Check engine lights

[Gatorstan]

While coming home from a trip both of my check engine lights came on but no loss of power checked all fluids and all was fine no over heating and good oil pressure looking for any help

 

[Rich W.]

What are you driving?

 

[Gatorstan]

2014 Discovery Cummins 380

 

[Rich W.]

On a Freightliner chassis? Any codes?

 

[Gatorstan]

SPN 4364 Fpm 18

 

[Rich W.]

That's a somewhat obscure code for SCR insufficiency, I dont think its used anymore, but it means that for whatever reason, and there are many, your SRC is not doing its job well enough. Too much difference befween the before and after NOX sensors. So its probably DEF related, unless it's a bad sensor, but DEF related could be bad fluid itself, or a bad pump, or doser (injector), or even just a plugged up DEF filter. Have you ever had emissions problems with the coach before?

There are usually several codes when a problem like this occurs, helping to narrow it down. Do you have a good code reader or are you just using the dash display?

 

[Rich W.]

Also I dont recognize FPM. Could that be FMI 18?

 

[Rich W.]

I did a little quick research and it most likely is FMI 18. Anyway, this is fairly common, and its important to do the simple and cheap things first. Change the DEF, change the DEF filter if its been a while or if it has been sitting for months without being driven. Those are cheap, its an easy job, and its normal maintenance anyway.

Your book may show a 200-300k mile interval on it, but sometimes the coach don’t read the book. Actually that interval may work for trucks that drive every day, but the way we use our coaches is different and it should be changed annually.

So those are two quick easy things you can do before spending money and starting parts swapping. Then give it five or six ingition cycles to see if it clears. It wont clear right away without code re-set equipment.

Also don’t get roped into the forced regen theory. Regens happen in the DPF which is after the SCR so it can’t have any impact on NOX sensing upstream. Its important to keep up on the DPF and do your regens, but it wont slove this problem.

If you do nothing, you will eventually experience derating and it will probably be in a couple hundred miles or less. So its improtant to get on this and see what’s going on. FMI 18 means low severity, but that’s for now. It can, and probably will change, and not for the better. You might already be at 25% derate and just not notice it. You wouldn’t unless you were towing heavy and/or climbing long steep grades.

So thats it for now. More codes would be helpful and you may need a good code reader for that. Also the ability to re-set emissions codes is nice. I use OTR Diagnostics for that but there are other non-subscription options available.

 

[Gatorstan]

Thanks for the help and taking it to a friend who has a better code reader but I think that I will drain the def tank and other than trying siphonthe tank is there a drain plug and also where is the filter and is it hard to find and get to

 

[Rich W.]

Ive read that some Spartan chassis DEF tanks have a drain, but mine doesn’t and I think that most dont. I just siphoned mine out and the waste DEF is basically liquid fertilizer so you can dispose of it accordingly. Also change the filter. Its about $120 from Cummins, but the exact same filter in a Bosch box is less than $50.

 

[Gatorstan]

I bought a filter today but I haven’t found out where’s it’s located on my 14 Discovery

 

[Rich W.]

usually the rear, bottom, center of the tank as part of the pump assembly. Check back in a few for pics.

 

[Rich W.]

This is a typical DEF pump assembly on a Freightliner chassis:

Top view

view from back of unit

The filter is behind the round cap. The pump should put out somewhere between 110 and 150 psi. My 2015 DEF went bad in 2020 and was putting out about 1 psi. So if your efforts so far don’t correct the situation, the next thing to check is pump pressure. Unfortunately there is no code to read for a bad pump; just a code for “Low DEF” of something similar, such as your SPN 4364 - insufficient NOX conversion. So it‘s the next logical thing to check and doesn't cost anything to test.

 

[Gatorstan]

Thanks Rich I’ll start looking for the pump

 

[Gatorstan]

I took my rv to a friend that has a professional laptop with a scanner and he did a regen and cleared the codes and driving back home the codes did not come back also is there a way that I could do a force regen without putting it on a scanner

 

[Rich W.]

There probably is - try looking for the “shorting plug“ described in this method:

https://www.ourmotorhome.net/2017/docs/DPF_Regen_instructions.pdf

However its important to understand that regens happen in the DPF and that piece of equipment is mounted after the SCR where your SPN code was generated. Forced regens are important, but most likely will not solve your problem. I would expect your MIL to re-activate after some driving and/or ignition cycles.

 

[Gatorstan]

I haven’t changed my def filter in my pump but am going to today is it easy to do in screw the cap and pull out the old one

 

[Gatorstan]

I. Changed my filter today and before I drove it I cleared the codes and drove it about 25 miles and no lights came back on and Rich I appreciate all the information and have you ever did force regen by using the shorter plug and is it fairly simple also the def filter was really dirty and when I first Ed cranked it back up the def tank and pump was making a noise that I’ve never heard but after couple of minutes it stopped before I drove it

 

[Rich W.]

Thats good so far and the dirty filter may have been the culprit (would like to see a pic) since it can certainly restrict flow to the doser reducing the effectiveness of the SCR, but you should probably put in a couple hundred miles of local driving to make sure the problem is resolved before setting out on a long trip. I hope thats all it was. The different sound from the DEF pump was likely the pump running dry while the system primed itself.

And no Ive never done a forced regen with the shorting plug because I can do it from my ipad with OTR, but I located the shorting plug under my dash and printed the instructions from that link in case I ever need to do it. With OTR diagnostics, I dont have to wait until the HEST lamp illuminates, so I can do forced (parked) regens whenever I want as a preventative measure as long as I have an internet connection.

Pic of my shorting plug, left side under dash next to the OBD port complete with “regen” label to avoid confusion:

 

[Gatorstan]