Explanation of "Engineering Test Mode" codes?

Don't have documentation, but a lot of the raw data codes (fuel, temp, etc) appear to be based upon a 0-255 scale which is common in electronics (one byte in hex / binary)
thus 0 = 0 and 255 = max. Generally you will never see the extremes, so a full fuel tank indication is 248ish on my car. I don't know if that's a mechanical limitation of the sender, or headroom intentionally built into the scale.

As for the other codes, no idea

delete the double post