2008 Uplander van. When I turn right signal on, why does emergency flasher come on instead?

Instead of guessing , hooking up a professional type scan tool an checking for codes in the BCM mite short cut the diagnostic time by half .
Left Front Turn Signal Control
B3948
DTC B3948 will set when the BCM detects a short to ground or an open/high resistance in the LF turn signal control circuit.
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Right Front Turn Signal Control
B3949
DTC B3949 will set when the BCM detects a short to ground or an open/high resistance in the RF turn signal control circuit.
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Left Rear Stop/Turn Lamp Control
B3950
DTC B3950 will set when the BCM detects a short to ground or an open/high resistance in the LR turn signal control circuit.
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Right Rear Stop/Turn Lamp Control
B3951

DTC B3951 will set when the BCM detects a short to ground or an open/high resistance in the RR turn signal control circuit.

Check for a short in the rear bulbs

Either the emergency flasher has been turned on accidentally or there is a defective multifunction switch.