[cajunfj40]

My Dad had one of the V6 TDI Touaregs. He loved it until he got a check engine light related to the AdBlue system.

TL/DR: there's a cheap heater in the tank that fails, and if it does, and the AdBlue freezes, and the engine senses "no AdBlue injected into exhaust" for long enough, it will eventually ***PROHIBIT THE VEHICLE FROM RESTARTING*** until it gets told the right things by a programmer/gets fixed/other.

It pissed him off because he lived in Alabama where it never got cold enough to worry about freezing, but when he wanted to sell the vehicle he had to get that fixed because check engine lights scare buyers.

Aside from that, he loved the economy, it drove between Alabama and Minnesota with no issues, etc.

More detail below:
(cut and pasted from a doc I put together in September of 2014, so if you already know all this, sorry, I'm not re-editing it...)

TDI Tuareg 3.0L V6 AdBlue issues:

Okay, so your Check Engine Light is on, and the dealer says it needs an AdBlue Heater. Ask what code it is, Code P202A is the one that suggests a bad heater.

There are 3 heaters: Tank heater, Pump heater and Line heater. If the dealer can tell you which particular heater has failed – or if it is a sensor – that will help. The Tank Heater is likely sold as part of the Delivery Module - not a cheap part. The Pump Heater is part of the Pump - also an expensive part. The Line Heater has two sections, one inside the Delivery Module and one along the entire line going to the injector to the exhaust - unlikely to be sold separate from those parts, depending on which part is bad. It’s just nichrome wire wound around the lines, though, so a very simple part and unlikely to fail. Same tech as a toaster.

The heaters are only to keep the AdBlue from freezing in cold weather. If the weather never gets below +12F, the AdBlue won’t freeze, and the system should work normally – but the check engine light will stay on until the heater is fixed. If the AdBlue freezes, and you have no heater, the AdBlue won't be able to be pumped - the pressure won't build up (pump or tank heater or both). If it is the line heater, the line will freeze while driving in cold weather, blocking it. (The pump and a valve drain the line after you shut the engine off, so it doesn’t stay full and freeze in the line.) Either condition means the AdBlue won't be injected into the exhaust. If that happens, your NOx reduction catalyst will perform below specification - and the NOx sensor will let the computer know something is wrong. At this point (not sure if after 3 starts or right away), the AdBlue warning light comes on with the 600 miles until No Start countdown. If a code is checked, it may be Code P20E8 or Code P204F depending on whether it senses no pressure buildup or bad NOx performance first. Unfortunately, the AdBlue warning it displays looks just like the "low AdBlue level, fill it up now!" warning, so it can be hard to tell what is actually wrong.

<SAFETY WARNING>
In any case, if that warning comes on, watch the mileage countdown. You want to be heading to a VW dealer with a nearby hotel, or home, and be able to get there within the mileage countdown shown. If the countdown gets to 0, it will warn "NO RESTART", and it *means* it. IF IT GETS TO 0 MILES, DO NOT TURN OFF THE ENGINE UNLESS YOU ARE SOMEWHERE YOU CAN SLEEP SAFELY AND GET IT TOWED - IT WILL NOT START AGAIN. Yes, that means leaving the engine running while refueling, while going in to eat, while staying in a hotel overnight someplace you don’t want to tow it from, whatever. If you turn it off after the 0 mile warning shows up, the car is stuck at wherever it got turned off until it is towed to a VW dealer (or independent shop with the correct computers to work on the VW TDI system) for repair.
</SAFETY WARNING>

There was a *HUGE* rash of TDI VW issues in the northern/Polar Vortex areas this past winter - to the point that VW basically *grounded* all TDI's using AdBlue and gave every owner that had an issue a free rental for a few weeks while they got parts on order from Europe, etc. Apparently there is an updated heater available meant for, say, Northern Canada, and/or updated code available for the emissions control computer that makes it better able to deal with colder climates. You might have a warm-weather spec Touareg TDI, and your warm-weather heater failed.

You can run without the heater so long as it stays over +15F where the car is (AdBlue freezes at +12F, the heaters come on at +23F for pump and line, and +19F for tank heater). If you plan to drive up here this winter, fix it to avoid getting stranded if it freezes up on you and locks you out. If it is the line heater that has failed, freezing solid could bust the line, making for an even more $$ repair than currently. If it is a pump heater that has failed, freezing solid may have no effect, or may burn out the pump ($$). If the tank heater has failed, freezing solid should have no further damage effect on the system – the tank is designed to accommodate freezing. It just won’t thaw out, so no AdBlue injected, so it will eventually throw the AdBlue warning at you and potentially leave you stranded when it refuses to restart after the miles counts down to 0.

Additional AdBlue note: AdBlue is VW/Audi branded Diesel Exhaust Fluid (DEF). You can buy DEF in gallon+ containers much cheaper at truck stops, WalMart, etc. and it all meets the ISO22241 standard. Some truck stops even have DEF pumps right by the diesel pumps! It will all work just the same. Do buy one of the small bottles of AdBlue from VW that has the "no spill" valve in the cap, use the bottle per the directions (IE, screw the top of the bottle to the DEF/AdBlue filler cap, press down, let bottle empty into tank, stop pressing, unscrew from tank) and then either remove the top from the bottle to refill it or cut the bottom out to use it as a big funnel to make using the gallon+ jugs easier.

Unrelated issue: Biodiesel. VW states that you can use up to 5% Biodiesel and not have an issue while keeping the 10,000 mile oil change interval. (always use "VW 507.00" approved/tested oil to avoid extremely expensive engine damage and voided engine warranty). Here in MN, we have B10 at the pump, which would potentially need 5,000 mile oil-change intervals. Check the pumps where you fill up. This is due to VW’s style of emissions control – they inject extra diesel with the main injectors so that this “wasted” fuel is shot down the exhaust to “run” the catalytic converters. This method causes fuel to build up in the engine oil, diluting it. Biodiesel does not evaporate as fast as regular diesel, so it builds up in the oil faster. B5 (5% Biodiesel) was tested by VW to show 45% oil dilution at 10,000 miles – the recommended oil change interval. Higher percentages of Biodiesel will dilute the oil faster. I can look up more on this if the pumps in your area use more than 5% Biodiesel.


Other codes/notes:

Relevant TSB 26 12 01: Check Engine Light on with code P202A, P20E8, P20B1
Code P202A: Reductant Tank Heater Control Unit Open Pending (a heater is bad)
Code P20E8: Reductant Pressure Too Low (can't build pressure, either low AdBlue, clogged line, bad pump, bad/stuck reverser valve, frozen AdBlue)
Code P20B1: ??
Code P204F: Reductant system performance (could be NOx sensor figuring out catalyst not working well)