Rear Differential and Your Transmission Swap
This post talks about the rear differential (rear diff) temperature sensor. We explain what it does and how it can effect a transmission swap or aftermarket DCCD controller install as well as differentiate between the two types for those who just need a replacement on a STi.
What is the Rear Differential?
There are three differentials in any AWD Subaru: front, center, and rear. The front diff transfers power to the front two wheels. The center diff controls the transfer between front to back. The rear transfers power to the rear two wheels.
The ratios of the rear and front diff have to match. Generally people will refer to this as the final drive ratio. Common final drive ratios are 4.44, 4.11, and 3.90. So when installing a new transmission with a different final drive make sure the rear differential is swapped to match.
How does the Rear Diff Temp Sensor Effect my DCCD Controller Install?
In a factory STi, the rear diff temperature sensor is tied into the DCCD. If the rear diff temp sensor gets too hot, the light on the gauge cluster will turn on and the DCCD will automatically open the center diff. It's basically just an on/off switch based on temperature. We believe Subaru installed this as a safety measure.
When running an aftermarket DCCD controller install like a DCCDPro, this feature is not utilized. If desired,the rear diff temp sensor can be wired up to make the light on the gauge cluster work but it isn't necessary.
If I want to get the Rear Diff Temp Light to work on my Cluster, What Do I Do?
To get the light to work, all that is needed is to wire up the sensor to the cluster and ground it. Use the connectors below based on the year of the temp sensor and connect them to the sensor on the back of the rear diff. Then run the signal wire up to the correct gauge cluster location. The wiring to the cluster changes year to year so look at the wiring diagram when installing. The final step is to ground the sensor. On the older model temp sensors (2001-2014), a separate connector is used for the ground. On the 2015+ temp sensor the signal and ground are combined into a single connector with signal wire to the cluster and a ground wire to the sub frame.
(diagram above is for 2001-2014 Rear Diff)
(diagram above is for 2015+ Rear Diff)