jpawela Posted December 16, 2008 Share Posted December 16, 2008 Okay so here goes. I was traveling to my favorite mountain village and while going there my check engine light came on. I was climbing a steep hill against some head winds and the elevation was about 7000+ft. The first time I noticed it, I pulled over to do a visual inspection of the engine bay. Everything seemed fine and the engine idled/ran fine. The light vanished once I restarted the engine but reappeared when I continued toward my destination. When I started to go home, where all I did was coast down hills and travel on a flat freeway, there was no light and all was well. My guess is the O2 sensor is taking a dump and trips the ECU especially when the engine is strained? BTW, my rig is a 95 SE with 106K with new timing belt and tune-up Any other ideas? Link to comment Share on other sites More sharing options...
adamzan Posted December 16, 2008 Share Posted December 16, 2008 Check the ecu for codes, it will have stored one, there is a thread in the garage to show you how. Good luck Link to comment Share on other sites More sharing options...
edicer2 Posted December 16, 2008 Share Posted December 16, 2008 I agree with you its the O2 sensor my parents landcruiser would have the same problem climing hills and we got the check engine light code checked and it was the o2 sensor. It also did it on our old toyota camray when cruising down the highway or climbing a hill. I think its a safe bet to replace it and it is 13 years old so it has over a decage of gunk build up on it. Probably a good idea to change it anyways i did on my 92 and i noticed a power gain because it must not of been running right. Link to comment Share on other sites More sharing options...
Precise1 Posted December 16, 2008 Share Posted December 16, 2008 Yep, check the ECU codes first. O2 sensor doesn't always trip a code though, buy since the CEL light came on, there must be something there. Also, O2 sensors can be checked via resistance and can be 'cleaned' by removing them and burning any crap off with a torch... B Link to comment Share on other sites More sharing options...
Simon Posted December 16, 2008 Share Posted December 16, 2008 There was something about this posted years ago....I believe it was a TSB noting that the WD21's performed poorly in high altitudes. I can't remember what the fix was..... Link to comment Share on other sites More sharing options...
94extreme Posted December 16, 2008 Share Posted December 16, 2008 if it was o2, it'd run like crap. i don't think that is what your prob is. Link to comment Share on other sites More sharing options...
edicer2 Posted December 16, 2008 Share Posted December 16, 2008 if it was o2, it'd run like crap. i don't think that is what your prob is. the 02 sensor can start to get cloged and not work properly when under a full load. our old camery did that when climbing hills or passing ppl on the high way. once it was changed it worked great. same with our landcruiser. My guess is its the same with a pathfinder. My old z had the 02 go bad and it did run a little poorly but not to bad you can definalt ytell after you get them changed though. If i was you i would check your ecu and if nothing pops up go buy a new o2 sensor they are cheap so i wouldnt bother reusing a old one Link to comment Share on other sites More sharing options...
88pathoffroad Posted December 17, 2008 Share Posted December 17, 2008 Personally, I think it has more to do with the altitude than with the O2 sensor. The O2 could read wrong due to the thin air, triggering the CEL...could be that the sensor is fine but the thin air was too much for the ECU to calculate values for. Mine always did run poorly in the mountains and at high elevations. As far as I know there's nothing on the engine or in the ECU that compensates for elevation, only the feedback from the MAF, O2 and TPS. A turbo or supercharger would fix that problem. Link to comment Share on other sites More sharing options...
adamzan Posted December 17, 2008 Share Posted December 17, 2008 (edited) There was something about this posted years ago....I believe it was a TSB noting that the WD21's performed poorly in high altitudes. I can't remember what the fix was..... I didn't check but maybe it is in one of these? http://www.nissanforum.com/recalls-and-tsb...ar_1995/TSB.htm Oh here you go: 1995 Nissan Pathfinder Bulletin #: NTB95069 Sequence #: 45007 Date: 07/01/1995 Component Name: 061000 engine and engine cooling:engine Make: Nissan Model: Pathfinder Year: 1995 Summary: Hard/no start at high elevation and low temperature. *tw Edited December 17, 2008 by redfinder Link to comment Share on other sites More sharing options...
Simon Posted December 17, 2008 Share Posted December 17, 2008 There is one about a hard/no start condition at high altitude.....not sure if it's related or not. Link to comment Share on other sites More sharing options...
jpawela Posted December 19, 2008 Author Share Posted December 19, 2008 Well, the weather was nice enough today to check to codes. If I did it right, it came back as #14 vehicle speed sensor. (red light blinks once and the green blinked four times) What's that? Is it important? Link to comment Share on other sites More sharing options...
Precise1 Posted December 24, 2008 Share Posted December 24, 2008 Apparently your Pathy thinks so... "Vehicle Speed Sensor (VSS): The vehicle speed sensor provides a vehicle speed signal to the ECM. The speed sensor consists of a reed switch, which is installed in the speedometer unit and transforms vehicle speed into a pulse signal." You may have to replace the speedo unit. Try removing the gauge cluster assembly and checking the connections and tightening the small screws in the rear (ground) first. B Link to comment Share on other sites More sharing options...
jpawela Posted December 24, 2008 Author Share Posted December 24, 2008 ^thanks, I'll take a peek back there to see what's up (if anything) Link to comment Share on other sites More sharing options...
here4now Posted December 24, 2008 Share Posted December 24, 2008 Apparently your Pathy thinks so... "Vehicle Speed Sensor (VSS): The vehicle speed sensor provides a vehicle speed signal to the ECM. The speed sensor consists of a reed switch, which is installed in the speedometer unit and transforms vehicle speed into a pulse signal." You may have to replace the speedo unit. Try removing the gauge cluster assembly and checking the connections and tightening the small screws in the rear (ground) first. B WHAT? the VSS sends the signal to the ECU as well as the dash, if it's setting a code then it needs to be checked and if necessary replaced. Didn't notice if you had an A/T or M/T, I know on the A/T there are 2 different ones depending on tire size (31s or other). Link to comment Share on other sites More sharing options...
jpawela Posted December 25, 2008 Author Share Posted December 25, 2008 ^ it's an auto...that's interesting. Now that I think about it, it started doing this after I upgraded to 31's. Link to comment Share on other sites More sharing options...
Precise1 Posted December 25, 2008 Share Posted December 25, 2008 WHAT?the VSS sends the signal to the ECU as well as the dash, if it's setting a code then it needs to be checked and if necessary replaced. Just quoting the FSM... I've never heard of people changing them when changing wheel size. B Link to comment Share on other sites More sharing options...
here4now Posted December 25, 2008 Share Posted December 25, 2008 Just quoting the FSM... I've never heard of people changing them when changing wheel size. B people don't do lots of things they should do. Link to comment Share on other sites More sharing options...
here4now Posted December 25, 2008 Share Posted December 25, 2008 ^ it's an auto...that's interesting. Now that I think about it, it started doing this after I upgraded to 31's. as long as all 4 tires match in physical size, it should not have affected it other than the speedometer/odometer reading in accurately. the only reason I know about the VSS being different for the 2 tire sizes is because I was considering going down from 31s to 235s when I replaced my tires 2 weeks ago. anyone near chicago want to trade their like new 235s and VSS for my like new 31s and VSS? Link to comment Share on other sites More sharing options...
adamzan Posted December 26, 2008 Share Posted December 26, 2008 as long as all 4 tires match in physical size, it should not have affected it other than the speedometer/odometer reading in accurately. the only reason I know about the VSS being different for the 2 tire sizes is because I was considering going down from 31s to 235s when I replaced my tires 2 weeks ago. anyone near chicago want to trade their like new 235s and VSS for my like new 31s and VSS? Why would you want to go smaller? I got better gas mileage with my 31's even. Link to comment Share on other sites More sharing options...
88pathoffroad Posted December 26, 2008 Share Posted December 26, 2008 I went from 31's to 33's and never had any VSS problems aside from the speedo being off. Link to comment Share on other sites More sharing options...
here4now Posted December 28, 2008 Share Posted December 28, 2008 Why would you want to go smaller? I got better gas mileage with my 31's even. 235 is narrower, which will net better traction in the snow. 235 will also allow better throttle response because of better torque multiplication and lighter rotating mass. Link to comment Share on other sites More sharing options...
jpawela Posted December 28, 2008 Author Share Posted December 28, 2008 (edited) 235 is narrower, which will net better traction in the snow.235 will also allow better throttle response because of better torque multiplication and lighter rotating mass. ^that's true. I noticed a significant difference in performance when I upgraded to 31's. I think it robbed some of my torque and made my ride a little more jolty. I'm not going back, though. Also, thanks everyone for the replys. I haven't done anything about this possible problem yet as I haven't noticed any CEL or abnormal behavior of any sorts since I created this thread (knock, knock on wood please!). I've driven this thing nearly 1,000 miles since. I'm just going to ride it out and see what happens before I spend any $$$. I really want to change out my cat and exhaust soon. Edited December 28, 2008 by jpawela Link to comment Share on other sites More sharing options...
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