Can I get 2 L9637 iso9141 single-wire transceivers talking to each other with an ESP32?

Question

Eventually, I want to tap into the K-line of my Kawasaki Ninja with an (ISO 9141) OBD reader, using an ESP32 WROVER and a L9637 single-wire transceiver. To get there, I'm at the stage of confirming my L9637 chip is wired properly to my ESP32.
Here's where I am:

HardwareSerial Sender(1);   //  Serial port1 is the 'Sender'
HardwareSerial Receiver(2); //  Serial port2 is the 'Receiver'

/*
 * LilyGo TTGO T7 v1.5 pins
 *               ___________
 *    GND  RST  |           |  TXD  GND
 *    N-C   VP  |   ESP32   |  RXD   27
 *     VN   26  |  WROVER   |   22   25  (22 <- SEND-Rx)
 *     35   18  |   TTGO    |   21   32  (21 -> RCVR-Tx)
 *     33   19  |    T7     |   27  TDI  (27 -> SEND-Tx)
 *     34   23  |   v1.5    |   25    4  (25 <- RCVR-Rx)
 *    TMS    5  |           |  GND    0
 *    N-C  3v3  | WiFi+BLE  |   5v    2
 *    SD2  TCK  |           |  TDO  SD1
 *    CMD  SD3  |______usb__|  SD0  CLK
 *         (back) (+) (-) LiPo Batt Conn
 * 
 *                 ____________
 *  22 <- RX   1  |   SENDER   |  8  LI
 *        LO   2  |   L9637    |  7  Vs(12v)
 *    (5v)Vcc  3  | tranceiver |  6  K   ->-> K on #2
 *  27 -> TX   4  |_____#1_____|  5  Gnd      |
 *                                            |
 *                 ____________               V
 *  25 <- RX   1  |  RECEIVER  |  8  LI       |
 *        LO   2  |   L9637    |  7  Vs(12v)  |
 *    (5v)Vcc  3  | tranceiver |  6  K   <-<- K on #1
 *  21 -> TX   4  |_____#2_____|  5  Gnd
 *
 *    (need a 510ohm between K and Vs, and a cap to Gnd on each V)
*/

//  define Rx and TX on the 2 L9637 chips with K's connected:
//  TX is Input for K as output. RX is Output for K as input.
#define Sender_Txd_pin   27    //  to Tx on Sender
#define Sender_Rxd_pin   22    //  from Rx on Sender L9637
#define Receiver_Txd_pin 21    //  to Tx on Receiver L9637
#define Receiver_Rxd_pin 25    //  from Rx on Receiver

void setup() {
  Serial.begin(115200);

  //  init both L9637 RX's with a short HIGH-LOW
  Serial.println( "init both with Rx HIGH" );
  pinMode( Sender_Rxd_pin, OUTPUT );
  pinMode( Receiver_Rxd_pin, OUTPUT );
  digitalWrite( Sender_Rxd_pin, HIGH );
  digitalWrite( Receiver_Rxd_pin, HIGH );
  delay(300);
  Serial.println( "sending both Rx LOW" );
  digitalWrite( Sender_Rxd_pin, LOW );
  digitalWrite( Receiver_Rxd_pin, LOW );
  delay(25);

  Sender.begin(10400, SERIAL_8N1, Sender_Txd_pin, Sender_Rxd_pin);  // iso9141 baud rate
  Receiver.begin(10400, SERIAL_8N1, Receiver_Txd_pin, Receiver_Rxd_pin);
}

void loop() {
  Sender.println( 3 );    //  just an integer
  delay( 200 );
  while (Receiver.available()) {
    char RxdChar = Receiver.read();
    Serial.print(RxdChar);
  }
  delay(2000);
}

Note: I've tested the code and the ESP32 serial ports extensively. It works well. I've check the wiring on the (2) L9637 chips, properly powered, 510 ohm resistors, proper capacitors, with their K-lines connected to each other. When I Digital.Write to the Sender L9637 TX, I can see the K respond as well as the Receiver L9637 RX. But when I do the serial write, the Responder.available() never goes true. What gives?

I appreciate any assistance.