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Chevrolet makes Stop/Start standard on base 4-cylinder in 2015 Impala; 5% improvement in city fuel economy

Stop/start technology will be standard on the 2015 Impala base 2.5-liter ECOTEC engine, an addition that improves the vehicle’s city fuel economy by nearly 5%, or one mile per gallon. The Impala comes standard with a four-cylinder engine, which currently accounts for more than 30% of Impala retail sales.

For the 2015 model year, the Impala will be available with two powertrains, a standard 2.5L engine with stop/start, and a premium 3.6L six-cylinder engine. The Impala with the 3.6L V-6 engine will not include stop/start technology.

Stop/start shuts down the engine in certain driving conditions to reduce fuel consumption. The technology is becoming more prevalent worldwide. A recent report from Navigant Research predicted worldwide sales of vehicles with stop/start technology (SSVs) will grow from 8.8 million in 2013 to 55.4 million in 2022. (Earlier post.)

The 2.5L Impala with stop/start yields an EPA-estimated fuel economy of 22 mpg city (10.7 l/100 km), 31 mpg (7.6 l/100 km) for the highway and 25 mpg (9.4 l/100 km) combined.

The Impala becomes the second vehicle in Chevrolet’s US. lineup to feature stop/start technology, following the segment-first standard inclusion in the 2014 Malibu introduced late last year. The technology helps improve the Malibu’s city fuel economy by 14%.

Chevrolet engineers developed the stop/start in the Impala from extensive experience with GM’s eAssist system and the accompanying algorithms that allow engines to engage and disengage subtly.

Stop/start system customer research indicates they want the engine to start up as quickly and smoothly as possible after a stop.

—Mark Meyers, Chevrolet Global Vehicle Performance manager

During the development of this technology, a team of software engineers was created. The Center for Excellence focuses on advancing stop/start technology and making its operation seamless to the customer.

A big challenge for the team was overcoming “change-of-mind events,” instances in which the driver begins to stop, but then quickly accelerates. The algorithms adapt the system so the starter can fire even if the engine did not fully shut off.

The software also prevents the system from engaging if the car does not reach 6 mph (10 km/h) since its last start—a feature for stop-and-go-driving conditions. The system also considers cabin temperature, humidity, battery charge and other factors when deciding if the engine should come to a stop.

Hardware revisions also have been made. The noise and vibration team worked closely with drivetrain engineers to revise motor mounts to provide the greatest isolation possible from the cabin. Additionally, the team included a larger heavy-duty starter motor to assist with the additional ignition cycles.

The 2015 Impala goes on sale this summer with a suggested starting price of $27,735 for the 4-cylinder LS model, and $30,960 for the 6-cylinder LT model. These include an $825 destination charge, but exclude tax, title, license and dealer fees.



Is it a lead acid battery? 48V? Who makes it, the battery?


Must be a great time to be an engineer at the car companies. It must be a breath of fresh air to actually work on drive train features.

Still, I won't touch a GM car. Too many pieces just break prematurely, and with them adding new things, it's just one more thing to break.

Hybrids don't have this issue with start stop as the software is already there with the help of an electric motor to take care of the indecision to actually stop or keep going.


I wonder why Bob Lutz didn't think of this?


Impala stop-start
Although this is a nice development, I am not too impressed by the “extensive experience” cited by GM themselves. I had the stop/start feature already in my previous BMW MY´2008 car (and I also have it on my current Ford). Systems today are probably somewhat more refined but it still looks like a copycat feature to me. To my knowledge, the “change-of-mind” feature was first introduced by Jaguar some years ago. All other features mentioned are also well-known. In summary, I cannot see any innovation in this, just the application of known technology a couple of years later that the forerunners.

TM, you are probably right about GM cars regarding premature breakdown in general. However, I would not fear start/stop systems and particularly not when it comes to software. The software here is much simpler than that for hybrid systems.

This is (most likely) not a 48V system and the battery is most certainly a lead-acid battery of the type that has been developed for start/stop systems by a couple of leading battery manufacturers of 12 V batteries.

Roger Pham

The Impala Stop Start has comparable internal dimension to the Camry Hybrid 2014, yet is more expensive.
The Camry Hybrid has suggest retail price of $26,300 vs. the Impala SS is priced at $27,000. The Camry Hybrid is capable of 41 mpg combined, while the Impala SS has 25 mpg combined, or 64% higher MPG, which will translated into much higher overall cost due to high fuel cost.

For example, at $3.5/gallon, the Camry Hybrid's fuel cost will be 8.5 cents/mile while the Impala costs 14 cents/mile, or 5.5 cents/mile higher. At 160,000 miles, the Impala will cost $8,800 MORE due to fuel cost, plus a $1,000 more initial cost will bring the cost differential to almost $10,000 in favor of the full hybrid vs a comparable stop-start hybrid! And that's not counting on service and repair of the transmission and the brake on the Impala vs none on the Camry hybrid which will amount to a few thousands dollars more!

Why does Navigant predict an overwhelmingly larger number of stop-start vehicles over full hybrids by 2035?



The Impala is a much bigger car at 201 inches vs 189 for the Camry. Cargo capacity is almost 50% more at 18.8 ft3 vs. 13.1. The Impala is bigger than the $31,000 Toyota Avalon that gets similar mpg. The Avalon hybrid starts at $35.5K, but then you've spent your "savings" up front, and still have less room in the trunk.

Also, list price is misleading for Chevrolets. Nobody should ever pay list for a GM car. GM is offering $2,000 off list right now, and the dealer will likely match that.

Roger Pham

You should know that the passenger seating sizes are practically comparable between the Impala and Camry. Passenger volume of the Camry is 101 cuFt while the Impala is 105 cuFt, within a few percent. The trunk space reduction is the downfall of all HEV's but can be quickly remedied by the use of smaller fuel tank and eliminating the spare tire, which many car models do not come standard w/ spare tire anymore!

Now, I would like for you to compare the Malibu 2LT 2014 with stop start comes standard at $25,300 with a comparatively equipped Camry Hybrid LE @ $26,300 to see which car will cost less overall after 160,000 miles of driving! The Malibu and the Camry have almost exact internal dimension and space, and are classified within the same class. Hint: the Camry Hybrid will cost ~$8,000-9,000 less after 160,000 miles of driving.



Good luck getting your Toyota dealer to install a smaller fuel tank, re-engineer the chassis, etc, at no cost to you.

The fact is that an Impala can carry 50% more stuff in the trunk, which is a huge deal for a family (these are family cars after all). If you do not need the space, then the Malibu is the car for you, or the Prius. No sense driving around in an empty car.

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