OBD-II UART Adapter + UNO + TWI 2004 LCD

First off, nice work on everything so far (hardware and software). I've been enjoying it!

So, I seem to have come to a bump in the road concerning the use of a "non-supported" LCD.

LCD: [url=http://www.sainsmart.com/sainsmart-iic-i2c-twi-serial-2004-20x4-yellow-lcd-module-shield-for-arduino-uno-mega-r3.html]I2C/TWI LCD2004[/url]

Previously, I've been using the ZT OLED (from you) with zero problems as a boost gauge. I wanted something more visible in daylight, so I chose the 2004 with yellow backlight.

I am trying to use liquidcrystal_i2c.h as I was able to get my Nano working with the LCD using this library to verify the LCD works without OBD-II adapter. As soon as I move the LCD over to the UNO in place of the ZT OLED (and replace multiLCD library with liquidcrystal_i2c), I fail to see a display.

What I've noticed is that with the OBD-II UART adapter plugged in, I cannot even run the

I2C scanner ([url=http://playground.arduino.cc/Main/I2cScanner]http://playground.arduino.cc/Main/I2cScanner[/url]) successfully

[code]

#include <Wire.h>


void setup()
{
Wire.begin();

Serial.begin(9600);
Serial.println("\nI2C Scanner");
}


void loop()
{
byte error, address;
int nDevices;

Serial.println("Scanning...");

nDevices = 0;
for(address = 1; address < 127; address++ )
{
// The i2c_scanner uses the return value of
// the Write.endTransmisstion to see if
// a device did acknowledge to the address.
Wire.beginTransmission(address);
error = Wire.endTransmission();

if (error == 0)
{
Serial.print("I2C device found at address 0x");
if (address<16)
Serial.print("0");
Serial.print(address,HEX);
Serial.println(" !");

nDevices++;f
}
else if (error==4)
{
Serial.print("Unknow error at address 0x");
if (address<16)
Serial.print("0");
Serial.println(address,HEX);
}
}
if (nDevices == 0)
Serial.println("No I2C devices found\n");
else
Serial.println("done\n");

delay(5000); // wait 5 seconds for next scan
}
[/code]

Questions:

[list type=decimal]
[*]Should I instead be using your MultLCD library ([url=https://github.com/stanleyhuangyc/MultiLCD]https://github.com/stanleyhuangyc/MultiLCD[/url])?
[*]Can I duplicate and modify class LCD_1602 in MultiLCD to support this LCD?
[/list]

Here's where I might start(?)

[code]
#include "LCD4Bit_mod.h"
class LCD_2004 : public LCD_Common, public LCD4Bit_mod
{
public:
byte getLines() { return 4; }
byte getCols() { return 20; }
void writeDigit(byte n)
{
write(n >= 0 && n <= 9 ? '0' + n : ' ');
}
void clearLine(byte line)
{
setCursor(0, line);
for (byte i = 20; i > 0; i--) write(' ');
}
};
[/code]