Diesel Exhaust Brake Operation

The diesel exhaust brake available on 2020 Silverado and Sierra light-duty and HD models equipped with the 3.0L Duramax diesel engine (RPO LM2) or 6.6L Duramax diesel engine (RPO L5P) enhances the vehicle brake system by using engine braking and automatically downshifting the transmission to help slow the vehicle. All of which can be helpful when towing or hauling heavy loads while also reducing brake wear. (Fig. 10)


Fig. 10


When the diesel exhaust brake is active, transmission downshifts may be automatically selected to increase engine speed, which increases the effectiveness of the exhaust brake. The number of downshifts selected is determined by the length of time the brakes are applied and the rate the vehicle is slowing. The system delivers the correct amount of braking to assist in vehicle control. The heavier the vehicle load, the more active the engine exhaust brake will be.

The system will not downshift the transmission if the vehicle is in Range Selection Mode (limits the transmission to the top gear selected and lower gears).

Activating the diesel exhaust brake system differs based on the engine.


3.0L Diesel Engine

The diesel exhaust brake function on the 3.0L diesel engine is part of the Tow/Haul Mode Grade Braking system. Tow/Haul Mode Grade Braking is only enabled while the Tow/Haul Mode is selected.

On vehicles equipped with Driver Mode Control, Tow/Haul Mode can be activated/deactivated by turning the Driver Mode knob to the left. (Fig. 11) When selected, the Tow/Haul Mode symbol will illuminate in the instrument cluster.


Fig. 11


If the vehicle is turned off with Tow/Haul Mode active for less than four hours, Tow/Haul will remain active after the vehicle has been turned on again. Otherwise, the vehicle will start in Normal Mode.

For vehicles without Driver Mode Control, press the Tow/Haul button on the center of the instrument panel.

TIP: The Automatic Engine Stop/Start system is unavailable when the Tow/Haul Mode is active.


6.6L Diesel Engine

The diesel exhaust brake is activated on vehicles with the 6.6L diesel engine by pressing the Diesel Exhaust Brake button on the center of the instrument panel. (Fig. 12) The button indicator will turn on when the exhaust brake is activated.

The exhaust brake will activate more often when the Tow/Haul Mode is selected.


Fig. 12


The diesel exhaust brake system will not remain active on the next ignition cycle. The instrument panel button must be pressed each time the vehicle is started for the system to be active.


– Thanks to Tim Pierce, Dave MacGillis, and Kevin Minor


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One Comment

  1. ed thomas says:

    on the 3.0l duramax, at what rpm does the engine brake become active?

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