helimech

2001 A4 1.8t. Getting a code PO171 (lean bank 1). Scanner freeze frame shows short term fuel trim 1 as + 7.0. Long term fuel trim as + 22.6. Below that it shows short term fuel trim 3 at - 100.6 and long term fuel trim 3 at - 100.6 This is at 2400 rpm and 24.7 percent load. My question is " what is the difference of fuel trim (1) vs fuel trim (3)?" The first fuel trim readings (1) are positive numbers adding fuel. The second fuel trim readings (3) are very high negative numbers and removing fuel. Does anyone know what fuel trim (1) is vs fuel trim (3)?