For several years now, the Active Fuel Management (AFM) system, commonly referred to as cylinder deactivation, in GMC and Chevy vehicles has been plagued with issues related to excessive oil consumption. While a fix was supposedly implemented, reports of problems persist. Is the AFM system inherently flawed, or is it just a case of poor execution?
A recent image highlights the ongoing issue, showing how the AFM system continues to consume oil, leaving many wondering if there will ever be a definitive solution. Most GMC and Chevy owners are aware of or will soon encounter this excessive oil consumption issue. What's frustrating is that it appears to occur sporadically—some owners experience it while others don't. GM did release an updated fix as recently as April 2013 (TSB 10-06-01-008G), but the problem remains.
According to owner feedback, it seems that when the AFM system deactivates a cylinder, oil can escape. Some speculate that the pistons in the deactivated cylinders overheat and burn the oil onto the pistons and rings. Officially, GM attributes the issue to oil pulled through the PCV system or oil spray discharged from the AFM pressure relief valve within the crankcase. They state that under normal driving conditions, this discharge isn't problematic. However, under specific circumstances—like extended periods of high engine speeds—the oil spray can increase, leading to excessive deposits in the piston ring grooves, resulting in higher oil consumption and potentially damaged or fouled spark plugs (#1 and/or #7).
Interestingly, GM claims that engine oil consumption becomes noticeable in vehicles with higher mileage (around 48,000 to 64,000 kilometers or 30,000 to 40,000 miles). To put that into perspective, GM considers this mileage to be high! Additionally, in the past, GM required owners to return their vehicles multiple times to demonstrate the problem. Fortunately, this requirement has since been dropped.
GM has also adjusted its acceptable oil consumption levels, increasing it from 1 quart per 2,000 miles to 1 quart per 2,000 to 3,000 miles. This means that if you get your oil changed every 5,000 miles, you could be more than a quart low and still fall within the acceptable range.
In addressing the issue, most owners report that their dealerships replace components such as valve covers, oil deflectors, new lifters, pistons, and rings. They also apply an AFM "shield" designed to prevent oil from escaping. In some cases, entire engines are replaced. Surprisingly, even after these replacements, some owners are experiencing the same problem again, requiring a second or third engine swap.
Many believe the best long-term solution is to disable the AFM system entirely. However, GM dealerships typically refuse to perform this modification. There are aftermarket tuners available for GM vehicles that can disable the AFM system, but doing so sacrifices one of GM's key selling points: improved fuel efficiency.
The concept behind AFM—a system that uses fewer cylinders when full power isn't needed—is theoretically excellent for reducing fuel costs. It also helps automakers like GM meet fuel economy standards and comply with regulations like the 2016 CAFE requirements. But if constant oil top-ups are necessary, does that negate any potential fuel savings?
It’s worth noting that Honda owners have reported similar complaints about their Variable Cylinder Management (VCM) system, which is essentially cylinder deactivation. Interestingly, as of this writing, no Toyota models feature cylinder deactivation.
So, what are your thoughts on cylinder deactivation? Do you think GM's approach to acceptable oil consumption levels is reasonable, or does it overlook significant engineering flaws?
While we ponder these questions, here are some related posts for further reading:
- [Toyota Still #1](#)
- [Toyota Recalls Nearly 1.7 Million Vehicles Worldwide](#)
- [GM Issues Ignition Switch Recall – NHTSA Investigates](#)
- [Consumer Reports Place Two Toyota Vehicles in Top Ten of 2010](#)
- [February 2014 Toyota Sales Slight Decrease – Similar to GM, Ford, Chrysler, and Others](#)
These stories provide additional context and insights into the automotive industry and its evolving challenges.
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