The Nissan Path

I have a 2006 Pathfinder SE 4x4; it shifts normally when the O/D is off, but when I turn it on it will shift up to 4th normally, but when it tries to go into O/D around 50mph it downshifts to 3rd. If I let off the gas to allow it to shift, nothing happens...it stays in 3rd until I turn the O/D off, then it will shift to 4th.

I checked the tranny, fluid looks good; not burnt and not frothy. I checked the coolant also to be sure it isn't mixing with ATF, and it too looks good. ATF level is good.

I can hear a hissing sound near the back of the intake near the firewall...it appears to be a leaking vacuum line that heads toward the tranny. Would a vacuum leak cause it to do this? I thought it's all electronic and based on the TPS.

Thanks for your help!

I don't think so. The transmission is electronically controlled. But I could be wrong.

Hopefully I'll have time to fix the leak tomorrow and test it out. I'll update the post then. Thanks!

I fixed the vacuum leak, but this did not solve the OD issue. I'm thinking it's the TPS. I just bought this, and the previous owner said he disconnected the battery to clean the terminals...I'm thinking he did it to clear the CEL. Anyway, I'm going to try and reset the TPS this afternoon...hopefully that does the trick!

The battery was unhooked for more than 24 hours. No codes but it still won't shift into 5th gear. I've read in the AT manual that it might be the revolution sensor in the transmission. Has anyone else had this problem?