Also do this:
- disconnect the NGK from your FlashScan;
- connect the AD1+ pin to the AD1- pin and see what the pid EXT.AD1 says (in volts);
- connect a 1.5V AA battery to the AD1+/- and see what EXT.AD1 says, and at the same time measure the voltage using a DMM;
- tape two 1.5 AA batteries together, and repeat;

post the results here (what EXT.AD1 says and what the DMM says) for those three cases:
- AD1+/- shorted:
- 1.5V AA battery:
- 3.0V AA battery: