As GM Authority has covered previously, certain 2021 GMC Sierra 1500 models normally equipped with automatic engine stop-start are rolling off the line without the feature due to the ongoing global microchip shortage. The question is, how does the lack of automatic engine stop-start affect the 2021 GMC Sierra 1500’s fuel economy? To find out, GM Authority is pulling the specs and lining them up for comparison.
Per a statement from General Motors, most GMC Sierra 1500 models equipped with a V8 engine and 10-speed automatic transmission (RPO code MQB) produced on or after June 7th, 2021 will not be equipped with automatic engine stop-start. This includes 2021 GMC Sierra 1500 SLT models with the naturally aspirated 6.2L V8 L87 and naturally aspirated 5.3L V8 L84, as well as AT4 and Denali trims equipped with either the 5.3L V8 or 6.2L V8.
Automatic engine stop-start is designed to increase fuel economy and lower emissions by automatically shutting off the engine when a vehicle comes to a stop, such as at a stop light or in heavy traffic. When the driver removes their foot from the brake, the engine automatically restarts, allowing the vehicle to move forward.
To note, while some 2021 GMC Sierra 1500 models may not come equipped with automatic engine stop-start, they may still come equipped with other fuel-saving technologies, such as Dynamic Fuel Management (DFM) or Active Fuel Management. Both technologies deactivate engine cylinders under light driving conditions, improving fuel economy. However, as GM Authority covered in the past, the microchip shortage has affected the availability of these technologies as well, with some GMC Sierra 1500 pickups that would normally be equipped with AFM /DFM produced without the features. GM is offering a $50 credit on models that would normally offer the systems.
| Trim Level | Drivetrain | Engine | Transmission | Auto Stop/Start | Cylinder Deactivation | City mpg | Highway mpg | Combined mpg | Effective Date |
|---|---|---|---|---|---|---|---|---|---|
| All | 2WD | Turbo 2.7L I4 L3B | 8-speed auto | Yes | AFM | 20 | 23 | 21 | Start of 2021 MY |
| Base | 4WD | Turbo 2.7L I4 L3B | 8-speed auto | Yes | AFM | 18 | 20 | 19 | Start of 2021 MY |
| All | 4WD | Turbo 2.7L I4 L3B | 8-speed auto | Yes | AFM | 18 | 21 | 19 | Start of 2021 MY |
| All | 2WD | 4.3L V6 LV3 | 6-speed auto | No | AFM | 16 | 21 | 17 | Start of 2021 MY |
| All | 4WD | 4.3L V6 LV3 | 6-speed auto | No | AFM | 15 | 20 | 17 | Start of 2021 MY |
| All | 2WD | 5.3L V8 L82 | 6-speed auto | No | AFM | 15 | 21 | 17 | Start of 2021 MY |
| All | 2WD | 5.3L V8 L82 FFV | 6-speed auto | No | AFM | 15 | 19 | 16 | Start of 2021 MY |
| All | 2WD | 5.3L V8 L82 | 6-speed auto | No | No | 14 | 21 | 16 | March 22, 2021 |
| All | 4WD | 5.3L V8 L82 | 6-speed auto | No | AFM | 15 | 20 | 17 | Start of 2021 MY |
| All | 4WD | 5.3L V8 L82 | 6-speed auto | No | No | 14 | 20 | 16 | March 22, 2021 |
| All | 4WD | 5.3L V8 L82 FFV | 6-speed auto | No | AFM | 14 | 18 | 16 | Start of 2021 MY |
| AT4 | 4WD | 5.3L V6 L82 | 6-speed auto | No | AFM | 14 | 18 | 16 | Start of 2021 MY |
| All | 2WD | 5.3L V8 L84 | 8-speed auto | Yes | DFM | 17 | 23 | 19 | Start of 2021 MY |
| All | 2WD | 5.3L V8 L84 | 8-speed auto | Yes | No | 15 | 22 | 17 | March 22, 2021 |
| All | 4WD | 5.3L V8 L84 | 8-speed auto | Yes | DFM | 16 | 21 | 18 | Start of 2021 MY |
| All | 4WD | 5.3L V8 L84 | 8-speed auto | Yes | No | 14 | 20 | 16 | March 22, 2021 |
| AT4 | 4WD | 5.3L V8 L84 | 8-speed auto | Yes | DFM | 16 | 21 | 18 | Start of 2021 MY |
| AT4 | 4WD | 5.3L V8 L84 | 8-speed auto | Yes | No | 14 | 20 | 16 | March 22, 2021 |
| All | 4WD | 5.3L V8 L84 | 10-speed auto | Yes | DFM | 16 | 22 | 19 | Start of 2021 MY |
| All | 4WD | 5.3L V8 L84 | 10-speed auto | No | DFM | 15 | 21 | 18 | June 7, 2021 |
| AT4 | 4WD | 5.3L V8 L84 | 10-speed auto | Yes | DFM | 16 | 21 | 18 | Start of 2021 MY |
| AT4 | 4WD | 5.3L V8 L84 | 10-speed auto | No | DFM | 15 | 21 | 17 | June 7, 2021 |
| All | 4WD | 6.2L V8 L87 | 10-speed auto | Yes | DFM | 16 | 20 | 17 | Start of 2021 MY |
| All | 4WD | 6.2L V8 L87 | 10-speed auto | No | DFM | 15 | 20 | 16 | June 7, 2021 |
| AT4 | 4WD | 6.2L V8 L87 | 10-speed auto | Yes | DFM | 15 | 19 | 17 | Start of 2021 MY |
| AT4 | 4WD | 6.2L V8 L87 | 10-speed auto | No | DFM | 14 | 19 | 16 | June 7, 2021 |
| All | 2WD | Turbodiesel 3.0L I6 LM2 | 10-speed auto | Yes | No | 23 | 30 | 26 | Start of 2021 MY |
| All | 4WD | Turbodiesel 3.0L I6 LM2 | 10-speed auto | Yes | No | 22 | 26 | 24 | Start of 2021 MY |
| AT4 | 4WD | Turbodiesel 3.0L I6 LM2 | 10-speed auto | Yes | No | 22 | 26 | 24 | Start of 2021 MY |
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Comments
Auto stop and AFM have little effect on MPG.
But it does contribute to off cycle credits that help automakers meet regulations. These systems can not be tested to a regular cycle so the EPA assigns credits. These can get figured into the ratings. Mileage may vary in the real world.
Hehe!
Uk why is the 2.7 liter turbo wonder rated for such piss poor MPG in the Sierra vs the Silverado? Is this a typo? How can this engine possibly be rated for only 20 highway with 4WD and the 5.3 rates 22? This makes zero sense and must be a typo. Note that is rates the same in 2WD form so this has to be a mistake.
It’s a base level engine dude…
It’s not a mistake. I remember last year watching the “Engineering Explained” video and he kind of joked about how its mileage was actually worse than the 5.3L on the highway.
Can someone explain to me how start-stop effects highway mpg?
Good for starter sales.
Saves me from having to turn it off anyway. I disabled AFM on my Yukon Denali and I think I lost 2 tenths of a mpg. Well worth to extend the life of the motor and get rid of the 4 Cylinder drone.
Get rid of the start stop , its crap and I turn mine off as soon as I get in anyway. For what you save on fuel is a joke compared to the wear on a starter if your a city driver, as for the environment these vehicles today are clean so I wouldn’t worry about that. Go after India and China if you want to worry about the air quality
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Dang, if only the designers and engineers thought of this and there was the ability to beef up and put a strong starter motor on these things that wouldn’t be a problem. Oh wait, they did think of that and the starting system was strengthened to handle this. It is a non issue, it isn’t going to fail in 3-4 years they will last a long time; all that was considered when knowing and designing the system to not just start once per drive but many times per drive. People need to think and maybe do a little research before speaking with their antiquated ideas…
I’ve always said the stop/start system is hard on starters and other major engine components. GM needs to offer existing customers a free option to have it removed. Will GM pay for any and all future damages created by the start/stop feature? Doubt it!! When I remember, I too press the button to turn it off…needs to go folks.
Dang, if only the designers and engineers thought of this and there was the ability to beef up and put a strong starter motor on these things that wouldn’t be a problem. Oh wait, they did think of that and the starting system was strengthened to handle this. It is a non issue, it isn’t going to fail in 3-4 years they will last a long time; all that was considered when knowing and designing the system to not just start once per drive but many times per drive. People need to think and maybe do a little research before speaking with their antiquated ideas…
FYI, there is no added wear as oils coat everything just fine and not causing wear on restart as the engine is already warm. The cost savings alone covers any battery replacements but those also last a much longer time. Starters are beefed up and will last as long as a normal starter. Just enjoy the cost savings you are getting. That $100 a year roughly (it has been independently tested numerous times to save 5-8% of fuel in city driving) you are saving can cover any additional repairs and cover you for a few nice steak dinners a year.
Yes, they put a lot of effort into engineering the system to make sure it does a good job of doing something nobody actually wants their car to do.
Personally, I still wouldn’t buy a car that uses the starter motor for stop-start though.
My wife has a Wrangler that uses the motor-generator instead, and it is fast and quiet about restarting the engine. The main starter motor is only used when you actually start the car yourself.
I trust that a lot more.
I have a 21 Denali pick up. I despise this feature. It’s annoying and does nothing for gas milage from what I can tell. Most times at a red light, you take you foot off the gas at some point, and it restarts for the duration of time stopped anyway. You can shut it off,, but have to do so each time you start the vehicle. I just see this as an issue at sometime in the life of the vehicle