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How To Put A Semi-truck In High Idle? (Explained & Solved!)

Setting a semi-truck at high idle helps the engine to run smoothly.

When a semi-truck is in high idle, it improves the performance of other essential parts, such as increasing the oil pressure to provide better lubrication and giving more amperes to the alternator to keep the battery charged.

However, not all truckers know the importance of putting their semi-truck in high idle and the steps to do it.

In this article, you will learn more about the essentials of high-idle mode in semi-trucks and how to set it.

A Short Answer on How to Put a Truck in High Idle:

The simplest way to put your truck in high idle is by pressing down the fuel pedal. Then, ensure you set the cruise control to the ideal revolutions per minute range. In semi-trucks, it is typically around 900 to 1200 rpm. The settings are all quite similar among different semi-truck brands.

What RPM Should a Semi-truck Idle at?

The rpm settings among semi-trucks are almost the same. It only varies on the diesel engines used and the other specifications of the vehicle.

But, in general, when keeping a semi-truck idle, always ensure it is within the recommended setting of 900 to 1200 RPM or higher, depending on your semi-truck.

This rpm reading is enough to give the oil the correct pressure to reach the engine.

What is High Idle in a Semi-truck and When Should it be Used?

When in high idle, your vehicle is still operating even if it is disengaged with the engine.

When your semi-truck is in neutral or when parked, you should idle it to keep the engine running even if you do not drive.

That way, you can maintain the engine’s temperature and keep its performance when you go back to driving again.

At 900 to 1200 rpm, the semi-truck engine is already idling. You can increase the rpm depending on your semi-truck’s capacity.

How to Set High Idle on Freightliner?

As mentioned, setting high idle in semi-trucks is similar to different brands. But we will still give you the details to follow exactly what your semi-truck requires.

To set a Freightliner truck in high idle, you can start by toggling the parking brake. Ensure that your truck is in neutral and put it in the high range, especially if it is manual.

Toggle the cruise control using the on and off buttons. You will then see that the idle management light on the dashboard will start flashing. Depending on your Freightliner model, you can use the set or reset buttons to idle.

Now that the idle management light is already flashing, you can optimize it to high idle.

You will notice that the semi-truck is going to shut down. But since the idle management light is still on, you need to wait for a few minutes for it to prepare to idle by itself and turn to battery mode.

You can monitor the engine temperature, voltage, and other essential parameters when in battery mode.

Freightliner Cascadia High Idle

You can high idle a Freightliner Cascadia whether it is off or running. However, you still need to ensure that the key is in the ‘On” position.

You can do it by selecting it on the screen dashboard. Go to vehicle settings and select the engine idle adjust menu. Then you can choose optimized idle, which will also prompt you with a warning message. Just press ok.

Please also pay attention to the interior comfort menu. You can choose to turn it on or off.

When on, you can keep your semi-truck warm or cool since it allows you to control the HVAC system.

When off, the truck will turn to battery mode, which allows you to monitor the batteries, keep the batteries charged, and keep the engine fluids from freezing.

After that, you will see a green engine icon in the bottom left of the screen, indicating that the truck is in high idle.

Freightliner M2 High Idle

Turning the Freightliner M2 to high idle is similar to any Freightliner model.

All you need to do to start idling is to turn on the cruise control.

Turn the Freightliner M2 on using the cruise control. Tap and hold the brake to resume the engine and turn it to the recommended rpm for high idling.

How to Set High Idle on International?

When setting an International truck to high idle, you need to turn the cruise on.

After that, hold the accelerator or the resume switch. You need to wait up to five minutes to shut the engine off.

Once it is off, the engine of your International truck will start idling. You can then set it then to the ideal rpm for high idling.

How to Set High Idle on Kenworth?

Like any other semi-trucks on different brands, turning the Kenworth truck to high idle starts with turning the key into the off position. The dashboard screen will then turn blank.

Come over to the switch and hold it up. Keep holding it until the dashboard screen turns on.

Wait for a while, as the semi-truck will then conduct a quick check on several parameters, such as if the hood is closed or if your vehicle is in neutral mode.

After that, you will see the auto-start icon on the dashboard, and your truck is finally in idle mode. 

You can adjust the other controls as needed to maintain the temperature of your truck or keep the oil flowing to the engine.

How to Set High Idle on Cummins?

To enable high idle in a Cummins truck, you must ensure the key is on, and the engine is off.

Go to the GT main menu and select the special functions option. From there, you can enable high idle by turning it on.

Go back to the main gauge screen and turn the key off. You can do it by pulling the key out of the ignition.

Open the doors of the semi-truck to allow the electronics to power down. After doing that, you can finally confirm that you enabled high idle.

Now that it is all set, start the truck engine and turn on the cruise control.

Press the accelerate button to increase idle for the cruise control.

If you want to stop high idle, tap the brake, cancel the cruise button, or turn off the cruise.

How to High Idle a Mack Truck?

When turning a Mack truck to high idle, you must turn on cruise control. Then hold the accelerator button until they reach the desired RPM.

When high idling, the recommended RPM is above 1000.

If you cannot adjust the engine speed using the speed control switches, the function is not enabled in the VECU or the electronic control unit.

You may also need to use the PTT or premium tech tool to make parameter changes in the control module.

Mack Granite High Idle

When turning the high idle of a Mack Granite truck, you need to enable cruise control.

Then, put your foot on the pedal gas to slightly increase the engine. After that, hit set. From that point, the engine will stay on.

To high idle, adjust the rpm to 700 and gradually increase it to reach the recommended RPM for high idle.

How Long Should a Truck be on a High Idle?

The duration of turning your semi-truck to high idle varies among truck brands and manufacturers, but it can also be based on your discretion.

Some manufacturers recommend only a short warmup or cooldown period, primarily if you use your vehicle for a more extended period or have been under high-power operation.

However, since you are the vehicle owner or driver, you can understand better how long you should set it that way.

Generally, more than five minutes of idling is already too much for a semi-truck. Thus you should avoid doing it frequently.

The most recommended and acceptable is idling your vehicle for up to 30 seconds to one minute. You can ensure that it will not cause any harm to the engine of your semi-truck.

You can also check if your semi-truck is in the latest model and has equipped with advanced technology or setting that can allow your vehicle to idle longer than recommended and will not cause any damage to it.

If you keep exceeding high idle on your semi-truck, it can waste fuel and cause wear and tear to the engine.