Originally Posted by 2LT
thomasd923's public profile states his rig is a 2011 Thor Four Winds Siesta - so it is probably on a 2010 MB Sprinter chassis.
Well armed with that info the engine is most likely a CD16 version equipped with ADBlue system which of course has DEF fluid injection into the exhaust system.
The reasons for the light to come on and even warn of a 'shut down no start' condition are possible when the system goes south".
Obviously without a scan report its hard to state what might be the problem(s) but suffice to state the whole exhaust system is riddled with sensory parts to contain soot & NOx production and control it.
Ostensibly the "milestone" in corrective repairs recently was to re-program the delivery of DEF fluid into the SCR refractory unit, since condensation was found to be cracking the ceramic structure of the sensors. There are two of them! They are about $500 each!
The controlling of the system is at heart three thermo couples found in the system. There is in fact four, but forget the first one by the EGR valve for this discsussion. Each one is reporting on thermal conditions within the system.
To my knowledge these have been changed three times so part number updates are important.
The big frustration for many including the dealers is that you need about 200 mile plus of road testing to see if the whole system is functional and doesn't throw codes. Frankly who has time to drive a customer's Sprinter 200 miles plus in the drive cycles to see if the blessed lights will come on or not !
I have known several which have needed in excess of 500 miles to throw lights!
These are emissions related problems and should be covered by mandated warranty coverage to emissions control equipment.
Always be on the 'strong side' if you are asked to pay for the repair costs.
Some dealers have been charging the customer for this work which adds up to a wallet flush if you are not careful. The thermo couples alone are $200 each. It is easy to rack up a $3000 bill to fix some of this stuff.
All the best