Originally Posted by josiahg52

I can't be sure if the Liqui-Moly additives have done anything for me but since I've been using it regularly, no more deNOx system efficiency codes. It may be masking the problem. The code seemed to come in on hotter days at 40mph or faster when decelerating with the engine. It wasn't very often but enough to get my attention.

The DEF capacities:
Passive 15.8L / 4.2 gal
Active 5.5 L / 1.5 gal

Tank #1 0 miles - Super Diesel Additive (SDA)
Tank #2 600 miles - nothing
Tank #3 1200 miles - SDA
Tank #4 1800 miles - nothing
Tank #5 2400 miles - SDA
Tank #6 3000 miles - nothing
Tank #6 3600 miles - SDA
Tank #7 4200 miles - nothing
Tank #8 4800 miles - Diesel Purge (DP)
Tank #9 5400 miles - DPF Protector (DPFP)
Tank #10 6000 miles - nothing
Tank #11 6600 miles - SDA
Tank #12 7200 miles - nothing
Tank #14 7800 miles - SDA
Tank #15 8400 miles - nothing
Tank #16 9000 miles - DP
Tank #17 9600 miles - DPFP, engine and oil filter change

I get about 600 miles per tank. I put the additive in before a fill up and amend this schedule as necessary if I'm filling up before the entire tank is used, going on a trip so I might do an oil change early, etc. I use Shell diesel, BP is my second, then Sunoco and then Chevron/Texaco. Exxon/Mobil is also acceptable.

I repeat this cycle three times and then replace the diesel fuel filter. After six cycles I replace the air filter also. I top off the DEF every oil change.