FYI DEF issues

[Creeksidesouth]

My husband and I have a 40 ft 2011 Allegro Bus. We bought it in 2019. We have been experiencing major problems with the DEF unit and have been stranded or limped more times than I like. We have replaced 4 DEF heads, 3 DEF coolant sensors, a DEF pump, the DEF filter, one DEF tank and it has been in the shop 8 different times. We are on our Colorado trip and the DEF yellow light went on again. After a couple hours it started beeping - nothing consistent - but sometimes once every couple of minutes and other times once every 5 or 10 minutes. This is getting real annoying. Anyone have any suggestions.

 

[Rich W.]

Normally I wouldn’t reccomend parts swapping as a means of diagnosis but since it seems you’ve tried everything else, perhaps you have a doser problem. But before going down that route, do you have a code reader or a means of displaying codes (FMI, SPN) on your dash? Also what amber light (MIL) exactly is being displayed on the dash?

Malfunction Indicators:

This is an example of the doser used by Freightliner (engine specific):

OEM Cummins ISX15 DEF Doser Injector | 4309349 | Cummins ISX15 | Dale's Super Store

New OEM Cummins ISX 7th Fuel Injector 4309349 for aftertreatment system, Ready to Install. One Year Warranty

dalessuperstore.com

 

[Rich W.]

I just realized you are most likely on a Powerglide chassis in which case you have a different DEF system. Can you verify that? Either way, codes are where we start. Here’s a brief primer on code reading: What are SA SPN FMI - Beginners guide to fault codes

Aslo since you said “yellow light” and “beeping” are you sure its the same MIL as previous DEF warning lamps, or could it be a DPF warning this time? This is an important distinction and if thats the case (never heard of beeping associated with a DEF lamp) there are things you can do now to solve the problem. DPF warnings include an audible warning - a dinging on my FL chassis coach. Also is there a check engine lamp (CEL) associated with all this?

You may already have this but if not Chapter 4 covers the basics on your emissions system: https://tiffinmotorhomes.com/uploads/owner-manual/Allegro-Bus-Manual/Allegro-Bus-Chassis-Manual.pdf

 

[Creeksidesouth]

I just realized you are most likely on a Powerglide chassis in which case you have a different DEF system. Can you verify that? Either way, codes are where we start. Here’s a brief primer on code reading: What are SA SPN FMI - Beginners guide to fault codes

Aslo since you said “yellow light” and “beeping” are you sure its the same MIL as previous DEF warning lamps, or could it be a DPF warning this time? This is an important distinction and if thats the case (never heard of beeping associated with a DEF lamp) there are things you can do now to solve the problem. DPF warnings include an audible warning - a dinging on my FL chassis coach. Also is there a check engine lamp (CEL) associated with all this?

You may already have this but if not Chapter 4 covers the basics on your emissions system: https://tiffinmotorhomes.com/uploads/owner-manual/Allegro-Bus-Manual/Allegro-Bus-Chassis-Manual.pdf

Thank you again. Yes, we have a Powerglide chassis.

 

[Creeksidesouth]

Finally able to get a mobile repairman to diagnose the problem and reset the codes. The code was 1713 which indicates a problem with the heater control valve for the DEF unit. We replaced ours in June 2023.

 

[Bigblockyeti]

DEF delete sounds like the best option right before the very first problem arises. You must have the patience of Job if it took that number of failures to the point it was getting real annoying, I would have been supremely furious the very first time.

 

[Joe Hogan]

Here is an interesting diagnostic procedure for a heater valve issue

 

[Joe Hogan]

If you never travel In freezing temps, how important is this heater loop? I understand it manages temp of DEF fluid, but what temp range?
that said, there is always the chance of freezing temps on your traveling around the country in shoulder seasons Or mountains.

 

[Rich W.]

Finally able to get a mobile repairman to diagnose the problem and reset the codes. The code was 1713 which indicates a problem with the heater control valve for the DEF unit. We replaced ours in June 2023.

Unfortunately DEF tank heater control valve failures are fairly common and when they fail they fail open, cooking the DEF and rendering it ineffective and causing all kinds of emissions system havoc. For those scratching their heads on the code 1713 in this case, the SPN is 3363.

The cure for this is to install a manual valve in the inlet side of the engine coolant loop (which provides the heat for the tank) or simply by-pass it all together. As Joe pointed out, unless you travel in sub-freezing temps the heater is not even needed. DEF starts to turn to slush at 12°F. The DEF tank heater is really a feature needed for truckers and has no place on an RV but its part of the emissions system.

So best to by-pass it or install a manual valve on the inlet side (and leaving it off) if you think you’ll ever drive in those temps. A cheap easy fix. Deleting the DEF system, while and attractive concept in some ways is very expensive and can limit maintenance and repair options to non-factory shops since legit shops are technically not allowed to works on rigs with the emissions system removed. A valve or even bypassing the tank heater loop will not raise any red flags.

If one were to go down the delete road, this can be accomplished with software (shops in Canada provide this service under the general heading of ECM tuning) leaving the system intact but eliminating the possibility of derate, although again, this would most likely be immediately detected with diagnostics by any shop, so it still may cause issues getting other service and/or repairs. But believe me BBY, I get it!

 

[Rich W.]

To make matters worse, many units were delivered with the two heater lines (supply and return) reversed from the factory causing DEF system failures and prompting this NHTSA publication - a good read whether you plan to by-pass your tank heater, install a manual valve, or just for general knowledge should you have this issue.

https://static.nhtsa.gov/odi/tsbs/2017/MC-10130820-9999.pdf