Check Engine Light - DTC 0156 O2 Sensor

21tgs · Oct 10th, 2002, 07:43 AM

1996 Pathfinder, 103,500 miles

This past weekend I drove roughly 900 miles to and from North Carolina. I’ve made this trip many times over the years, but this time on my return trip the check engine light came on and has been on since Sunday. I own an OBD-II scanner. When I check the DTCs I can see that I have only one code, the code is 0156. Code 0156 is a malfunctioning O2 (oxygen) sensor, specifically sensor 2 in bank 2. Bank 2 is the driver’s side of the engine. Sensor 2 is the non-heated sensor behind the catalytic converter.

Knowing this I turned to my service manual. Specifically the G-codes with tests section. I performed all of the tests and found no fault, broken or shorted wire pertaining to this O2 sensor. I thought may be it was a fluke so I erased the codes. During the next drive cycle the check engine light came on again. Once again I used my scanner to check the codes and again I have a code 0156. I looked through the manual again to see if there is a test for the O2 sensor itself. The only O2 sensor tests in the book are for the HO2 sensors (heated oxygen sensors). Thinking that I might have a bad sensor I went to the dealer and I bought a new sensor, installed it and erased the codes from the computer. Once again, during the next drive cycle the check engine light came on.

Has anyone else had this problem? How were you able to fix the problem?

It is my understanding that the O2 sensors behind the catalytic converter check the O2 content of the exhaust to ensure that the catalytic converters are working and this might be a sign that my converter is degrading. Posts from a search with www.dejanews.com have yielded a bad tank of gas, a faulty fuel injector or a loose gas cap may trip the sensor. My guess is that I have nothing to loose by checking the spark plugs and while I have them out I’ll run a compression check. The spark plug wires, ditributor cap and rotor have less than 5,000 miles on them. I’ll be checking the resistance in the wires just to be sure that they’re fine. I change my spark plugs on a regular basis and I always use the OEM recommended NGK plugs.

I am open to any suggestions than you may have.

Jason

Oct 10th, 2002, 11:33 AM

....did you mean you reseted the computer? If not the you may need to unhook the negative terminal on your battery for up to 24 hrs for it to reset. I've seen this happen on other cars when the O2 sensors were changed but the CPU was not allowed to reset. Hope that helps! Good luck.

BORNGEARHEAD · Oct 10th, 2002, 09:47 PM

I would bet that if you replace your o2 sensor and clear the code you will be fine. If your catalytic converter is going bad you should get a code for"catalyst...". If your plugs are bad or misfiring or incorrectly gapped you would get a misfire code for that specific cylinder. If you don't tighten your gas cap enough you will get a code for "evap small leak". Your o2 sensor can have a number of things happen that will give you this code. Sticking open, sticking closed.... If you have a scanner, why don't you monitor the o2 sensors and see how they are operating?

21tgs · Oct 15th, 2002, 11:54 AM

An update regarding the O2 sensor and the check engine light (MIL).

What I found while searching www.dejanews.com is that the Canadian government has performed tests on various fuels to find that Exxon fuel has a relatively high sulfur (S) content. I couldn’t believe that Exxon fuel was my problem, but at the same time I don’t buy Exxon in my home town, I buy Sunoco. While on the trip that caused the MIL to illuminate I bought fuel from 3 different Exxon stations.

I am now running a fresh tank of Sunoco fuel. I used my OBD-II scanner to erase the code from the computer and the MIL has remained off for nearly 100 miles and several drive cycles. I guess that may be it was the Exxon fuel.

PatScottAKA99XE · Oct 18th, 2002, 07:13 PM

Quote:

Originally posted by 21tgs
An update regarding the O2 sensor and the check engine light (MIL).

What I found while searching www.dejanews.com is that the Canadian government has performed tests on various fuels to find that Exxon fuel has a relatively high sulfur (S) content. I couldn’t believe that Exxon fuel was my problem, but at the same time I don’t buy Exxon in my home town, I buy Sunoco. While on the trip that caused the MIL to illuminate I bought fuel from 3 different Exxon stations.

I am now running a fresh tank of Sunoco fuel. I used my OBD-II scanner to erase the code from the computer and the MIL has remained off for nearly 100 miles and several drive cycles. I guess that may be it was the Exxon fuel.

Wow, that is very interesting. Im gonna have to look into this. I am a automotive tech and have never heard of this. Hmm.
There are ways to test non-heated O2 sensors. One is with a real good DVOM(Digital Volt Ohm Meter) and with a data display capible scan tool. I prefer the DVOM method. I have found that unless you have a mfg. specific scan tool(Consult for Nissans) the refresh rate tends to be too slow to accuratly "watch" O2 sensors. For instance, I work at a GMC dealer so we have the GM Tech II, for all the other stuff that comes in we have a Snap-On Mt2500(?). I find the refresh rate of the Tech II pretty damn good, the MT on the other hand is horrible. This is why for non-GM stuff I preffer to use my Fluke 88 DVOM(god, I love that thing).
If your problem comes back drop me a line and Ill try to help you diag that thing. If it doesnt, thats great!