Quote from kevlo911 message"

0707
Your Maxima engine is OBD-2 compliant. All Diagnostic Trouble Codes are four digits, with the first is always 0 or 1. Therefore your "77" is actually "0707" which points to the rear Oxygen Sensor.

Your Maxima has three Oxygen Sensors. Two are front sensors, mounted in
the Y-pipe between the exhaust manifolds and the Catalytic Converter. One
is a rear sensor, mounted in the exhaust pipe downstream of the Cat.

When both front Oxygen Sensors are operating normally the rear sensor serves only to keep tabs on the Catalytic Converter. That's the reason your engine is running well. The Engine Control Module (the computer) is not using the signal from the rear sensor to control engine management functions.

End quote.

Question 1: If I read it correctly, I can simply ignore the rear o2 sensor, right? Since the Engine Control Module (ECU?) does NOT use the signal from this sensor.

Question 2: If it's not used to engine management, then why is it there?

Thanks guys,
Sam

 

He's right it is only for diagnostic purposes, The EPA or whoever governs automotive emissions requires it as part of OBDII. It monitors the Cat to be sure it's functioning correctly.

You could ignore it, but then you have to stare at that annoying CEL all the time. It's easy to replace and not terribly expensive so I would just replace it. Then if you have another more serious problem and the CEL lights up you know about it.

 

You can ignore it (and the car will run just fine), but if the CEL is on, you may not pass smog test. Also, if something is wrong with the catalytic converter, you can't tell. Like he said, this sensor is for keeping tab on the catalytic converter.

 

Thanks MAXimumHP. Do you know where I can get a not too expensive rear o2 sensor?

Sam

 

Not sure, but I should be looking too. I have the same problem at the moment. Oxygensensors.com I think is one web site. Otherwise Courtesy Nissan should have them, that's where I was thinking of going. Since you probably can't search, if I find a good lead I'll post it here.

 

i got my rear oxygen sensor at courtesy nissan for just under $80. i think it DOES affect the gas mileage. i always calculate my mileage at every tankful, and i know that over this last summer, the mileage went down to about 23 - 24 mpg (it used to be at 26 - 27mpg), and then on the first tankful after i put the o2 sensor, the mileage has come back to 26. obviously, ii will be monitoring the fuel economy to see if it stays at 26 from now on (hopefully).

a couple things i think might be helpful.. removing the oxygen sensor was a pain in the butt (it was the original factory sensor after 110000miles). the wrench size is 22mm, but a regular wrench was too big to allow movement to loosen the sensor. i had to get a 7/8" (fits 22mm almost exactly) flare nut wrench from sears. and i still had to pry on it like crazy... dont use your scissor jack to lift the car, you can reach the sensor from the driver's side, just by laying on the ground by the driver's door. instead, use the scissor jack to prop up the exhaust pipe, since you are going to be pushing it down when you apply force to loosen the sensor.

most importantly, do this when the car is HOT. the hot exhaust pipe will make it easier to loosen the sensor.

good luck,

tommy

 

I just bought both front O2 sensors from www.oxygensensor.com for 120ish bucks, the same that courtesy nissan wanted for each front one. I don't remember the prices for the rears, but they are definitely cheaper than Nissan.

 

Sorry, that's www.oxygensensors.com (notice the s at the end)