Frustated in Havasu

[Rich W.]

The first two refer specifically to the NOX sensor in the SCR, which is where DEF is converted to ammonia which then reacts with nitrogen oxide changing it to nitrogen and oxygen. Both codes have identical descriptions on my lists so as far as I can see they redundent. But these things happen. Commonly. There are far too many codes and some are repeats.

5746 is indicating a problem with the dosing unit or dosing unit relay. There’s a bunch of sub-codes to get specific, but essentially its saying the same thing as the first two - DEF isn't doing its job probably becuase it isn't getting to the SCR, at least in sufficient quantity.

4264 doesnt seem to exist but 4364 does. This fault code sets when the Aftertreatment Control Module (ACM) detects that the NOx conversion is lower than a calibrated threshold, which relates nicely to the first three. Could 4264 be a typo?

Anyway, my expericene, FWIW, is that this is most likely the DEF pump (or possibly just the DEF filter) and not the head. A bad pump will provide low or no DEF pressure to the doser and the emissions system, as complex as it is, sees this as LOW DEF and shows up as such on the dash. It can also stump technicians, and cause them to replace the DEF head unnecessarily, clear the codes, let you get down the road about 80 miles (in my experience) and then the codes come back and you are once again headed for derate.

Have they tried to diagnose it or are they just assuming you need a DEF head because you're getting a LOW DEF MIL with plenty of DEF in the tank?

If so they have you waiting for a DEF head you might not need and probably have the pump in stock. Can you elaborate on your experiences so far (any visits to a shop? indicators on the dash? derate status?), and also if its 4364, and not 4264?

Its possible that you need a DEF head, but you have none of the typical DEF head failure codes (level, quality, temp) and you do have codes indicating DEF isnt getting where its needed. The DEF head is primarily a monitoring device that reads conditions in the tank. It includes the supply line to the pump (and filter) but unless its plugged, its unlikely to be part of the problem.

Here’s a schematic of a typical system. In this chart, the pump is listed as “supply module” next to the DEF tank. The rest is pretty much self-explanatory.

 

[Rich W.]

So, to help firm up an opinion, please indicate the following:

1. Has it been diagnosed IN a shop?

2. Did a shop provide the codes or did you get them from your LBCU (or whatever its called on a Tiffin chassis)?

3. What other indicators do you see on the dash?

4. How far have you driven since this started?

A couple key points. Right now, according to your code list, you arent derated. To delay being derated as long as possible, do not start the rig unnecessarily, do not idle any more than necessary, and do not get fuel unless necessary and if you do try to limit to to less than 20 gallons. Once the ECM decides your emission system is malfunctioning, it counts ignition cycles, times idling, and tracks fuel usage to determine how soon you should be stranded on the side of the road to atone for your sins.

Here’s a couple charts to identify various MILs:

 

[Flashflood]

The first two refer specifically to the NOX sensor in the SCR, which is where DEF is converted to ammonia which then reacts with nitrogen oxide changing it to nitrogen and oxygen. Both codes have identical descriptions on my lists so as far as I can see they redundent. But these things happen. Commonly. There are far too many codes and some are repeats.

5746 is indicating a problem with the dosing unit or dosing unit relay. There’s a bunch of sub-codes to get specific, but essentially its saying the same thing as the first two - DEF isn't doing its job probably becuase it isn't getting to the SCR, at least in sufficient quantity.

4264 doesnt seem to exist but 4364 does. This fault code sets when the Aftertreatment Control Module (ACM) detects that the NOx conversion is lower than a calibrated threshold, which relates nicely to the first three. Could 4264 be a typo?

Anyway, my expericene, FWIW, is that this is most likely the DEF pump (or possibly just the DEF filter) and not the head. A bad pump will provide low or no DEF pressure to the doser and the emissions system, as complex as it is, sees this as LOW DEF and shows up as such on the dash. It can also stump technicians, and cause them to replace the DEF head unnecessarily, clear the codes, let you get down the road about 80 miles (in my experience) and then the codes come back and you are once again headed for derate.

Have they tried to diagnose it or are they just assuming you need a DEF head because you're getting a LOW DEF MIL with plenty of DEF in the tank?

If so they have you waiting for a DEF head you might not need and probably have the pump in stock. Can you elaborate on your experiences so far (any visits to a shop? indicators on the dash? derate status?), and also if its 4364, and not 4264?

Its possible that you need a DEF head, but you have none of the typical DEF head failure codes (level, quality, temp) and you do have codes indicating DEF isnt getting where its needed. The DEF head is primarily a monitoring device that reads conditions in the tank. It includes the supply line to the pump (and filter) but unless its plugged, its unlikely to be part of the problem.

Here’s a schematic of a typical system. In this chart, the pump is listed as “supply module” next to the DEF tank. The rest is pretty much self-explanatory.

Yes I’m sorry the code is 4364. We’re not sure we are not sure of the diagnostic they’ve done. They had an issue with their diagnostic machine diagnosing the codes I ended up giving them the codes from the dashboard and I’m assuming they use those codes to diagnose the problem.

 

[Rich W.]

Is Tiffin paying for this?

If not, since your emissions warranty is expired, get an agreement in writing that if their diagnosis is wrong and/or their work doesn't solve the problem, you dont pay. Its bad enough if you have to pay to fix a known problem on a faulty system, but to pay for mistakes made by the shop is even worse, and unfortunately this is fairly common.

An “issue with their diagnostic machine” really raises red flags, especially since these codes don't indicate a DEF head issue. Seems like they are assuming or guessing since its DEF related and the head is the most common DEF system problem. Unfortunately there are other more likely possibilities.

Ive spent some more time lookimg at SPN 5746 and specifically it indicates a faulty Dosing unit heater relay, or it could even just be a fuse. I know you're probably not inclined to look at this yourself, but its worth a call to the shop. Its unfortunate the shop you went to couldn't properly diagnose before causing you this extended delay.

I have had good luck with Velocity Truck in Las Vegas and they have a shop in Kingman, and they work on “all makes”. Please keep providing updates as they happen - these things are always good learning experiences.

 

[Flashflood]

So, to help firm up an opinion, please indicate the following:

1. Has it been diagnosed IN a shop?

2. Did a shop provide the codes or did you get them from your LBCU (or whatever its called on a Tiffin chassis)?

3. What other indicators do you see on the dash?

4. How far have you driven since this started?

A couple key points. Right now, according to your code list, you arent derated. To delay being derated as long as possible, do not start the rig unnecessarily, do not idle any more than necessary, and do not get fuel unless necessary and if you do try to limit to to less than 20 gallons. Once the ECM decides your emission system is malfunctioning, it counts ignition cycles, times idling, and tracks fuel usage to determine how soon you should be stranded on the side of the road to atone for your sins.

Here’s a couple charts to identify various MILs:

1. I don’t believe it’s been diagnosed in a shop because they had a problem diagnosing it with their computer.
2. I got the codes off the dashboard.
3.Amber engine light came on pulling into town .
4. Less then 30 miles , driving back from the shop the red engine stop light came on .
Unfortunately we filled up when we got into town and the amber light was on.

 

[Rich W.]

1. I don’t believe it’s been diagnosed in a shop because they had a problem diagnosing it with their computer.
2. I got the codes off the dashboard.
3.Amber engine light came on pulling into town .
4. Less then 30 miles , driving back from the shop the red engine stop light came on .
Unfortunately we filled up when we got into town and the amber light was on.

I just edited my last post with this:

Ive spent some more time lookimg at SPN 5746 and specifically it indicates a faulty Dosing unit heater relay, or it could even just be a fuse, and according to one report, it caused a red stop engine light. I know you're probably not inclined to look at this yourself, but its worth a call to the shop. Its unfortunate the shop you went to couldn't properly diagnose before causing you this extended delay.

Here’s the post on 5746 - interesting reading. Also on a 2015. I want to learn from this one so let's keep in touch on it.

DEF Error Codes - Forest River Forums

Hope this saves someone some pain and money... Had the following error codes from my ScanGauge D... ID: 1569 - Engine Protection Torque Derate FM: 15 - Data Valid but above normal operating range (leas

www.forestriverforums.com

While 5746 indicates ”dosing unit heater relay” it appears that in a low voltage condition (Cummins sub-code 4156) it cuts power to the dosing unit and apparently that means the whole system including the pump, and not just the doesr itself. This would explain the other codes. It also still rather strongly indicates that it is not the DEF head, I’m still interested in what warning lights came on initially and what is on now, but its not worth cycling the ignition if you don't recall.

 

[Rich W.]

And here is a little more confirmation. Note that the dosing unit relay supplies power to the DEF heater (hence 5746), but it also supplies power to everything else in the system - pump and doser included, which explains 3216 and 3226. As I said before, these are all codes that I have never seen associated with a DEF header failure.

My coach has had two bad DEF heads and one bad DEF pump, and I’ve reviewed many other cases in my attempt to take control of these faulty emissions systems. So after delaying you for over a month, most likely for a part you don't need, I think a call to the shop is in order.

 

[Flashflood]

1. I don’t believe it’s been diagnosed in a shop because they had a problem diagnosing it with their computer.
2. I got the codes off the dashboard.
3.Amber engine light came on pulling into town .
4. Less then 30 miles , driving back from the shop the red engine stop light came on .
Unfortunately we filled up when we got into town and the amber light was on.

I just edited my last post with this:

Ive spent some more time lookimg at SPN 5746 and specifically it indicates a faulty Dosing unit heater relay, or it could even just be a fuse, and according to one report, it caused a red stop engine light. I know you're probably not inclined to look at this yourself, but its worth a call to the shop. Its unfortunate the shop you went to couldn't properly diagnose before causing you this extended delay.

Here’s the post on 5746 - interesting reading. Also on a 2015. I want to learn from this one so let's keep in touch on it.

DEF Error Codes - Forest River Forums

Hope this saves someone some pain and money... Had the following error codes from my ScanGauge D... ID: 1569 - Engine Protection Torque Derate FM: 15 - Data Valid but above normal operating range (leas

www.forestriverforums.com

While 5746 indicates ”dosing unit heater relay” it appears that in a low voltage condition (Cummins sub-code 4156) it cuts power to the dosing unit and apparently that means the whole system including the pump, and not just the doesr itself. This would explain the other codes. It also still rather strongly indicates that it is not the DEF head, I’m still interested in what warning lights came on initially and what is on now, but its not worth cycling the ignition if you don't recall.

Is the Dosing unit in the head? Your help is so appreciated !

 

[Flashflood]

I just edited my last post with this:

Ive spent some more time lookimg at SPN 5746 and specifically it indicates a faulty Dosing unit heater relay, or it could even just be a fuse, and according to one report, it caused a red stop engine light. I know you're probably not inclined to look at this yourself, but its worth a call to the shop. Its unfortunate the shop you went to couldn't properly diagnose before causing you this extended delay.

Here’s the post on 5746 - interesting reading. Also on a 2015. I want to learn from this one so let's keep in touch on it.

DEF Error Codes - Forest River Forums

Hope this saves someone some pain and money... Had the following error codes from my ScanGauge D... ID: 1569 - Engine Protection Torque Derate FM: 15 - Data Valid but above normal operating range (leas

www.forestriverforums.com

While 5746 indicates ”dosing unit heater relay” it appears that in a low voltage condition (Cummins sub-code 4156) it cuts power to the dosing unit and apparently that means the whole system including the pump, and not just the doesr itself. This would explain the other codes. It also still rather strongly indicates that it is not the DEF head, I’m still interested in what warning lights came on initially and what is on now, but its not worth cycling the ignition if you don't recall.

Sorry seeing the Dosing unit is not in the head

 

[Rich W.]

Sorry seeing the Dosing unit is not in the head

No but when they say dosing unit, they are including the pump which is mounted on the outside of the tank and the doser, mounted on the SCR, and apparently the tank heater which is in the head. However the heater has its own code - 5745, so the heater relay (5746) is much more likely to be the issue.

There are also two fault codes, 4155 and 4156 associated with SPN (suspect parameter number) 5746. They both lead to the same condition and repair, but they would need to actually perform the diagnostics to get those codes.

The relay that both fault codes refer to appears to provide power for all of it and of course it is external as well. It really requires proper diagnosis which I guess they plan to do (if they have diagnostic capability) after making you wait a couple months for the DEF head in case thats the problem. I imagine you wont be too thrilled if it isnt.