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Discussion Starter #1
2011 xterra with 140k on 'er. I noticed heating issues with the HVAC system (blowing cold when idle) and that the engine was running a warmer than usual, especially during a long drive (~4 hours each way) over the weekend. It wasn't close to overheating or anything, just a bit hotter than usual.

Coolant flush has been on my to-do list and I suspected a possible air leak, or in a worse case a thermometer or water pump issue. Then I popped a P0171 lean code this morning and I'm wondering to what extent they might be related or if it's just a coincidence.

Are these related? If so, is it more likely a warmer engine will then cause a lean condition or more likely that running lean from some other issue will make the engine run hotter? The internet seems torn on whether a lean engine runs hot... I guess worst scenario the engine ran too hot and I blew a head gasket?
 

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1) you are low on coolant. You have every sign of it.
2) lean code should not have anything to do with being low on coolant.
 

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1) you are low on coolant. You have every sign of it.
2) lean code should not have anything to do with being low on coolant.
What he said about coolant.

As for the P0171, clear it and see if it comes back - but its more than likely your MAF sensor, although could also be a vacuum leak or 02 sensor.
 

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Dug into the x this weekend and I think I figured out what happened...

Started with a coolant flush and while I was checking out the tubes, I noticed the barb/rim on the upper radiator hose connector was completely worn down on one side. Okay so time to replace radiator - might as well replace thermometer as well...
While I was taking off the air intake, I decided to clean out the manifold and throttle body. Upon inspection of the intake manifold, I noticed the gaskets looked in pretty bad shape. Replaced those - might as well replace throttle body gasket too...

Conclusion: This is what I think happened. The seal on my radiator was worn and caused a vacuum leak. This caused the engine to run hot enough to warp the rubber gaskets at the intake manifold which caused mixing between cylinders and run lean giving the code.
All in: new radiator, new thermostat, new gaskets, coolant flush and bleed (btw FSM for this process is a little vague, I ended following https://www.thenewx.org/threads/cooling-system-observations-and-comments.35683/), then cleaned the MAF just for good measure in case of any backflow from possible mixing at the intake.

Cleared the code, drove 20 miles to work today (highway and city) and it hasn't come back so fingers crossed.


TL/DR: not in this case and I'd probably say that more often the lean code will be from another issue that has developed from the engine running hot.
 

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My car (Mitsubishi Lancer) was just throwing p0171 codes constantly. Looked all over for vacuum leak, verified it wasn't MAF, etc. Couldn't figure it out, took it in. It turns out the radiator had cracked and was mostly empty. It never showed a temp problem and I never saw coolant leaking. Mechanic insisted it was likely the cause of the problem and it obviously needed to be replaced so went ahead and did it. The code stopped.


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