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Old 12-06-2021, 12:27 PM   #1
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High exhaust temp / regen

I've never owned a diesel w/ DEF so I am not familiar with this at all. I test drove a 2011 American coach / 450 cummin ISL / spartan chassis, and a short while into the drive, the info center popped up with a "HIGH EXHAUST TEMPERATURE" message along with an icon. I did not notice any difference in performance, and the message went away about 15 minutes later.

Owner said this is normal. I did some quick google searches and found that this might be normal.

My question to the RV experts is.... 1. is this definitely normal to happen during a short 20 minute drive? 2. If this happens more often / occurs a lot... is this a sign of something soon to fail or need service? such as the DPF?

Thanks.
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Old 12-06-2021, 12:34 PM   #2
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High exhaust temp / regen

No that is normal and it just tells you that the system is working correctly because it is burning off the soot caught in the particulate filter.

I cannot comment on how often it is supposed to do that compared to how healthy the DPF is. Someone else should chime in hopefully.
I do know that the more you let it sit and idle, the more often it will have to do a regen.
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Old 12-06-2021, 12:39 PM   #3
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Thumbs up

This is a completely normal operation. My ISC will show the high exhaust temp signal on occasion and is designed to do so during an exhaust regeneration process. 15 minute timing is also about right.

Enjoy the coach.
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Old 12-06-2021, 11:35 PM   #4
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People often confuse "def" and "dpf" two different emission systems.
DPF refers to diesel particulate filter it traps soot particles, it requires heat to burn the soot particles and turn them into ash. DEF if after treatment it is done generally after the dpf and uses a fluid that is njected into a chamber to reduce nox emissions
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Old 12-10-2021, 04:17 PM   #5
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Thank you for the feedback on this. Did this change on newer coaches? A friend w/ a 2016 winnegabo w/ cummins 450 said he's never seen the message... another friend with a 2016 newmar w/ cummins 600 said he's never seen that either?

Is the message for the DPF regen specific to certain years, or chassis ??
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Old 12-10-2021, 04:52 PM   #6
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Probably just a coincidence you were in it when it went into regen.

Mine will regen about every 3500mi.
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Old 12-10-2021, 04:52 PM   #7
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Kinda interested in the responses also, but I have never seen this message with our coach in the 53K miles that we have on it. We are the original owners.

With that being said, we also do not idle for long periods of time and a majority of our driving is hiway. If we needed to idle for an extended period Iíll put the coach into high idle.
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Old 12-10-2021, 04:56 PM   #8
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Mine is a pre-DEF engine, so it may regen more frequently than a newer model.
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Old 12-10-2021, 04:57 PM   #9
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Quote:
Originally Posted by EMPIRE231 View Post
Thank you for the feedback on this. Did this change on newer coaches? A friend w/ a 2016 winnegabo w/ cummins 450 said he's never seen the message... another friend with a 2016 newmar w/ cummins 600 said he's never seen that either?

Is the message for the DPF regen specific to certain years, or chassis ??
Nothing significant changed. All DPF systems do regens, but there are three distinct types of regens that happen. They are passive, active, and forced or manual regens. Each type can happen on any diesel, depending on several variables, including amount of soot, and exhaust temps during highway driving. Passive regens usually happen with no notifications whatsoever and go unnoticed. They are the lowest level of regen and if effective, that may be the only type performed for years. Little idle time and lots of smooth highway speeds encourages passive regens.

Active regens are what you experienced, and they too are normal. If lack of highway driving time or soot build up that isn’t cleaned by passive regens, lead to active ones with dash lights and messages. They should be allowed to complete their cycles.

Forced regens trigger a CEL and set a code. They require a tech with software or a special reader to activate. They happen when the other two do not satisfy the sensors.

Many reasons why you witnessed an active one, and it’s not necessarily that a failure is due. Perfectly normal, as are your friends who have never seen a message.
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Old 12-10-2021, 05:01 PM   #10
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If the HEST warning was on when someone before you shut the coach down, it will start again as soon as the engine is up to temperature. Once it starts a Regen, it takes about 20 minutes or so of highway speed driving for it to clear. On a lot of coaches, there will be a dash warning light but not necessarily a message. Mine goes through a regen about every 2500-3000 miles, or more often if there's a lot of slow traffic driving or heavy mountain climbing.
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Old 12-10-2021, 06:22 PM   #11
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Nothing significant changed. All DPF systems do regens, but there are three distinct types of regens that happen. They are passive, active, and forced or manual regens. Each type can happen on any diesel, depending on several variables, including amount of soot, and exhaust temps during highway driving. Passive regens usually happen with no notifications whatsoever and go unnoticed. They are the lowest level of regen and if effective, that may be the only type performed for years. Little idle time and lots of smooth highway speeds encourages passive regens.

Active regens are what you experienced, and they too are normal. If lack of highway driving time or soot build up that isnít cleaned by passive regens, lead to active ones with dash lights and messages. They should be allowed to complete their cycles.

Forced regens trigger a CEL and set a code. They require a tech with software or a special reader to activate. They happen when the other two do not satisfy the sensors.

Many reasons why you witnessed an active one, and itís not necessarily that a failure is due. Perfectly normal, as are your friends who have never seen a message.
Thanks Larry for the explanation. When we travel we tend to drive somewhat hard 70+mph or so over 250 to 300 miles at a time. So I assume that this is why I have never seen a regen over the miles we have driven on this coach.

I have friends who have commented on a visible regen, while driving, and my response is the same as above. I sure hope that this is the reason I donít want to have to have the DPF pulled and cleanedÖ.
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Old 12-10-2021, 10:19 PM   #12
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The responses to your question show the varying ways the engine manufacturers use lights to indicate engine regeneration performance. If you are looking at buying a coach with the newer emission systems, I would encourage you to cycle the key on and off to illuminate all the warning lights that are present. They vary from manufacturer to manufacturer and in some cases model your to model year. There is usually one yellow light that will say DPF, Filter or Regen. This signifies the DPF needs to regen. When the computer shows the DPF filter at a certain capacity, it will call for the regen process to start. If not at operating temperature and above 30 mph it will stay illuminated until a parked regen is complete. This usually takes 20-30 minutes. If the coach is taken up to higher road speeds, a passive regen will start and usually no filter light is illuminated. There is also a HEST light which stands for high exhaust system temperature. Some times it is a yellow light with a puff of air and a thermometer in the indicator or in other units it actually says HEST. At highway speeds during passive regen it will not illuminate, BUT if during the regen, you were to take an off-ramp for an exit, as you slow below 30 MPH, the HEST light will come on to let the driver know the system has been regenerating and is very hot. You would not want to park over dry grass at that point. If a mechanic was doing a road test, this light would let him know to be careful if he needed to get under the coach to inspect his work. When regenerating, the exhaust temperatures can go up to 1200+ degrees. When the regen is complete parked or the unit slows down in passive mode, the system will cool very quickly. In some cases the HEST light might be on for just 3-5 minutes. That is why you see some responses to having may miles on the unit, with no lights ever being illuminated. In your case the light you saw is a normal event.

All that being said, if you are considering buying an 07 or newer coach, I would recommend you have a competent shop run an emission system function test before purchasing the coach. That will give you the health of the sensors, EGR valve, DPF and DEF system if applicable, as well as any active or past fault codes. On road highway tractors, one quick check we do is compare the miles to total engine hours. If the total lifetime mph is 35-40mph or better itís a good sign. If the average is less than that, then the unit was idled heavily and might need further inspection. As mentioned in earlier posts, idling is a killer on the newer emission systems. A diesel engine is designed to operate in the 180-200 degree range. At idle, many engines will struggle to hold within 40-50 degrees of that. It will not burn efficiently at lower temperatures and the DPF catches the results. Sorry for the long reply. As you can see, it can be complicated. Good luck on your search for a new coach.
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Old 12-12-2021, 10:35 AM   #13
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Thank you for the feedback here! Definitely seems like it’s something normal. I’m picking it up next week and will have a 4 hr highway drive home, so I’ll pay attention to it and see how it does during a long haul.
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Old 12-12-2021, 01:49 PM   #14
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Thank you for the feedback here! Definitely seems like itís something normal. Iím picking it up next week and will have a 4 hr highway drive home, so Iíll pay attention to it and see how it does during a long haul.

Many drivers donít notice the high exhaust temp warning. Or it just doesnít give that warning at all. Like mentioned it depends on the manufacturer. But rest assured they all regen and get extremely hot during regen. Frequent forced parked regen is a sign that the DPF is requiring more than a passive regen and this can be a bad sign. Less idle time, and more freeway time, keeping rpms up, helps keep your DPF healthy.
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