Manufacturers are under tremendous pressure to improve fuel economy while reducing emissions. In 1975, the government established a standard called CAFE (Corporate Average Fuel Economy), which the manufacturer must meet or face stiff fines. In the last couple of years, the government has drastically increased the fuel economy standard and, at the same time, dramatically lowered the acceptable emissions standards.
So, just how much have these standards changed? By 2026, the new standard will require a fleet-wide average of 49 mpg and an increase of “8-10% per year” over the past several years. In addition, the fines for noncompliance have almost tripled. This means that for every truck getting 20 mpg, you need a car getting 70 mpg to offset the difference from the standard. On the emissions side of the standards, each type of pollutant has dropped dramatically over the past several years. For example, CO2 standards have dropped from 118.1 grams per mile to 82 grams per mile in 2026.
This is one of the main reasons many manufacturers are on the EV bandwagon. As an incentive to the manufacturers to produce EVs, the EPA uses a multiplier to calculate the credit the manufacturer will receive in their CAFÉ fleet-wide calculation when they produce an EV. The new Ford Lightning is credited at 237.7 mpg. That type of credit goes a long way to make up for those trucks getting 20 mpg.
The environmental groups are pretty upset with how this works, so they are pushing to eliminate the multiplier for EVs. Now, you might say that is a good idea, but hold on as that Ford Lightning would only receive a credit of 67.1 mpg. This would drive the manufacturers to produce even more EVs as they would need to produce more just to offset the loss in credits from the changes on paper.
As you can see, this is a pretty complicated subject, especially when politicians get involved and have little or no understanding regarding how their legislative changes will impact the vehicles this industry services. In order to keep internal combustion-equipped vehicles afloat, manufacturers have pulled out all the stops and are looking for even the smallest gain in fuel economy or reduction in emissions.
The customer is often unaware of the change and is concerned that their new car does not seem to operate like their old car. Neutral Idle is an excellent example of this. Neutral idle has been implemented in numerous vehicles, from heavy trucks (Allison Transmissions) to your family car. Numerous manufacturers utilize this technology, so you need to be aware of the type of concerns that this technology can generate.
Let’s look at a typical 6T40 (RPO’s MNH, MNK) application equipped with neutral idle. Some neutral idle applications will activate once the engine is warm and you bring the vehicle to a stop with your foot on the brake. Some are a little bit more restrictive, such as requiring the vehicle to be in grade braking mode before coming to a stop. No matter the criteria, the bottom line is with the vehicle stopped and neutral idle active, whichever clutch is used to drive the vehicle forward will be barely released, lowering the load on the engine, which reduces the engine emission output and increases the engine fuel economy. Some transmissions, such as Allison’s, have a separate solenoid designated for neutral idle functions, while others use the solenoids already housed in the valve body to provide that function.
In our 6T40 example, when you bring the vehicle to a stop, and the TCM decides it is time for neutral idle to activate, the TCM changes the amount of current being fed through the #5 pressure control solenoid (Figure 1). The #5 solenoid, Q27E, is a normally high solenoid that controls the pressure to the 1-2-3-4 clutch regulator valve. As the solenoid command changes, the regulator valve reduces the pressure supplied to the 1-2-3-4 clutch, leading the clutch to release slightly. When the brake is released, the solenoid command changes and the clutch is again fully applied.
Now, you may be wondering why they do not fully release the clutch. The simple answer is that the clutch can take too long to reapply. Some customers have questions even when using the software as it is currently written. This leads us to a couple of items you should be aware of:
- When the TCM fully applies the 1-2-3-4 clutch as you release the brake and Neutral idle disengages, you will likely feel a bump as the clutch applies. This is considered “NORMAL”. Now, the customer will say that the car doesn’t always have that bump when I release the brake at a stop, which is true. However, it is also true that neutral idle does not always activate when you come to a stop with your foot on the brake, as you have a host of criteria that must be met before the function is activated.
- Shudder/Surge while stopped with neutral idle activated. We have talked about this in the seminars a couple of times through the years. GM has redesigned the 1-2-3-4 clutch on neutral idle applications to address the issues. Basically, the updated discs have a closer flatness tolerance to eliminate the issue.
Like other features in today’s vehicles, many times we wish those features were not there. But as described above, neither the consumer nor the manufacturers are the ones driving this bus.
Until next time, remember, “It takes about 8,460 bolts to assemble an automobile, and only one NUT to scatter it all over the road”.
