In very cold weather, should I idle until the RPM settles down? - Page 4 - Chevy and GMC Duramax Diesel Forum
11-16 LML Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #31 of 67 (permalink) Old 11-22-2019, 03:48 PM
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Quote:
Originally Posted by Collins View Post
I just discovered fast idle on my L5P last night.

Usually sleeps in the garage, but on a trip yesterday it sat out all day. 35F when I started it and it idled up to about 850 or so for about 10 minutes. Had the truck a year and never seen this before.

the high idle option is not listed on my build sheet and I have not made/changed any settings for this, so assume it is something built into all trucks, like the coil spring choke on a Rochester Quadrajet. (Ahh, the good old days...)
if you have rpo code -UF3 on build sheet
that's the high idle which is activated by pushing cruise button with truck in park .. ebrake on
designed for pto use on trucks.. takes rev's up to about 1200

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Last edited by Duramaxdan59; 11-22-2019 at 03:50 PM.
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post #32 of 67 (permalink) Old 11-22-2019, 06:12 PM
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Quote:
Originally Posted by sambor View Post
Good for you on the rpm. 3 of mine were 900-950. And as for required criteria- reread my post
Wow, you're a real contributor to the thread. Blocked.

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Last edited by SheeB; 11-23-2019 at 07:35 AM.
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post #33 of 67 (permalink) Old 11-22-2019, 09:12 PM
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Engine Idle Variations this refers to idle speed variations that are not caused by 'Elevated Idle' or Fast Idle' functions

Under certain conditions the engine
idle speed can vary or be elevated.
Change in idle speed is normal and
does not indicate a problem. Normal
conditions that can raise idle speed
are low voltage, DPF regeneration,
air conditioning compressor loads,
and engine warmup. These speeds
can range from approximately 600
to 1000 rpm.


Elevated Idle this is the one that is standard on dmax

The engine has a cold temperature
high idle feature which elevates the
engine idle speed from base idle to
1050 rpm for pickup models or
1200 rpm for van models when
outside temperatures are below
0C (32F), and the engine coolant
temperature is below 65C (150F).
This feature enhances heater
performance by raising the engine
coolant temperature faster. For truck
models, there may be two methods
of activating the elevated idle.
To turn this feature on or off:
1. Turn the ignition to ON/RUN,
with the vehicle off.
2. Press the accelerator pedal to
the floor and hold while quickly
pressing the brake pedal three
times in less than eight seconds.
3. Release the accelerator pedal
and start the engine.
If this method is not available, see
the alternate method under Truck
Models in Vehicle Personalization
(Truck Models)

When the engine is started, it will
slowly ramp up to the high idle
speed after a delay of a few
seconds up to approximately
two minutes. For this method to
work properly there must be no
throttle or brake pedal faults.
The engine idle speed will return to
normal once the following conditions
are met:
. Engine coolant temperature
reaches 65C (150F).
. Air intake temperature reaches
0C (32F).
The high idle speed will be
temporarily interrupted and the
engine speed will return to normal if
any of the following conditions
occur:
. The brake pedal is applied.
. The accelerator pedal is
pressed.
. The transmission is shifted out
of P (Park) or N (Neutral).
. Vehicle speed is detected.
Once these inputs are removed, the
engine idle speed will slowly ramp
back up to high idle after the normal
delay, if the conditions for engine
coolant temperature and air intake
temperature are still met.


Fast Idle Control this is the one that is there if the UF3 option is purchased sometimes called 'high idle'

The vehicle may have this system
which can be used to increase the
engine idle speed.
Fast Idle control will be enabled
when the following conditions
are met:
. The parking brake is set.
. The transmission is in P (Park)
or N (Neutral).
. The vehicle speed is about
0 km/h (0 mph).
. The cruise control Set switch is
pressed and released for Preset
Fast Idle Speed (1200 rpm).
Fast Idle control will be disabled
when one or more of the following
conditions occur:
. The cruise control Set switch is
pressed and released. See
Cruise Control in the owner
manual.
. The cruise control Cancel switch
is pressed.
. The brake pedal is pressed.
. The transmission is shifted out
of P (Park) or N (Neutral).
. The parking brake is released.
. The vehicle speed is not
0 km/h (0 mph).
On vans, when fast idle is active, a
FAST IDLE ON message will be
displayed in the DIC.
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post #34 of 67 (permalink) Old 11-22-2019, 10:35 PM
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I have a 2013 lml and I let it do what it wants when it's cold out. Lol I start it from the bedroom and get ready for work and when I go out its ready to rock and roll I just rolled 70k and no problems with the high idle I figure it's just powering the glow plugs and intake air heater and trying to get that alternator warmed up so I can do its job but I wouldn't worry about it. My grandfather always said if it's not broke dont fix it
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post #35 of 67 (permalink) Old 11-23-2019, 07:27 AM
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At 32 degrees, a minute or two is all I let it run before backing out and taking off. Now at -53, you better believe its gonna idle for the full 20 minutes that it will on the remote start before I go hop in it lol. Ive had it be so cold that the trans wont go into gear until its ran long enough to warm up some.
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post #36 of 67 (permalink) Old 11-23-2019, 07:37 AM
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Duramax Dan
The high idle is RPO UF3 like redwngr stated. It has only one speed--1000 rpm on trucks. The upspeed on PTO trucks( almost all WT's/ cab and chassis) is 3 different speeds: 900/1200/1900. Last 2 3500's and current 4500 have had this system. If you want to verify the info look at tech bulletin 120F on upfitters site.

By the way, the high idle speed UF3 on anything other than a van is 1000 rpm not 1200. That is the speed for vans.

Guess we have beat this thread to death-- at least until next cold season and new owners didn't get an owners manual.

By the way redwngr, can you edit your post to include the PTO speed info and sticky note it for future use? People seem to confuse elevated idle with high/fast idle

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post #37 of 67 (permalink) Old 11-23-2019, 08:01 AM
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My high idle on my 18 with is 1200. But it was added after purchase.
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post #38 of 67 (permalink) Old 11-23-2019, 09:36 AM
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Quote:
Originally Posted by MIkey52 View Post
My high idle on my 18 with is 1200. But it was added after purchase.
Yup.

That's an example of the UF3 'Fast Idle' that is operated by the cruise control buttons.
Factory installed UF3 should also be 1200 if in a pickup.

Elevated idle 1050 on pickups, 1200 on vans).

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Last edited by redwngr; 11-23-2019 at 09:55 AM.
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post #39 of 67 (permalink) Old 11-23-2019, 09:52 AM
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Quote:
Originally Posted by sambor View Post
Duramax Dan
The high idle is RPO UF3 like redwngr stated. It has only one speed--1000 rpm on trucks. The upspeed on PTO trucks( almost all WT's/ cab and chassis) is 3 different speeds: 900/1200/1900. Last 2 3500's and current 4500 have had this system. If you want to verify the info look at tech bulletin 120F on upfitters site.

By the way, the high idle speed UF3 on anything other than a van is 1000 rpm not 1200. That is the speed for vans.

Guess we have beat this thread to death-- at least until next cold season and new owners didn't get an owners manual.

By the way redwngr, can you edit your post to include the PTO speed info and sticky note it for future use? People seem to confuse elevated idle with high/fast idle
Fwiw, my post above is cut/past from the 2015 dmax supplement.

The confusion is why I copied the instructions for both 'elevated idle' and 'high/fast idle' in one post above.
Elevated idle is the one that is for cold weather engine/transmission warm up.


PTO operation is 10 pages of text and tables of info in the Dmax Supplement.
It's usage will be dependant on the PTO accessory that has been added.

Here is a link to the 40 page Bulletin at the gmupfitter site regarding the PTO for anyone that has one and needs more information.
https://www.gmupfitter.com/files/med...-2018DEC21.pdf

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post #40 of 67 (permalink) Old 11-23-2019, 07:22 PM
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Thank you for posting the info. It is a long procedure but the basics are similar to the high idle except for the 3 speeds

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