Is it just me (or a faulty thermostat) or does it take forever for the LMM to warm up. I can remote start it when it's 20 degrees out side, it will shut down after 10 minutes, I restart and wait about another 5-10 minutes get in and the temp gauge has not moved and the heater is ice cold.
What's up with this?
My other past deisels (PSD) warmed up in 5 minutes and had zero over heating problems.

Do I have a problem or is this just a poor engineering blunder?

Thanks,
Dave

Not sure, I remote start mine all the time, let it 'warm up' 5-7m, then jump in. Although the dials haven't moved much at all, by the time I get about 2-3 miles from the house, it's already starting to warm up, BUT, I use the upper winter cover. Keep in mind that when you remote start, until you put your key in the ignition, the AUTO and fan settings won't start 'doing their thing'.

Thanks TRMN8R...
However, when I remote start and the temp outside is cold, all my heating functions run on high including the heated seats. Maybe just an LTZ feature.
Dave

I don't have the lux interior, just the top level cloth. Sounds like it's a lux feature? So, you're not getting heat at all with everything on high?

You're not the only one who wasn't getting heat. The auto temp functions work with the auto start (blower on high, heated seats on, etc)...but I've also got the LTZ trim. I just don't get heat because the temp guage hasn't moved. Some cold mornings (for Maryland so teens at coldest) even after warming up for 10 minutes on remote start..it was still another 10-15 minutes before I had any resemblance of heat. I got a winter cover and it made a big difference. She still doesn't warm up on remote start just sitting there, but she warms up a lot quicker once I start moving.

You might have a problem. I have the 2008 LTZ with leather and remote start. When our temps were low, I would remote start mine. When I would get in, 5-10 minutes later, the seat warmers were on high, and warm, the defrost was on and the heater was on. When I would put the key in the guages would jump up, including the temp guage to at least half way to normal. And the seat heaters were really hot.
Sounds like a thermostat problem.

Is it just me (or a faulty thermostat) or does it take forever for the LMM to warm up. I can remote start it when it's 20 degrees out side, it will shut down after 10 minutes, I restart and wait about another 5-10 minutes get in and the temp gauge has not moved and the heater is ice cold.
What's up with this?
My other past deisels (PSD) warmed up in 5 minutes and had zero over heating problems.

Do I have a problem or is this just a poor engineering blunder?

Thanks,
Dave

It's a diesel...........at normal idle, it'll take forever to warm up. It it was getting warm in 10 minutes, then you'd have something to worry about. Every diesel I ever had was the same way. You can set the elevated idle and it'll warm up faster. Under 20 degrees.......I've found either: normal idle about 10 minutes, and then drive about 3 miles.........and you'll have hot air........., elevated idle for 10 minutes then drive about 1 mile.....and you'll have hot air, or just get in and drive and in about 5 miles you'll have hot air.

Now, if you have the climate system and you remote start.........in cold weather it should turn on the defroster. It'll start defrosting heavy frost in about 3 to 5 minutes..........it isn't blowing "warm" air, but it's warm enough to start making a dent. If you want to be warm immediately, you pretty much have to have the heated seats.

You might have a problem. I have the 2008 LTZ with leather and remote start. When our temps were low, I would remote start mine. When I would get in, 5-10 minutes later, the seat warmers were on high, and warm, the defrost was on and the heater was on. When I would put the key in the guages would jump up, including the temp guage to at least half way to normal. And the seat heaters were really hot.
Sounds like a thermostat problem.

x2

This is how my LTZ behaves as well. I would bring it in and have that t-stat checked...

My heater seems to heat up after 5 to 10 minutes of running. But not much up to you, I'm in socal and the temp is 45 to 50 in the mornings. You could always move to a warmer climate.:D

I dont have the auto temp feature, or heated seats. But when I start my LMM, she is blowing warm air in 4-6 min. Thats with temps in the teens.
Not hot air, but when i get in the temp gage is about half way to normal.
I have the high idle on, and never used the winter front.

Turn on the high idle feature. Put the accelerator to the floor and tap the brake 3 times with the key in the on.

I think I remember reading in the owners manual somewhere that your heater, heated seats, or air conditioning will only turn on if the outside temperature is either below a certain temp or above a certain temp for the a/c. I think it's something like 40 degree for the heater/heated seats.

I agree...with this being my first diesel I've noticed it takes a whole lot longer than any gasser I've had to warm up...I think it's just one of those "diesel things"...nothing out of the normal though :)

I won't claim to know the intricacies of the LTZ w/remote start but warm for 3 to 5 minutes then drive and the heat will come on in 3 to 5 more minutes. Idling in my opinion is a waste of fuel! That and the winter cover is your friend. You will learn that, trust me.

Turn on the high idle feature. Put the accelerator to the floor and tap the brake 3 times with the key in the on.


Bingo. Uses a bit more fuel, for the MPG folks, but it does make heat damm fast.

Diesels that are not under load don't warm up. So letting it idle does little/nothing. My CTD would cool off if I left it running (wife in truck) to run in to service the driver.

The high idle feature not only raises the idle but also closes the VGT turbo more than normal generating some backpressure.

The Dmax is like a gasser compared to the CTD as far as cold weather goes.

Nature of the beast. We get the benefit of very low idle fuel consumption, but if your not burning any fuel, your not making any heat. Just the design of the diesel. Do yourself and your truck a favor, plug it in. Plug the block heater in on a timer. 2-3 hours before you leave in the morning. Costs pennies in electricity, will save dollars in fuel and engine wear. -Murph

Our dealer told us the the heated seats work work on our truck unless the seatbelt is fastened?? I haven't tried it without, so I am not sure.

Turn on High Idle if you have that feature and I believe you can adjust the length of time before the vehicle will shut-off from remote-start to longer than 10 minutes. At least on my LMM you can.

i thought when you plug it in with the block heater it has to be at or below 0 for it to turn on thats what the plug and owners manual says but not to sure have not tried to use the block heat just turned on high idle and its warm in about 10min even on the cold mornings when its in the neg

...and I believe you can adjust the length of time before the vehicle will shut-off from remote-start to longer than 10 minutes. At least on my LMM you can.

I'd like to know how to do that...

Yup...takes a while to warm up but then so did my Dodge! I thought it was "normal" for diesels!

Turn on High Idle if you have that feature and I believe you can adjust the length of time before the vehicle will shut-off from remote-start to longer than 10 minutes. At least on my LMM you can.

I'd like to know how to do that...

I've read both my manuals cover to cover, and I know my LMM won't do that...

I've read both my manuals cover to cover, and I know my LMM won't do that...

Mine either - that's why I asked. Don't think it can be done with the stock system.

Well the 03 had to go quite a while before I would get significant heat, but the 08 I just jump in go - got the remote start, but a nusance to use , I just get in, make sure I have oil pressure and down the road I go. within 3 miles I have heat which is a big surprise compared to the older truck.

Is it just me (or a faulty thermostat) or does it take forever for the LMM to warm up. I can remote start it when it's 20 degrees out side, it will shut down after 10 minutes, I restart and wait about another 5-10 minutes get in and the temp gauge has not moved and the heater is ice cold.
What's up with this?
My other past deisels (PSD) warmed up in 5 minutes and had zero over heating problems.

Do I have a problem or is this just a poor engineering blunder?

Thanks,
Dave

I’m having a similar situation (lather LT, and remote start)…the problem is that last winter it worked perfect.
5 to 10 minutes warm-up was enough to warm it up to 70-80 degrees. If I put it in manual, it will blow hot air, but if it is in AUTO only the side vents are working and not very hot. I know the blower work and also the heat, but not in AUTO.
Any ideas of what is happening?

when i remote start my lmm, in ten minutes of running my seats are nice and toasty and the heater is blowing enough heat to be comfortable, mind you, I have my high idle switched to the on position.

I’m having a similar situation (lather LT, and remote start)…the problem is that last winter it worked perfect.
5 to 10 minutes warm-up was enough to warm it up to 70-80 degrees. If I put it in manual, it will blow hot air, but if it is in AUTO only the side vents are working and not very hot. I know the blower work and also the heat, but not in AUTO.
Any ideas of what is happening?\

I would imagine in the AUTO setting it won't come on untill it's warm enough to come on. In the MANUAL setting it will come on and blow cooler air untill it slowly starts blowing warm, then hot air.

Turn on the high idle feature. Put the accelerator to the floor and tap the brake 3 times with the key in the on.

Since the OP has an 07.5 LTZ, it would probably be easier to enable the high idle on the DIC. But I agree that's probably the problem. Although a diesel idling for 10 minutes will not be as warm as a gas engine idling for 10 minutes.

x3

If I put it in manual, it will blow hot air, but if it is in AUTO only the side vents are working and not very hot. I know the blower work and also the heat, but not in AUTO.
Any ideas of what is happening?

In Auto it will not start blowing until water temp is hot enough to provide the temp being requested.

Related Q; I'm sitting at a light, notice the temp gauge is at 210, and it's idling high, it's 45* out, the truck had been running for about 10 minutes, coolant is good and at the proper level, heat output has always been normal,

thoughts? thx.

In Auto it will not start blowing until water temp is hot enough to provide the temp being requested.

But it is hot enough to blow on MANUAL....?

I found the answer...this is normal operation.
Document ID: 1670833


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Air Delivery Description and Operation

The air delivery description and operation is divided into 7 areas:

•
HVAC Control Components




•
Air Speed




•
Auxiliary Air Speed




•
Air Delivery




•
Auxiliary Air Delivery




•
Recirculation Operation




•
Automatic Operation



HVAC Control Components


HVAC Control Module
The HVAC control module is a GMLAN device that interfaces between the operator and the HVAC system to maintain air temperature and distribution settings. The battery positive voltage circuit provides power that the control module uses for keep alive memory (KAM). If the battery positive voltage circuit loses power, all HVAC DTCs and settings will be erased from KAM. The body control module (BCM), which is the vehicle mode master, provides a device on signal. The control module supports the following features:

Feature
Availability

Afterblow
Yes

Purge
No

Personalization
No

Actuator Calibration
Yes


Auxiliary HVAC Control Module
The auxiliary HVAC control module is a GMLAN device that receives analog Inputs from the front HVAC control assembly and GMLAN message inputs from the rear seat audio (RSA) control module to maintain auxiliary air temperature and auxiliary air distribution settings. The battery positive voltage circuit provides power that the control module uses for KAM. If the battery positive voltage circuit loses power, all auxiliary HVAC DTCs and settings will be erased from KAM. The auxiliary HVAC control module will perform a recalibration of the electric actuators when commanded with a scan tool or if KAM is lost. This will ensure the actuators are moving with in the calibrated range.

RSA Control Module
The RSA Control Module is a GMLAN device that interfaces between the rear seat passengers and the auxiliary HVAC control module. The battery positive voltage circuit provides power that the control module uses for KAM. Air temperature, blower motor and air delivery rocker type switches are located on the face of the module.

These switches enable the module to send a GMLAN serial data message to the auxiliary HVAC control module for the change request. The module does not store auxiliary HVAC DTCs.

Mode Actuator
The mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts.

The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Auxiliary Mode Actuator
The auxiliary mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Ignition 3 voltage, low reference, control, 5-volt reference and position signal circuits enable the actuator to operate. The control circuit uses either a 0, 2.5 or 5-volt signal to command the actuator movement. When the actuator is at rest, the control circuit value is 2.5 volts. A 0 or 5-volt control signal commands the actuator movement in opposite directions. When the actuator shaft rotates, the potentiometers adjustable contact changes the door position signal between 0-5 volts.

The auxiliary HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded, or targeted, value, the control signal is changed to either 0 or 5 volts depending upon the direction that the actuator needs to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module.

Once the position signal and the commanded value are the same, the module changes the control signal to 2.5 volts.

Blower Motor Control Processor
The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive and ground circuits enable the control module to operate. The HVAC control module provides a variable voltage to the blower motor control module to request the selected blower speed. The blower motor control module provides a pulse width modulation (PWM) signal to the blower motor in order to control the blower motor speed. The module supplies 12 volts to the blower motor through the blower motor voltage supply circuit.

Auxiliary Blower Motor Control Processor
The auxiliary blower motor control processor controls the speed of the blower motor by increasing or decreasing the voltage drop on the ground side of the auxiliary blower motor. The auxiliary HVAC control module or rear seat audio module (RSA) provides a voltage signal to the auxiliary blower motor control processor over the auxiliary blower motor speed control circuit. As the requested blower speed increases, the auxiliary HVAC control module or rear seat audio module (RSA) increases the amount of time that the speed signal is modulated to ground. As the requested blower speed decreases, the auxiliary HVAC control module or rear seat audio module (RSA) decreases the amount of time that the signal is modulated to ground.

Air Speed - Front Control
The blower control switch is integrated into the HVAC control module. The 2 rocker type switches provide the vehicle operator the ability to select several blower speeds. The HVAC control module uses a bar graph type display to indicate the selected blower speed. The blower motor control module is an interface between the HVAC control module and the blower motor. The blower motor speed control, battery positive and ground circuits enable the control module to operate. The HVAC control module provides a variable voltage to the blower motor control module to request the selected blower speed. The blower motor control module provides a pulse width modulation (PWM) signal to the blower motor in order to control the blower motor speed. The module supplies 12 volts to the blower motor through the blower motor voltage supply circuit. When the HVAC control module is operating in AUTO mode, the system automatically controls the blower speed. If an OnStar® call is initiated while the blower is in the high speed position the blower speed will be lowered to reduce background noise.

Air Speed - Auxiliary
A rocker type switch on the RSA control module provides the operator the ability to select several blower speeds. The RSA control module uses a bar graph to indicate the selected blower speed. The auxiliary blower motor control processor supplies a 5-volt reference to the auxiliary HVAC control module on the auxiliary blower motor speed control circuit. The auxiliary HVAC control module pulls the 5-volt reference low towards ground to provide a blower motor speed signal. As the voltage decreases the blower speed increases. Power and ground are provided to the auxiliary blower motor control processor through the battery positive voltage and ground circuits. The auxiliary HVAC control module can not request A/C operation from the powertrain control module (PCM).

Air Distribution
The HVAC control module controls the distribution of air by the use of a mode actuator. The modes that may be selected are:

•
Defrost




•
Defog




•
Panel




•
Bi-Level




•
Floor


The mode actuator is connected to the mode door by a cam type linkage system. Depending on the position of the door, air is directed through the HVAC module and distributed through various ducts leading to the outlets in the dash. If the HVAC control module detects a fault with the mode door the HVAC control module will try to drive the actuator for a predetermined amount of time, to defrost, which is the defaulted position for the mode door actuator. When the mode switch is placed in the defrost or defog positions the A/C is commanded on and the recirculation door is moved to the outside air position to help reduce window fogging. A/C is available in all modes and recirculation is only available in the panel and bi-level modes.

Mode Actuator
The mode actuator is an electronic stepper motor with feedback potentiometers. The HVAC control module sends signals to the mode door actuator through the mode door control circuit. Zero volts drive the actuator in one direction while 5 volts move the actuator in the opposite direction. When the actuator receives 2.5 volts, the actuator rotation stops. A 5-volt reference signal is sent out over the 5-volt reference circuit to the mode actuator. When you select a desired mode setting, logic determines the value of the mode actuator signals. The HVAC control modules software uses this reference voltage in order to determine the position of the mode actuator through the mode door position signal circuit. The motor moves the mode door to the desired position.

Front Defrost
When defrost is selected, the A/C compressor is activated. The A/C compressor clutch will engage when ambient temperatures are above 3°C (38 F). The blower motor will be activated, regardless of the coolant temperature. The HVAC control module will override the auxiliary HVAC control module so a high volume of air is delivered to the front defrost vents. The rear window defogger does not affect the HVAC system.

Air Distribution - Auxiliary Control
The auxiliary HVAC system provides ventilation for the rear seat occupants. The rear seat occupants will exercise control of the auxiliary air delivery modes, air speed and air temperature setting.

When the auxiliary mode switch is toggled, a signal is sent to the auxiliary mode actuator through the auxiliary mode door control circuit. Power and ground are supplied to the auxiliary mode actuator through the ignition 3 voltage and ground circuits.

A rocker type switch on the RSA control module provides the operator the ability to select several blower speeds. The RSA control module uses a bar graph to indicate the selected blower speed.


Recirculation Operation


The HVAC control module controls the air intake through the recirculation actuator. The recirculation switch closes the recirculation door in order to circulate the air within the vehicle. The outside air switch opens the recirculation door in order to route outside air into the vehicle. Regardless of the blower motor switch position, recirculation is available only in the panel and bi-level mode switch positions. Including the OFF position. The mode switch must be placed in either the panel or bi-level position before the blower motor switch is placed in the OFF position. In order to reduce windshield fogging, outside air is circulated when the mode switch is in the defrost or defog positions. If the recirculation switch is pressed into the ON position when the mode switch is in an unavailable mode position, then the recirculation switch LED will flash 3 times. If the HVAC control module detects a fault with the recirc door the HVAC control module will try to drive the actuator for a predetermined amount of time, to outside air, which is the defaulted position for the recirculation actuator.


Automatic Operation


In automatic operation, the HVAC control module will maintain the comfort level inside of the vehicle by controlling the A/C compressor clutch, the blower motor, the air temperature actuators, mode actuator and circulation.

To place the HVAC system in Automatic mode, the following is required:

•
The Auto switch must be activated




•
The air temperature switch must be in any other position other than full hot or full cold position


Once the desired temperature is reached, the blower motor, mode, recirculation and temperature actuators will automatically be adjusted to maintain the temperature selected. The HVAC control module performs the following functions to maintain the desired air temperature:

Monitor the following sensors:

•
Inside Air Temperature Sensor




•
Ambient Air Temperature Sensor




•
Lower Left Air Temperature Sensor




•
Lower Right Air Temperature Sensor




•
Upper Left Air Temperature Sensor




•
Upper Right Air Temperature Sensor




-
Regulate blower motor speed




-
Position the air temperature actuator




-
Position the mode actuator




-
Position the recirculation actuator




-
Request A/C operation



Remote Start


Remote Start Activation
The following describes the HVAC control head functionality upon receiving the remote start active serial data message and a power mode status is set to off/awake. The outside air temperature (OAT) sensor on automatic systems, is utilized to determine the moding of the following features: Blower Mode, Bi-level, Floor, Defrost, Recirc and Rear Defrost. Calibratable temperatures are utilized to provide low, mid and high temperature ranges for the selectable feature. Blower and mode have the range to select any valid feature positions. When the remote start active serial data is received, ignition-OFF loop HVAC algorithms will act the same as if a run power mode was received, i.e. re-calibration, afterblow, ignition-OFF motor positioning etc. The OFF timer and the ignition ON timer have the functionality as in the Run mode.

The remote start system operates in one of three zones of operation:

•
Cold ambient temperature that is below 5°C (40°F)




•
Hot ambient temperature that is above 30°C (86°F)




•
Mid ambient temperature that is anything between the cold and hot values




•
In cold ambient, the system uses 74°F setpoint , auto blower, defrost mode, rear defrost and/or heated mirrors on, heated seats on, rear in mimic.




•
In mid ambient, the system uses 74°F setpoint, auto blower, auto mode, rear in mimic.




•
In hot ambient, the system uses 74°F setpoint (60°F setpoint in 2008), auto blower, auto mode, rear in mimic.


Remote Start De-activation
When the remote start is exited, GMLAN power mode equals run mode or remote start engine. In the case of automatic settings, the displays will revert to the actual state of operation of the features, on the basis of their normal control algorithms.

Related Q; I'm sitting at a light, notice the temp gauge is at 210, and it's idling high, it's 45* out, the truck had been running for about 10 minutes, coolant is good and at the proper level, heat output has always been normal,

thoughts? thx.

You may be in regen.