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We purchased a 2020 GMC 2500 HD Denali upgrading from a 2017 Chevrolet 2500hd Duramax. On the 2017 when braking, we could hear and feel the engine exhaust brake. The new 2020 does not seem to decelerate in the same fashion. If the engine brake is not working on the 2020, would we get a check engine light? Thanks.
 

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The new engine brake works differently. The ECM controls how much engine braking is applied much more intelligently than on previous models. Are you in Tow/Haul mode when using the engine brake? Below is information posted in another thread that I think you'll find useful.


Exhaust Brake Feel During Operation
July 22, 2020
The enhanced exhaust brake is one of several improvements in 2020 Silverado and Sierra models equipped with the 6.6L Duramax diesel engine (RPO L5P). The exhaust brake feature can be used to provide additional braking when the vehicle is decelerating with a heavy load, and/or down a steep grade.
The exhaust brake system is activated using a driver-selected switch (Fig. 21) that provides an input to the BCM, which sends a request to the ECM. The ECM processes the request and controls exhaust brake operation based on various sensor inputs. The ECM commands the turbocharger vane position to maximum boost for exhaust brake operation.
Prior to the 2020 model year, the movement of the turbocharger vanes was very rapid and the engagement of the exhaust brake could be felt by the driver. For 2020, the movement of the vanes is slows, which can give the feeling that the exhaust brake is not operating correctly. As long as the Driver Information Center (DIC) message “Exhaust Brake On” is displayed and no DTCs are set, the vehicle is functioning properly.

Fig. 21

For additional customer information, refer to the following exhaust brake description from the Owner’s Manual:
  • Automatic downshifts will not occur if the vehicle is in Range Selection Mode.
  • The exhaust brake only activates when the transmission torque converter is locked. This can vary based on vehicle speed, gear, and load.
  • To activate the system, press the Exhaust Brake button on the center stack. A light in the switch will come on when the exhaust brake is activated. The switch must be pressed at each vehicle start for the system to be active. The DIC displays the message Exhaust Brake On for approximately three seconds, and then clears.
  • To turn the brake off, press the exhaust brake switch a second time. The DIC displays the message Exhaust Brake Off for approximately three seconds, and then clears.
  • The exhaust brake will be more active when in Tow/Haul Mode.
 
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