Scott Johnson is the proud owner of a 2009 Nissan Pathfinder. He purchased this vehicle brand new for a specific purpose – to tow his fishing boat to his lakefront property once a month. The trusty Nissan has performed this monthly towing task without a hiccup for years. This trip involves some rigorous mountain passes and a little off-road terrain to reach Scott’s favorite boat ramp.
The RE5R05A transmission has been reliable as a Swiss-made watch until one day the transmission started to act up; the vehicle lacked power and the transmission stopped shifting. Scott was uncertain of what was happening, so he stopped by a local transmission shop in the foothills of the nearest town.
Mike, a tech at the transmission shop, scanned the vehicle and a DTC U1000 was found in the TCM. According to the OE Nissan code information, this was some type of a CAN or Controller Area Network communication problem between the transmission control module and other computer systems on the truck (See figure 1).
Common causes for setting the U1000 on these vehicles are as follows:
- Poor harness ground connections;
- Controller Area Network (CAN) communication harness is open or shorted; and
- Faulty Engine Control Module (ECM).
Mike checked and tested all the grounds and connections no problems were discovered. Mike was a bit uncertain of the OE Nissan information as it referred to using the Nissan Consult Scan tool which his shop did not have. To play it safe and not to misdiagnose the truck the vehicle was brought to the local Nissan dealership for diagnosis. The recommendation was to install a new valve body and program it.
The dealership installed the valve body and programmed it, all seemed to work fine so the vehicle was returned to the owner. A month goes by and the Nissan returns to the transmission shop with the same complaint, DTC U1000. During this go around, Mike spends some serious road test time behind the wheel with his scan tool. After hours of driving the following observations are made:
1. The code will not set if driven around town or on continuous freeway driving.
Mike asked Scott to hook up his boat and return so they can duplicate the road test together on the way to the lake.
2. The truck will only set the code with the boat in tow while traversing the mountainous pass at mile marker three.
This led Mike to one conclusion, it must be getting hot. The confusing part of this is there were no over-temp codes or warning lights on the dash indicating the transmission was running hot. Mike returned to the shop to pick up the infrared temperature gun and make another pass up the mountain.
A temperature check was made at the transmission oil pan before approaching the mountain pass, the temperature was at 185 degrees F. At mile marker three, the transmission goes into failsafe mode again. Mike quickly pulls over and measures the temperature, this time it was reading 220 degrees F. He cleared the code and let the truck run in Park for 10-minutes to allow it to cool down.
The truck was turned around and Mike headed back down the pass, the transmission performed flawlessly. Once at the bottom of the pass Mike turned around and made another trip back up. Like clockwork, the truck went into failsafe mode again after reaching mile marker three. It was suggested to install a temporary air-to-oil cooler to bypass the radiator and repeat the trip up the mountain pass. With the temporary oil cooler installed, the transmission never exceeded 198 degrees F operating temperature while pulling the boat even past mile marker three. The radiator was replaced which resolved the heating problem and DTC U1000.
The perplexing part of this problem is why was the DTC U1000 being set for an overheating condition. If we look at figure 2, this is the OE Nissan code list for this truck, there are no codes listed for an overheating condition. There are two temperature sensors in the RE5R05A transmission, one is for the transmission cooling system that is mounted on the valve body and the other is internal to the TCM, which is also mounted on the valve body (See figure 3). There is a code P1710 referring to an open or short circuit, high or low voltage regarding both temperature sensors, yet the P1710 does not refer to an over-temperature condition. The generic scan tool did not have data PIDS for temperature sensors 1 or 2.