Oxygen Sensor and gas mileage
is it for emmisions
it is to see how much oxygen is in the exhaust. to much 02 (lean, not enough gas) so the car will send more gas to make the mixture right.
to little 02 (rich, to much gas) means there is smog (unburned gas) which is bad for the environment, so it reduces amount of gas.
if one is bad then you could be running rich which will give bad gas mileage. but if one is bad you would get a SES light.
it is to see how much oxygen is in the exhaust. to much 02 (lean, not enough gas) so the car will send more gas to make the mixture right.
to little 02 (rich, to much gas) means there is smog (unburned gas) which is bad for the environment, so it reduces amount of gas.
if one is bad then you could be running rich which will give bad gas mileage. but if one is bad you would get a SES light.
The reason I'm asking is because my gas mileage has been going down. I got an SES light for a bad o2 sensor. They reset the light and since then it hasn't gone back on. But the gas mileage continues to be crappy. I'm trying to figure out if I replace the o2 sensor which may or may not be bad, if that will help with my mileage.
Originally Posted by steelymatt
The reason I'm asking is because my gas mileage has been going down. I got an SES light for a bad o2 sensor. They reset the light and since then it hasn't gone back on. But the gas mileage continues to be crappy. I'm trying to figure out if I replace the o2 sensor which may or may not be bad, if that will help with my mileage.
and the code for that is still stored even if the light is off. so the light wont come back on because it already told you there was a problem.
replace the sensor right away, its bad!! if it wasnt, the light would never have come on.
You can have a poor-performing O2 sensor without the SES light coming on, so long as the O2 sensor is still working within the ECU's acceptable parameters. If the O2 sensor is not working as well as before, your fuel economy may drop. If the SES light HAS come on recently with the O2 sensor code, then it's conclusive that an O2 sensor could indeed be going bad.
So you're saying that if I had the SES reset and the sensor is bad, it won't trigger the SES light again? I wanted to be absolutely sure the o2 sensor was bad before I had it replaced and I'm still waiting for the light to come back on. It's been about 3 weeks.
Originally Posted by steelymatt
So you're saying that if I had the SES reset and the sensor is bad, it won't trigger the SES light again? I wanted to be absolutely sure the o2 sensor was bad before I had it replaced and I'm still waiting for the light to come back on. It's been about 3 weeks.
you will wait forever, it wont come back on
if the light came on with a 02 code then yes, it is bad. replace it
Senior Member
Joined: Jan 2004
Posts: 419
Originally Posted by soonerfan
no it wont trigger the light again, it already did. it does it once, if you reset it the light goes off but the code is stored for you.
you will wait forever, it wont come back on
if the light came on with a 02 code then yes, it is bad. replace it
you will wait forever, it wont come back on
if the light came on with a 02 code then yes, it is bad. replace it
Soonerfan, thanks for your replies but I think you're wrong. The SES can come back after it is cleared if the sensor is still bad. Look at this post I found:
http://forums.maxima.org/showthread....&highlight=ses
http://forums.maxima.org/showthread....&highlight=ses
Originally Posted by soonerfan
no it wont trigger the light again, it already did. it does it once, if you reset it the light goes off but the code is stored for you.
you will wait forever, it wont come back on
if the light came on with a 02 code then yes, it is bad. replace it
you will wait forever, it wont come back on
if the light came on with a 02 code then yes, it is bad. replace it
I believe the procedure goes roughly like this (may be a little different as far as exact numbers, but here's the general idea)
If a problem occurs during one run of the vehicle (ignition start to ignition stop), a "ghost" code is stored. You can view this via an OBD-II scantool. SES light does not come on.
If the problem continues during a second run of the vehicle, the SES light comes on and the code is now an active code, not a "ghost" code.
If the problem condition ceases for 2 or 3 consecutive runs of the vehicle, the SES light will disappear and I believe the code will clear. However, if the condition happens again for 2 consecutive runs of the car, the SES light will come back on.
------------
Here's the specifics. "Two-trip detection logic" (from AlldataDIY, which I believe is a copy of the Nissan shop manual)-
DTC and 1st Trip DTC
The 1st trip DTC (whose number is the same as the DTC number) is displayed for the latest self-diagnostic result obtained. If the ECM memory was cleared previously, and the 1st trip DTC did not reoccur, the 1st trip DTC will not be displayed.
If a malfunction is detected during the 1st trip, the 1st trip DTC is stored in the ECM memory. The MIL will not light up (two trip detection logic). If the same malfunction is not detected in the 2nd trip (meeting the required driving pattern), the 1st trip DTC is cleared from the ECM memory. If the same malfunction is detected in the 2nd trip, both the 1st trip DTC and DTC are stored in the ECM memory and the MIL lights up. In other words, the DTC is stored in the ECM memory and the MIL lights up when the same malfunction occurs in two consecutive trips. If a 1st trip DTC is stored and a non-diagnostic operation is performed between the 1st and 2nd trips, only the 1st trip DTC will continue to be stored. For malfunctions that blink or light up the MIL during the 1st trip, the DTC and 1st trip DTC are stored in the ECM memory.
Procedures for clearing the DTC and the 1st trip DTC from the ECM memory are described in "Clearing Trouble Codes".
For malfunctions in which 1st trip DTCs are displayed, see "Two Trip Detection Logic". These items are required by legal regulations to continuously monitor the system/component. In addition, the items monitored non-continuously are also displayed on CONSULT-II.
1st trip DTC is specified in Mode 7 of SAE J1979.1st trip DTC detection occurs without lighting up the MIL and therefore does not warn the driver of a problem. However, 1st trip DTC detection will not prevent the vehicle from being tested, for example during Inspection/Maintenance (I/M) tests.
When a 1st trip DTC is detected, check, print out or write down and erase (1st trip) DTC and Freeze Frame data as specified in "Work Flow" procedure Step II. Then perform "DTC Confirmation Procedure" or "Overall Function Check" to try to duplicate the problem. If the malfunction is duplicated, the item requires repair.
http://spirilis.net/gallery/2000-Max..._pattern_table
(disclaimer: Note that this image came from AlldataDIY, and they have a copyright notice on the page, so I will take this image down if I ever hear any trouble regarding it
)
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