You have DB9 female connector at the end of the cable which is attached with Pioneer. If it would be my malfunctioning project, I would exercise the following steps very carefully to isolate the fault:
1. Disconnect the cable from the PuTTY terminal. Short the pins as indicated in the following diagram (Fig-1).
Figure-1: Signal signatures of DB9 connector for UART Port
2. Place a MAX232 chip on the breadboard and complete the following circuit. I would remain very careful about the polarities of the 1uF filter capacitors.
Figure-2: RS232 < ------> Converter
3. Make a connection between UNO and Fig-2 as per following diagram (Fig-3).
Figure-3: Connection between UNO and RS232 Coverter
4. Use DVM and measure DC voltage at Pin-2 and Pin-6 of RS232 chip. the voltages should be around (+6V to +10V) and (-6V to -10V) respectively.
5. make the following connection between Fig-1 and Fig-3.
Figure-4: Connection among UNO, RS232, and DB9-Female
6. Apply power (should be separate AC/DC connection) to the Pioneer and reset it.
7. Convert the following sketches into meaningful/rational sketch and upload into the UNO.
(a) Intialize the software UART and UART ports at Bd 9600.
(b) If no data (XON/XOFF) has arrived from pioneer, send "44VL" to pioneer.
(c) If XON (0x11) has come from Pioneer, send "44VL" to Pioneer.
(d) If XOFF (0x13) has come from pioneer, wait until XON (0x11) comes from Pioneer and then send "44VL" to Pioneer.
7. Reset bothe UNO and Pioneer.
8. Bring in Serial Monitor of UNO to view XON/XOFF/nothing
9. Send the string 44VL to pioneer from the OutBox of the Serial Monitor. The sketch of Step-7 must accommodate this option.
And Good luck for myself!