I’m trying to get the REAG_LVL (DEF Fluid Level) from , and it works, but I dont understand the response…wondering if someone can break down how to read the bits/bytes for this example?

Full spec is:

A = Byte 1 of 10
A, bit 0 = Avg Reagent Consumption Supported
A, bit 1 = Avg Demanded Reagent Consumption Supported
A, bit 2 = Reagent Tank Level Supported
A, bit 3 = Minutes run by engine while NOx warning mode is activated Supported
A, bits 4-7 = Reserved – 0 default

B,C = Average Reagent Consumption
0 L/h to 327.675 L/h
0.005 L/h per bit scaling
xxx.xx L/h

D,E = Average Demanded Reagent Consumption
0 L/h to 327.675 L/h
0.005 L/h per bit scaling
xxx.xx L/h

F = Reagent Tank Level
0% to 100%
100/255 % scaling
xxx.x %

G,H,I,J = Total run time by the engine while NOx warning mode is activated
0 sec to 4,294,967,295 sec at 1 sec/bit
xxxxxxx hrs, xx min

I sent a 0185 and full response is:

7E8100C418504000000
7E82100FF00000000AA

A = 04 (bit 2 set = REAG_LVL supported)
(100/255) * F = 100%

…so I got the result I wanted which was to read REAG_LVL and its at 100%…but I don’t understand the full response.

7E8 10 0C 41 85 04 00 00 00
7E8 21 00 FF 00 00 00 00 AA

I know 7E8 means engine ECU response, and I see the 04(A) and FF(F) but I don’t understand how 04 is A…and FF is F.

What bytes correspond to the respective letter in the example above? And How does it know that?