How to tell if engine heater is working?

[YukonDoItXL]

Just purchased a 2023 Yukon XL Denali Diesel. It's cold here, it took about 10-20 minutes for the car to warm up. I tried plugging the car in for a few hours, but the warm up time seemed to remain the same. Is there any way to determine if the engine heater is operating? I didn't see any lights on the dash showing its plugged in.

 

[Doubeleive]

Just purchased a 2023 Yukon XL Denali Diesel. It's cold here, it took about 10-20 minutes for the car to warm up. I tried plugging the car in for a few hours, but the warm up time seemed to remain the same. Is there any way to determine if the engine heater is operating? I didn't see any lights on the dash showing its plugged in.

laser thermometer, there cheap at harbor freight, walmart, etc.
it may be worth noting that they do not "turn on" until 0 deg. as far as I am aware.

 

[Stbentoak]

laser thermometer, there cheap at harbor freight, walmart, etc.
it may be worth noting that they do not "turn on" until 0 deg. as far as I am aware.

I don't think that's true. I think they have a thermostat built into them so they don't overheat anything, but they will heat even if the ambient temperature is 50 degrees out. It's just whether you are wasting your money or not plugging it in. I have it, but I have never plugged mine in once. This vehicle heats up faster than any I've ever seen due to the directional coolant valve. I used to have an old 5.9 Cummins. It took 1/2 an hour of driving to get it up to temperature in the winter. That vehicle really benefited from a block heater.

 

[Fless]

You could read the engine temp with a scanner before plugging in the heater, then let it run for a while to see if it works at your ambient temp. Like @Doubeleive noted, at least the older ones (like mine) don't seem to work -- or aren't needed -- until 0 deg F. Might be different on the diesels.

Your manual says essentially the same thing, but it's not clear if the heater works above that temp:

 

[Doubeleive]

all the data I have ever seen shows they do not turn on until it reaches 0 deg, it's a built in sensor inside the heater.

 

[Marky Dissod]

... at least the older ones (like mine) don't seem to work -- or aren't needed -- until 0F.
Might be different on the diesels.
Your manual says essentially the same thing, but it's not clear if the heater works above that temp ...

The engine heater can provide easier starting and better fuel economy during engine warmup in cold weather conditions at or below -18C / 0F.

Know for a fact that GM Gen3 V8s have a parameter that turns off the heater over a certain temp, or after a certain time interval - it IS tunable.
Although it's likely tunable in Gen4 & Gen5 V8s, if the definition file is not 'fully enabled', it may not show it to the end user.

Leaving the above error intact ...

 

[Fless]

Know for a fact that GM Gen3 V8s have a parameter that turns off the heater over a certain temp, or after a certain time interval - it IS tunable.
Although it's likely tunable in Gen4 & Gen5 V8s, if the definition file is not 'fully enabled', it may not show it to the end user.

I'm not sure about the Gen3 heaters in the SUVs. Mine's a 110v external plug-in with no electronic connection to the SUV. How would the SUV turn it off?

 

[Doubeleive]

Know for a fact that GM Gen3 V8s have a parameter that turns off the heater over a certain temp, or after a certain time interval - it IS tunable.
Although it's likely tunable in Gen4 & Gen5 V8s, if the definition file is not 'fully enabled', it may not show it to the end user.

nyet.....
operation is governed by a built-in thermostatic cord, and the vehicle's software monitors its impact on the engine sensors. Here is how the logic works on the current generation:

1. The Thermostatic Cord (The "Internal" Controller)​

The actual power flow is controlled by a thermostat integrated into the 110V power cord itself.

• Activation: The cord will only allow electricity to flow to the heating element when the ambient temperature is below 0°F (-18°C).
• Deactivation: Once the cord senses the temperature has risen above approximately 10°F to 15°F, it cuts the power.
• Software Implication: Even if you plug it in when it's 30°F outside, no electricity is being used because the cord’s hardware is blocking it.

2. Software Monitoring (The "Check Engine" Factor)​

While software doesn't "turn it on," the Engine Control Module (ECM) is very aware of the heater.

• Rationality Check: When you start the vehicle, the ECM compares the Intake Air Temperature (IAT) and the Engine Coolant Temperature (ECT).
• The Problem: If the block heater makes the coolant significantly warmer than the rest of the engine block in a way that doesn't match the software's "expected" map, it can sometimes trigger a Check Engine Light (CEL) for "Sensor Rationality."
• The Fix: GM’s software is programmed to ignore these temperature discrepancies only if it detects that the temperatures are within a specific range consistent with block heater use.

3. Remote Start Integration​

The vehicle software does manage the climate and engine behavior differently if it's cold:

• If you use the MyGMC App or the key fob to remote start, the software ignores the block heater's "fake" heat and continues to run the high-idle warm-up cycle until the engine reaches operating temperature.

Important Note for 2024 Owners:​

If you are trying to "force" the heater to run at 20°F (which many owners prefer for a faster cabin warm-up), you cannot do this through a software setting. The only way to bypass the software/hardware restriction is to:

1. Replace the cord with a non-thermostatic aftermarket version (not recommended, as this can trigger the Check Engine Light mentioned above).
2. Use an external timer on your garage outlet, though the cord's internal thermostat will still likely prevent it from drawing power unless it hits that 0°F threshold.

Summary: You won't find an "Enable Block Heater" button in your Yukon's settings. It is an automated system that relies on a temperature-sensitive cord, which the engine's software simply "tolerates" rather than controls.

 

[Marky Dissod]

There is no simple 'Enable Block Heater' switch setting, what I'm thinking of is a set of mathematical variables. I'll do more research on this. ...

 

[Doubeleive]

There is no simple 'Enable Block Heater' switch setting, what I'm thinking of is a set of mathematical variables. I'll do more research on this. ...

there is no physical connection from the heater to the ecm/bcm, it's a dumb thermistor switch in the electrical cable

 

[B-train]

Generators have used these for years. There's no connection to anything PCM/BCM related. It's a temperature switch on the cord itself. Feedback is either through a direct contact temperature sensor with the coolant, or a proximity sensor for radiated temperature of the block.

There are all sorts of little thermal switches you can get with varying on/off settings. But, for ease of use in different temperature ranges, I'd just cut the cord after the temp sensor, install a new cord that's longer, and use a wall mounted timer (similar to those for holiday lights, etc).

You could even use a generator cord setup. There are temp settings built in where it keeps the coolant in a certain range. Examples: ON at 100F, OFF at 120F (most common), or ON at 60F, OFF at 90F. This type could be left plugged in all night and would cycle as needed to stay in the range.

 

[JayceeP]

How cold? I find the diesel warms up pretty quick. But I haven’t started it colder than a -20C windchill.

 

[Stbentoak]

The only block heater I ever had was one that I manually installed. And when you plug it in, it ran. I see that these OEM ones are a little more sophisticated. Maybe a little too sophisticated. If I want to plug it in at 20 or 30 degrees outside, I want it to work. I would prefer that it could just be put on a timer. That's what really works the best. Have it start about three hours before you go to work in the morning. When you get in, you have warm oil and you have heat within about 30 seconds.