What happens to the truck if DEF goes past expiration? I can't believe it would damage the system in any way. Does it matter if it's not as effective?
I borrowed this information from another site it is not my info, but here is what I got from the op on the other site.
Clean Diesel vehicles use closed loop control to manage the Selective Catalytic Reduction (SCR) system that is part of the after treatment system. In principle, it is like cruise control in your vehicle: With cruise control, you set the desired speed, and the vehicle does all the work to maintain it: increase throttle setting, decrease throttle setting, etc. With clean diesel SCR, the control system is set to control the amount of oxides of Nitrogen: NOx in the exhaust.
The system injects (doses) a very accurate amount of DEF into the exhaust upstream of the SCR catalyst many times per second just like a fuel injector. The urea in the DEF is converted to ammonia by heat, and the ammonia then reacts with the catalyst to convert NOx to water, nitrogen, and CO2. The system also works with the EGR system to provide the best efficiency (lean burning) conditions in the engine to improve fuel economy. There is a NOx sensor after the SCR module that measures NOx in the exhaust. If the NOx levels are too high, the pulse widths or frequency of the DEF doser are increased, adding more urea to the exhaust stream. It is important to not inject too much DEF in the exhaust, or ammonia will be present in the exhaust, not good. All these actions take place hundreds of time per minute.
So what are the implications of diluted, very old, or otherwise non-conforming DEF??
Well, in most cases you will simply use more of it, just like your cruise control applies throttle to climb a grade. The required levels of NOx in the exhaust are maintained. In cases where the SCR system cannot meet mandated levels of NOx in the exhaust, you'll get a message, and be required to fix the issue within a specified length of time, usually something around 200 miles (varies widely by OEM, but all must comply with EPA2013 protocols).
Addressing the issue means adding DEF if you ran out, or having the system repaired, perhaps by flushing the DEF system or replacing a bad sensor or plugged filter. Most problems arise from users accidentally putting diesel in the DEF tank (please don't do this) or putting water in instead of DEF to save money.
Worst case: Using badly contaminated DEF or intentionally using the wrong fluid can destroy the SCR system on your vehicle. Full replacement may be required. Price varies, but can be over $5000. Way over.
Normal case of getting bad DEF at the pump or from a bad jug: Flush DEF tank, replace filter, replace sensor: from $250 to over $1000. Less if under warranty and it was a bad part or your vehicle just needs a "reflash" of the engine control computer to implement a fix in "firmware". The EPA requires 2013 Clean Diesel engine manufacturers to provide up to 70,000 mi or more warranties on the emission control systems like SCR. They are not required to cover negligence.
