Here is some background - my '08 RX400h was in a fender bender and the shop replaced both transmission oil cooler and trans. oil cooler pump (part 35300-48011). When I was replacing transmission oil, I noticed that the oil pump, as well as the trans cooler, were absolutely cold, whereas the transmission itself was warm/pretty hot to touch. It made me think something might have been wrong with the oil cooler pump, as you'd think it should be on at all times circulating oil from the tranny through the cooler and back to the tranny, thus making trans oil cooler at least a little warm Am I wrong? Perhaps there is some sensor in the tranny that controls when the pump is on? The car is driving fine, I don't notice any abnormalities. I'd appreciate any feedback as I can't seem to find any information on this.

 

This must be a tough question. Does anyone have a link to the electrical diagram that shows trans oil cooler pump connections? It should show whether there are any sensors in the picture with this pump. I'm planning to take 2000+ miles trip in the next month and really don't want to get stranded anywhere. Thanks for your help.

 

You could pay for techstream for a day and get access to the factory service manual. There just is not a lot of info available for these systems. Not much goes wrong. If it were mine, I would check for voltage and or sound with a mechanics stethoscope. An IR thermometer might also help. Until I saw your post I never realized there was a pump for the tx fluid but I just noticed it on the other side of the frame rail. Keep in mind, not all 400s even have that cooler. Only ones with the tow prep package. It may only cut on during extreme situations. The transmission is also cooled by the hybrid cooling system.