# 328d Regen Concern



## NJDieselNut (Dec 15, 2016)

I got my CPO 2014 328dx sedan December 31st, 2016 with 43,500 miles on it. I'm now at nearly 70,000 miles and I have to say I've never really noticed a regen cycle. My Previous Passat TDI would regen and it was noticeable. The engine fan would come on and idle speed would be slightly higher.

During the week I do a lot of highway driving to work and back, round trip is about 100 miles. I'm wondering if the car regens primarily when I'm on the highway or driving around. My Passat would always do it when I neared home or work, and I'd notice it when I parked because of the fan and higher idle.

I've read about bad thermostats being a possible issue with regens not occurring. It doesn't seem to have an unreasonably long warm up, and there aren't any other issues or check engine lights. 

Is this normal not to really recognize a regen in the N47 engine? Do they primarily happen during longer drives? I'm just wondering if I should get the thermostat checked out. I don't have icarly or any other ECU reading device installed.

Thanks for any suggestions.


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## n1das (Jul 22, 2013)

I have never been able to notice regens in either of my diesel BMWs. The whole process is amazingly transparent....like it's supposed to be.

14 535d: At 96k miles and climbing.
12 X5 35d: At only 171k miles and climbing.

I'm the only driver of my cars (wife doesn't drive) and I split the miles up between my cars.

Make sure the engine temperature is around 88C like it should be and regens should be happening. A regen should occur around every 500 miles of driving. Long hard runs on the highway are best for it. "Drive it like you stole it" applies. :thumbup:

Good luck.


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## NJDieselNut (Dec 15, 2016)

Thanks David. I do drive it like you do yours


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## Michael47 (May 9, 2014)

There is nothing at all noticeable about a regeneration on my 2012 X5 35D. I can tell when one occurs only if I have the Blue Driver dongle inserted and am monitoring the exhaust gas temperature, which will go from the vicinity of 300°C to around 500°C. But there are no other clues as far as I can tell, and I've put about 50,000 miles on this car since we bought it at 32,000 miles.


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## drsamdds (Oct 19, 2010)

Could someone please explain to me what a regen is ? 
I have x5d '15 I'm at 17k mi and have never heard of this before 


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## glangford (Dec 11, 2013)

I've never noticed it on my 328d. One question, relative to possible thermostat issues. Does the BMW not throw a code for a stuck open thermostat. I got a check engine light one time in our Honda accord. Took it in and it was a code for open thermostat. Apparently if it takes more than a specified amount of time for the coolant to get to temperature, a code is thrown. Does BMW not do this?


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## Doug Huffman (Apr 25, 2015)

drsamdds said:


> Could someone please explain to me what a regen is ?
> I have x5d '15 I'm at 17k mi and have never heard of this before


Called to breakfast place holder.

Your diesel has a Diesel Particulate Filter that collects soot chunks and burns them to ash when conditions are right. Conditions may be right passively while at speed with an appropriately hot engine/coolant/exhaust system. The ECU may periodically command a regeneration burn. An external computer may command the ECU to perform a regeneration burn.


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## mattebury (Feb 2, 2014)

drsamdds said:


> Could someone please explain to me what a regen is ?


A simpler explanation is that a diesel engine produces soot (carbon), you see that black cloud coming out of older big rigs when they accelerate from a standstill. The diesel particulate filter traps that soot instead of dumping it into the air. When the filter becomes clogged with soot, the engine computer will initiate an active regeneration cycle. An active regen cycle causes the exhaust gas temperature to increase sufficiently (roughly 1,000 degrees F) to burn the trapped carbon and "unclog" the filter. To do that, and this depends on the manufacturer, unburned diesel is introduced into the exhaust stream where it ignites and increases the temperature of the exhaust gases sufficiently to burn off the carbon trapped in the particulate filter. The other way for this to happen is the passive method Doug mentions. When the engine is operating at freeway speeds or climbing a long grade, there can be sufficient heat produced naturally by the engine to burn off the trapped carbon without the need for an active regen cycle.


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## floydarogers (Oct 11, 2010)

glangford said:


> I've never noticed it on my 328d. One question, relative to possible thermostat issues. Does the BMW not throw a code for a stuck open thermostat. I got a check engine light one time in our Honda accord. Took it in and it was a code for open thermostat. Apparently if it takes more than a specified amount of time for the coolant to get to temperature, a code is thrown. Does BMW not do this?


BMW does. However, our diesels warm up very slowly, especially under light loads (freeway driving is light load). A few people have provided direct evidence that (especially during winter), they never warm up at all. We'd be getting all sorts of false errors if the algorithm was too rigid.


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## FastDEW (Aug 26, 2017)

Been driving my X3 for the passed 3 tanks, so that is about 1200 miles. I do a lot of highway. I have not noticed any regen cycle, so I assume it must be doing it on the highway drives. Seems great to me that it doesn't start it when I pull into my garage and heat everything up. I like the way BMW has it calibrated.


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## drsamdds (Oct 19, 2010)

thanks guys. Haven't hit that yet. I'm at 18k so it's prob coming soon.

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## imtjm (Oct 5, 2004)

if you hear your engine fan stay go on when you turn off your car, your car had probably been doing a regen.


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## Michael47 (May 9, 2014)

drsamdds said:


> thanks guys. Haven't hit that yet. I'm at 18k so it's prob coming soon.


I got news for you: at 18,000 miles, it's already happened several times. Most folks who monitor for it, have the gear to see it, and know what they are looking for say that it happens every 200-500 miles depending on driving conditions.


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## drsamdds (Oct 19, 2010)

Edit I only have 15k mi after all. 


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