HitMan Posted October 1, 2012 Share Posted October 1, 2012 Would running rich cause the O2 sensors to trip? I think I might be having that problem. Another idea would be I think the thermostat might be going bad causing the vehicle to not get to operating temp causing the sensor to trip? Either way is a thermostat hard to change out and is there an easy check for running rich? Let me know what you think. Link to comment Share on other sites More sharing options...
Slartibartfast Posted October 1, 2012 Share Posted October 1, 2012 The thermostat is a ways in... it's something usually done with a timing belt change, and you'd be wasting your time not to do the belt etc while you were in there. If the engine isn't getting to temp, it could stay in open loop and run rich... but it's supposed to do that, and it shouldn't throw a code. Watch your temp gauge and see if it's acting funny. More likely is that the sensor is buggered, or the wiring is loose/corroded. A bad O2 or buggered wiring could make it run rich. Link to comment Share on other sites More sharing options...
Towncivilian Posted October 1, 2012 Share Posted October 1, 2012 (edited) Is your service engine soon light illuminated? The thermostat is not difficult to access; see steps on page LC-10 of the factory service manual. I would only use an OEM part for its replacement. Test it by boiling it in a pot of water (see inspection steps on that same page for details) before installation. Edited October 1, 2012 by Towncivilian Link to comment Share on other sites More sharing options...
HitMan Posted October 1, 2012 Author Share Posted October 1, 2012 I changed the sensor over a year ago, but the issue still keeps coming back. Only is an issue in the cool/winter weather. Have been running all summer with no issues or tripped light. Now getting to the fall weather and cooler temps the CEL sets off again saying its the O2 sensor again. Always codes Bank1 Sensor 2, which is the one I replaced. The temp gauge stays below the midpoint in the cool weather, but in the summer it stays perfect in the middle. Everytime the temp gauge stays below the midpoint the CEL comes on again. Getting tired of clearing the code, so was thinking the thermostat was going bad according to the temp read out. Link to comment Share on other sites More sharing options...
Towncivilian Posted October 1, 2012 Share Posted October 1, 2012 (edited) Sensor 2 is the rear oxygen sensor. What is the specific code? It might just be the sensor's heater element being faulty, it might not necessarily be an issue with your emissions system or engine operation. The upstream oxygen sensor would detect any engine issues. Edited October 1, 2012 by Towncivilian Link to comment Share on other sites More sharing options...
pathfounder Posted October 1, 2012 Share Posted October 1, 2012 Would running rich cause the O2 sensors to trip? I think I might be having that problem. Another idea would be I think the thermostat might be going bad causing the vehicle to not get to operating temp causing the sensor to trip? Either way is a thermostat hard to change out and is there an easy check for running rich? Let me know what you think. Is there something specific that makes you think the engine is running rich? Does it drink fuel or have black and/or smelly exhaust? Lean misfires can create the illusion of running rich, so there's that. The way to tell rich/lean is with an oxygen sensor, really. You can change the thermostat, a $10 part, but there is stuff in the way. Follow the upper rad hose to the engine, it's in the metal spherical part. If you can get to the bolts that hold it in, you can replace it. Just beware that you need to drain the block or it will leak coolant everywhere... Link to comment Share on other sites More sharing options...
Alkorahil Posted October 1, 2012 Share Posted October 1, 2012 The outside temperatures seeming to be a factor make me think thermostat or engine temp sensor. (or both) Link to comment Share on other sites More sharing options...
HitMan Posted October 4, 2012 Author Share Posted October 4, 2012 It is a P0136 O2 Sensor Circuit Malfunction (Bank 1 Sensor 2). Yes it drinks fuel as it is a pathfinder haha, but not more than normal. The outside temp change and the engine not getting up to normal temp during normal operation is the big concern. makes me think the thermostat because in the summer this problem never happens, but in the winter it does. Weird right? I got this idea from: Normally the rear oxygen sensor's voltage changes slightly when the fully warmed-up engine is accelerated (rich mixture) or decelerated (lean mixture). If the voltage from the rear O2 sensor doesn't change as expected for a certain period of time, the code P0136 is set. This could be caused by a faulty oxygen sensor itself, corrosion in the sensor connector, problem with the sensor wiring, exhaust leak or a number of other causes. Sometimes a too lean or too rich condition can trigger the code P0136. Checked the wiring and everything when I replaced the new sensor, which I did in the winter and the code still tripped again a few days after the replaced sensor. I don't think the cat is going bad because during the summer I don't have a problem. So I think it might be running rich causing the trip because the engine temp is running slightly below normal. I'm gonna attempt the thermostat and see if that takes care of the temp problem. Where is the engine temp sensor located? Should I try that as well? Link to comment Share on other sites More sharing options...
Towncivilian Posted October 4, 2012 Share Posted October 4, 2012 Loosen and retighten engine ground screws: I found no TSBs relating to this issue. The FSM lists these possible causes: Harness or connectors Rear heated oxygen sensor Fuel pressure Injectors Intake air leaks So, check for intake air leaks and run a 20oz bottle of Chevron Techron in the gas. You can check the resistance of the ECTS; reference values are on EC-103 and the harness location is a few pages down. Link to comment Share on other sites More sharing options...
HitMan Posted October 5, 2012 Author Share Posted October 5, 2012 Awesome I'll take a look and see what I can find. Could very well be a cracked intake line somewhere. Thanks for the help! Link to comment Share on other sites More sharing options...
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