep Compass. The engine light has been on for awhile. The code says it's a bad rear O2 sensor. I had the sensor replaced, but the engine light is still on. The mechanic now thinks it's the engine computer, but there are no other indications of a bad computer. I don't want to spend $800 on a new computer when the Jeep is 12yo. Why is the O2 sensor read bad, when it's brand new. Any way to get the engine light to stay off? A YouTube video says I can put a spacer between the sensor and the exhaust should turn the light off? Thanks for any help.
When you say rear O2 sensor, do you mean the down stream O2 sensor after the catalyst? If that's the case, then it could be an inefficient catalyst. A fault code for an O2 sensor doesn't necessarily mean the O2 sensor or computer is bad, you need to actually check the emissions equipment as well as the air/fuel ratios. Putting an O2 sensor spacer on a faulty O2 sensor will not turn off the check engine light if you're suggesting the computer or sensor is bad. First check the voltages the O2 sensor is reporting. The downstream O2 sensor should be at a steady 0.45 volts.
Lately I've been noticing that people want to replace sensors first when they get a fault code. A fault code doesn't necessarily mean that the sensor is bad. You ALWAYS want to look at the sensor data first and log data while driving before jumping to conclusions for any fault code. The purpose of fault codes is to let you "check" the engine...it's a "check engine light" for a reason.
@razmigb Thank you for the quick response. Yes, it's the downstream O2. I can check the O2 sensor from under the hood, without crawling underneath the vehicle and I'll check for a .45 volt meter reading. Thanks again Mr. Bartassian.
No problem! If you have a decent scantool, you can check the voltages through the OBDII. It's better to check from the OBDII because that's the voltage that the computer is reading. But you do want to make sure the voltage you check physically is the same as the voltage read by the computer.
Thanks @razmigb I have a decent OBDII scanner. The downstream O2 sensor is reading a high voltage. I'm not sure why. The car runs great and I just put new plugs in. I'm not sure what else to do get this engine light off. I checked all the fuses and relays. One relay under behind the front tire has some green corrosion on the copper stem. If you have any advice how to get the engine light to go off, reading high voltage on the downstream sensor, on a 2008 Jeep Compass, please pass it on. Thank you for your time.