What Transfer Case Control does
Transfer Case Control is an Elite function built for the Polaris RZR's all-wheel-drive system. The driver flips a switch to ask for AWD or 2WD, but the ECU only makes the change when vehicle speed is low enough. That protects the front drive from engaging at a speed where it would shock-load the driveline, and it means a bumped switch at speed doesn't suddenly change how the car handles.
The function has two tabs in ESP: Wiring, where you assign the relay output and the switch input, and Settings, where you set the speed limits. It relies on a working vehicle speed signal, so set that up first. See vehicle speed sensors.
Wiring tab
Output: driving the control relay
Pick a free output for the transfer case control relay. That's usually a DPO (digital pulsed output), though a stepper output can also be used. The ECU switches the relay, and the relay handles the current. Don't run the transfer case actuator straight off an ECU output.
Active State sets the polarity:
- Low (default): the ECU grounds the output wire when the function wants the output on. This is what you want for a normal ground-switched relay.
- High: inverted. The wire is grounded when the output is off and released when it's on. Only use it if your relay logic calls for it.
AWD switch input
The driver's switch can go to either an SPI (synchronized pulsed input) or an AVI (analog voltage input). A tidy option is a Haltech dual switch panel, but any robust on/off switch works.
| Setting | What it does | Our advice |
|---|---|---|
| If you use an SPI | ||
| Edge Select | Which way the signal moves when the switch is turned on | Falling if the switch connects the input to ground. Rising if it feeds voltage to the input |
| Sensor Type | How the input reads the signal | Hall Effect for any switch |
| Pullup | Holds the input at a voltage when the switch is open | On for a switch that grounds the input, so "off" reads as a clear high voltage |
| If you use an AVI | ||
| Switch On Voltage | The voltage the input must cross to count as ON | Well clear of the switch's resting voltage |
| Switch Off Voltage | The voltage the input must cross back past to count as OFF | Well clear of the switch's active voltage, leaving a gap between the two |
Choosing AVI switch voltages
The two thresholds create a dead band. The input has to go all the way past the ON point to switch on, and all the way back past the OFF point to switch off. Anything in between keeps the last state. That gap is what stops electrical noise or a slightly dirty contact from flicking the function on and off.
Here's how we pick them. Measure (or look up) the voltage the input sits at with the switch off, and with it on. Then put each threshold a comfortable distance in from those levels, not right on top of them.
- Switch grounds the input when on (sits near 5V with the pull-up, drops near 0V when pressed). The ON threshold is a low voltage close to ground, and the OFF threshold is a high voltage close to 5V. ON triggers when the voltage falls below the low value, and OFF when it rises back above the high one.
- Switch feeds voltage when on (sits at a low or middle voltage when off and rises when pressed). This is the reverse. The ON threshold sits above the resting voltage, and the OFF threshold sits between the resting voltage and the ON value.
Whichever way your switch works, check the real on and off voltages in ESP's live data before you set thresholds. Don't assume them. A switch that shares a ground with other loads can sit a little higher than you expect.
Settings tab: when the change is allowed
| Setting | What it does | Our advice |
|---|---|---|
| Engagement: Max Speed | With the switch turned on, the ECU waits until vehicle speed is below this before switching from 2WD to AWD | Low. Engagement is the hard moment for the driveline |
| Dis-engagement: Max Speed | With the switch turned off, the ECU waits until speed is below this before going back to 2WD | Set it to a speed where the handling change won't surprise the driver |
The request is stored, not dropped. If you flip the switch at speed, nothing happens until you slow below the limit, and then the change goes through. Make sure whoever drives the car knows that, so they aren't surprised when AWD engages as they slow for a corner.
Troubleshooting
| Symptom | Usually |
|---|---|
| Switch does nothing | Vehicle speed is above the max speed, the input is assigned wrong, or the SPI edge is backwards |
| AWD flickers on and off | AVI thresholds are too close together, or the switch or its ground is intermittent |
| Works backwards | Active State is set wrong for the relay, or the edge or thresholds are reversed |
| Switches at the wrong time, or never | Vehicle speed reading is wrong or missing. Check the speed sensor setup and compare live data with actual speed |
Building out a RZR or another off-road machine on an Elite? Our other function guides, like boost control and the torque model, are worth a read. There's also a Nexus version of Transfer Case Control, and if you'd like help, get in touch.
