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Transmission issue


okanagan
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After a two hour rest break today the automatic transmission on our 99 Pathfinder suddenly started to act up.   We tow a small travel trailer.  Transmission temp was about 150F and engine temp was normal.  ATF and filter were changed earlier this year.  Would not shift into overdrive and the torque converter would not lock.  Revs were about 1100 higher than it should have been.  Drove for about 10km and then stopped.   The check engine light did not come on but I ran the diagnostic computer anyways.  There were a few stored codes from a couple of years ago (02 sensor, evap and knock sensor) so I cleared them.  Got back on the highway and everything was fine for the rest of the day.   Seems very odd.

 

Any idea what is going on? 

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I was just wondering since 150degF is pretty low for towing with an RE4. Getting stuck in 4th is common before a failure with these transmissions but I’m not familiar with failure to shift into 4th.

To me it sounds like a solenoid issue, however I would imagine the trans temp to be very high for a solenoid issue to raise its head. Well either really high temp or really low temp.

There are some more knowledge guys, like Slartibartfast, that could probably shine some more light on your issue.

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Sounds to me that the trans was too cold. Like the engine, the trans has a normal operating temperature and when the temps are too low, the computer will prevent the torque converter from locking up and prevent overdrive. 

My 93 does it on the highway a lot when the weather is less than summer hot because I have bypassed my radiator entirely and the trans has its own large cooler. If I drove my truck more, I would be installing a thermostat in the trans cooler circuit to prevent that problem. 

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I’ve read in the factory service manual that the transmission uses 3rd gear as limp mode. But I think there is supposed to be a light in the dash to accompany it though. I would assume towing would yield higher temps than 150f. Maybe the temp should be checked at the trans cooler line where it feeds into the radiator?

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We made it home today.  1200km round trip with no further issues.   The transmission runs fairly cool because we have auxiliary cooler installed.  Transmission temperature up a long steep hill is about 180F.

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