Nissan Pathfinder and Xterra Transmissions have Internal Computer Control Modules
The computerized transmission controller is located inside the Nissan Pathfinder and Nissan Xterra transmission, attached to the valve body. Transmissions such as those in the Nissan Pathfinder are not the only units that house the transmission computer within it; other companies that manufacture units with this configuration include BMW and Mercedes. However, almost all other cars, trucks, and SUVs are designed with the computer located outside of the transmission, and in many cases it is integrated into the engine computer controller system.
Automatic Transmission High Current and Low Current Computer Electrical Systems
A computerized automatic transmission uses both low current and high current systems. The low current systems control the computer microprocessor itself, while the high current systems control the shift and pressure solenoids. If the computer controller is located outside of the automatic transmission, only high current electronics are located within the transmission. If the controller is located on the inside, then low current electronics are located on the inside as well.
Radiator Leak Causes Transmission Problems on Nissan Pathfinder, Xterra, and Armada
These categorical differences play a big role in the high failure rate of Nissan trucks and SUVs, specifically in the Pathfinder, Xterra and Armada with the RE5R05A unit. This is because the transmission cooler heat exchanger located inside of the radiator often develops a leak. The radiator leak problem is internal and allows the engine radiator fluid, or water based coolant, to mix with the automatic transmission fluid. On most automatic transmissions, transmission fluid that is contaminated with water based radiator coolant does not affect the high current electronic solenoid systems.
Valve Body Damaged by Radiator Coolant Water Leak Must Be Replaced on Nissan Transmissions
For most trucks and SUVs, fixing the radiator problem and replacing the transmission fluid might correct this problem. However, on the Nissan Pathfinder and Xterra and other models that use the RE5R05A transmission, the engine coolant water contamination can short-circuit the low current electronic computer located on the valve body. We have found that fixing the radiator and replacing the contaminated fluid with fresh fluid does not alleviate the problem, as the transmission computer has been permanently damaged. The only way to fix a damaged transmission computer is to replace it with a new one, and they are only available from Nissan as part of a new valve body assembly. We also recommend bypassing the radiator with an external transmission cooler to prevent this from happening again as replacing the radiator issue is likely to happen again.