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Discussion Starter · #1 ·
So this LM2 has an exhaust brake but no switch. If am towing a boat down a steep highway grade how do I best keep her slowed down?
Thanks
 

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Discussion Starter · #3 ·
I thought I heard it only works when the cruize control is on.??
 

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From Diesel manual:

Exhaust braking is automatically activated when Tow/Haul Mode is selected. It maintains the vehicle’s speed by automatically implementing a shift pattern that uses the engine and the transmission to slow the vehicle. The system will command downshifts and use the turbocharger on the engine to reduce the vehicle’s speed when the brake is applied. The normal tow/haul shift pattern will return once the vehicle is on a low grade or when the accelerator pedal is pressed.

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Bet that info is in the owners manual?
 

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Discussion Starter · #7 ·
ok so tow/haul mode on and cruise control on. What do you do if it is still going to fast? If you hit the brakes then the cruise disengages and I assume so does the exhaust brake? Can you use the manual down shift and still get the exhaust brake to work?
With my '05 6.6 dmax there was no exhaust brake but in tow/haul the allison tranny would down shift when you pressed the brakes pretty hard and the two would keep me slowed down on those 7% grades in the smoky mountains.
I am towing a 4000 lb boat.
 

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I thought I heard it only works when the cruize control is on.??
On LM2 it is turned on with tow/haul.

It uses the set speed as an indicator of the maximum desired speed as well as the minimum.

When not in cruise, it will use brake tap as a signal that you don't want to go faster.
The more aggressive the brake application, the more aggressively it will help.

Fwiw, the 'exhaust brake switch' on the 6.6 does not 'apply' the exhaust brake but it 'enables' the exhaust brake -- which then activates similar to above.

Kinda like now cruise 'on' enables the system, and cruise 'set' activates it.
 

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Discussion Starter · #9 ·
ok great info. Thanks
 

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Since I've started towing my boat now that the weather is getting better, I've been playing with the tow/haul mode and exhaust brake. So far, the exhaust brake has not impressed me. The owner's manual is vague on it's usage.

Coming from the Colorado 2.8, the exhaust brake on the Silverado is nonexistent. On the Colorado, tapping the brakes resulted in downshifts and increased exhaust braking. Tapping the brakes on the Silverado 3.0 does nothing except kick out cruise (if activated). No downshift, no braking. Coming off the highway at 70, pressing and holding the brake only results in downshifts to the lower gears when coming to a stop. And when using Cruise, the Silverado will not hold a downhill speed. It downshifts fine but will run the RPMs up toward 4k while continuing to increase speed (cruise set at 65, speed increased to 70 before I applied the brakes to slow down). The Colorado exhaust brake was much more aggressive which is needed at times, helped normal stopping greatly and held downhill speeds pretty well.

Playing with the different modes, there is no difference in braking (IMO) between Normal, Sport and Tow/Haul modes. The downshift points appear to be the same with no decrease in stopping distance with Tow/Haul engaged. What am I missing?
 

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The exhaust braking on these trucks appears to be a function of the exhaust side of the turbo. In order to achieve the braking, the vanes on the exhaust side of the turbo flatten somewhat. It does not have the traditional baffle in the exhaust which some people are familiar with.
 

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I believe all duramax with factory exhaust work by closing off the Vvgt. Try a panic type stop some times and see how it does. I didn't think mine was doing much till I had a panic stop one day. It really worked. At 2200 rpm's and less it is not as near effective as it is at 4300rpm.
 

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Be wary to use it on slippery/icy roads.


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Indeed.

To expand on this, the force applied by the exhaust brake is only applied to the driven wheels, so for equivalent braking force applied by the service brakes (all wheels) versus the exhaust brake (driven wheels only), the applied force per wheel must be higher when using the exhaust brake. That means that you'll be pushing those wheels/tires much closer to their tractive limit than you realize.

Exhaust brake is great for controlling speed on long descents in good weather, as it will allow you to apply braking force without using up your service brakes' heat capacity. But on slippery surfaces it can put you into a drive-wheel skid.
 

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Thanks for the replies. Don’t necessarily want to panic stop, just get the exhaust brake to help slow down before stopping like the Colorado did. Guess that isn’t in the cards with this truck. It was nice being able to tap the brake twice to get it to downshift two gears. Not so with the 3.0.

I heard the exhaust brake was less aggressive but didn’t realize how much until I started towing more frequently. Be nice if GM had an update that would increase the braking rate.
 

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Thanks for the replies. Don’t necessarily want to panic stop, just get the exhaust brake to help slow down before stopping like the Colorado did. Guess that isn’t in the cards with this truck. It was nice being able to tap the brake twice to get it to downshift two gears. Not so with the 3.0.

I heard the exhaust brake was less aggressive but didn’t realize how much until I started towing more frequently. Be nice if GM had an update that would increase the braking rate.
Try applying the service brake for a few seconds with very light pressure. In my 3500 this will engage the exhaust brake even if the applied braking force is nominally zero; as long as I have the pedal depressed enough for the brake lights to be on, the exhaust brake logic clicks over and it does its thing, and will automatically downshift to bring the vehicle's speed down.

Alternatively, you can use it in combination with cruise control, which is really spectacular when pulling a trailer in mountainous areas. You can drive up and down huge grades without touching any pedals.
 

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Discussion Starter · #16 ·
sure wish we could get a GM engineer to reply to this. How is it SUPPOSED to work vs what users are understanding how it works.
 

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Mine works pretty much like the owners manual says. And JD is right. The longer foot is on pedal, along with how much pressure is applied the more aggressive the braking.

If you are cruising along and just tap the brake and let off, the trucks says ok the driver just wants to coast. Put on brake and keep it applied even so lightly and mine will downshift and vanes go 100% closed. The more aggressive my braking the more aggressive the downshifts.
 

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I believe all duramax with factory exhaust work by closing off the Vvgt. Try a panic type stop some times and see how it does. I didn't think mine was doing much till I had a panic stop one day. It really worked. At 2200 rpm's and less it is not as near effective as it is at 4300rpm.
FWIW, early dmax generations did not have exhaust brakes.
 
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