Last year, (Sept, 2014) check engine light came on with code SPN 3556 FMI7. This week the code has appeared again. Code refers to failure to light ARD (after burner)
Last year the fix was to replace a spark plug with "moderate carbon buildup." At that time, Tech ran tests on system with no negative results. Assumption was that spark plug was the problem. Seems unusual to have the same problem again so soon.
Question: is this common or is it evidence of a larger problem (eg oil in engine,). I want to take it to dealer (10 mile drive) but concerned about possibility of engine shut down. Is this a real concern for that distance or am I overly cautious?
One further note: I did get an intermittent Water in Fuel message a few weeks ago, but been running "fresh" fuel.
Your expert thoughts, please. and thanks in advance.
Engine: Cat C 13, 35,000 miles.