Farthest distance before derate

[Butte64]

A friend has an apparent DEF sensor failure. He does not have a simulator but has read a procedure which he believes will take him all the way home without derate. I think he is taking a huge risk. I have seen several stories about the distance traveled before derate but never anything that is a first person experience of the longest distance traveled before derate. Anyone have that information?

[777 Driver]

When the failures were running rampant, Pat Bauer posted this:


"How to Survive a DEF Sensor Fault"

So you get a dreaded Diesel Exhaust Fluid (DEF) Fault Code? What are you going to do? Having just completed a big rally, this was perhaps the most asked question. There are lots of rumors floating around out there that need to be debunked, but I’m not going to do that. Instead, let me pass on the FACTS that I’ve learned.

Shaw is in their 7th generation of DEF sensors, and so far, they seem to be working, but Gen 4, 5, & 6, not so much. The sensors are federally mandated, and our engines will de-rate down to “limp mode” of 5 mph when they fail. The only work-around is replacement of the DEF Head Sensor. The sensor is built into the unit, but the sensor itself can be replaced…and not have to do the whole thing. DEF is a pretty stable substance until it exceeds 125°F, whereupon it begins to release ammonia, an extremely corrosive substance. Unfortunately, that can severely decrease the service life of the sensor. That single sensor monitor’s three different values and can generate three different fault codes:

SPN#3364 – FMI9 DEF QUALITY
SPN#3031 – FMI9 DEF TEMPERATURE
SPN#1761 – FMI9 DEF TANK VOLUME

So when the DEF light turns on indicating a problem, NOTHING happens for the first hour…you just have a warning…but know the clock is ticking. After the first hour, the engine de-rates by 25% for the next two hours. You probably won’t even notice a decrease in performance at 25%. At the fourth hour, however, the Engine Control Module (ECM) will de-rate the engine by 40%, and again, you probably won’t notice that unless you’re traveling in some pretty hefty hills. After the 40% de-rate, the ECM goes into the 5 mph “LIMP MODE.” Now in a 40% de-rate, you can run INDEFINITELY, unless one of these 3 things occur:

1. You idle for more than one hour;
2. You turn off the engine;
3. You fill your diesel WITHOUT also filling your DEF fluid. The ECM Looks for that!

If any of those three conditions occur, your engine will de-rate to the 5mph LIMP MODE. Of course, if you get the SPN#1761 – FMI9 DEF TANK VOLUME, you cannot recover from that and it goes into LIMP MODE. So to continue traveling under these conditions, DON’T LET ONE OF THOSE 3 CONDITIONS OCCUR! Keep going! If you need to fill up, LEAVE THE ENGINE RUNNING….AND…fill your DEF TANK too. Keep driving until you land somewhere safe where you can have the problem addressed safely.

Pat Bauer
 

[Butte64]

Thanks Stu, that is what my friend and I have been reading. But it is not clear how long that procedure will work and I have read so many times of those who were derated and shutdown I think it must not be without a limit.

[777 Driver]

Jerry, it looks to me that it's more time and condition related than distance. HOWEVER, one of the triggers is fueling WITHOUT topping off the DEF. IF you fuel WITHOUT topping off the DEF, you'll derate to 5MPH/1,000RPM.

There's a Catch-22, though. IF the failure of the DEF header prevents the DEF header from reporting DEF quantity to the ECM, when you fuel, the ECM will NOT see that the DEF was topped off and you'll derate.

At least, that's how I read it.

I have no personal experience to confirm that.

Good luck.

Take care,
Stu

P.S. Will we cross paths in MT? I'll arrive there in late June and be there until early August. We were soooo close last summer!

[Archer2]

If I recall correctly what Stu posted is right except for the part about avoiding the derate by filling the DEF tank when you fill the Diesel tank. That’s not correct. If the ECM detects that you have increase the diesel fuel tank level by more than (I think) 5% it will still go into full derate. The DEF sensor that reports the DEF level is dead and so it cannot tell the ECM whether or not you added DEF anyway.
—-EDIT—-
I just saw that Stu posted some additional info while I was typing. The bottom line is that once the sensor fails there is no practical way to avoid the ECM derating the engine performance other than:
1. Replace the Sensor
2. Have Cummins install the temporary ECM software calibration that was approved by the EPA as a stopgap if your vehicle qualifies
3. Build or obtained a DEF Sensor Simulator to avoid the derate until you can have the sensor replaced.

[brobox]

It is a total crap shoot the mileage that can be obtained. I've have seen posted as little as 200, as much as 800. Archer2 did mention the Cummins can put and emergency code in, but the could be a double sided sword. They could force the repair at a Cummins facility by ordering the part to be shipped there before applying the code. But it is doable to be able to drive home comfortably.

After two DEF head failures, I carry a full insurance policy, the simulator.

[RVFunlovers]

If your friend already has a full tank of fuel and is in range of home without turning the coach off maybe it is possible.

That worked for me. Stressful long drive but never dreamed.

But I had two simulators with me that I had made but not tested.

I put them on one at a time in my driveway and they worked.

I then got my DEF head replaced at Spartan. My DEF heater valve had stuck open which caused the head failure.

Chuck nailed it. Carry a simulator.

[MS60ocb]

Originally Posted by 777 Driver

Now in a 40% de-rate, you can run INDEFINITELY, unless one of these 3 things occur:

1. You idle for more than one hour;
2. You turn off the engine;
3. You fill your diesel WITHOUT also filling your DEF fluid. The ECM Looks for that!

Is the idle time, accumulating or reset each time you up to speed.
A person may have to watch the number of potty stops.


On my previously owned FL with the 8.9 350 HP, the Catalyst failed at about 400 engine hours. In 2017 it took about aweek to get the replacement. The problem then was Diamer-Benz had purchased some bad catalyst. The Dodge pickups were amoung the earlier failures. Any idea what this round of failure is caused by?

[Ambetter]

When I had the Gen 6 fail it was early Sunday morning, imagine that, and I continued driving for 150 miles to an RV park we found. I couldn’t tell for sure, but engine didn’t seem to have full torque. It still ran at highway speed, but didn’t seem to have as much pickup.