AFM – Active Fuel Management – is a fuel economy-improving solution from GM. It’s designed to activate when your engine is under a light load, such as driving at a slow, constant speed.
In principle, it’s a great idea. Most people rarely need to use 100% of their engine’s horsepower, especially in big V8 motors.
AFM allows the car to “turn off” half the valves to their respective cylinders while the engine’s running. With fewer firing, you can get better mpg – up to 7% more.
The AFM lifters – essential to the process – can fail. It’s not rare; this problem is widespread throughout GM cars.
Here are the signs to be cautious about.
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How Does AFM Work?
Active Fuel Management works using a unique set of valve lifters. These replace half of the standard set usually found in the engines.
AFM lifters are used on half the cylinders in certain V6s and V8s. The other cylinders are fitted with normal lifters.
When the motor is not under a heavy load, the ECU transmits a message to the Valve Lifter Oil Manifold (VLOM) assembly.
Solenoids open, allowing motor oil to flow through the AFM lifters.
Within the lifter, the oil pressure forces latching pins to close. This detaches the inner body from the outer body.
As a consequence, the lifter’s external body moves while the inner body stays stationary. This means it can’t activate the push rod, and the valve remains closed.
With closed valves, the cylinder has no air/fuel intake. Without this, there’s no power.
The piston remains connected to the crankshaft by its con-rod and always stays in motion. AFM doesn’t disconnect the pistons themselves, just the valves.
As you accelerate hard or drive up a hill, the ECU tells the solenoids to close. The system thus turns off, and the engine fires on all six or eight cylinders.
Why Do AFM Lifters Fail?
The leading causes of AFM lifter failure are oil issues, a mistimed switching event (related to the oil), and general wear and tear.
Many owners complain about long-term effectiveness. There is certainly a well-above-average failure rate for this system.
For many owners experiencing issues, the problems start around 70,000 to 80,000 miles.
In particular, watch out for the 2014 to 2019 AFM applications. These are widely reported to be the worst years, and customers are suing.
What Happens When AFM Lifters Fail?
When AFM lifters collapse, the cylinder in question will have low compression during a test.
Often, the lifters fail at the latching pins. The inner and outer bodies either come loose or collapse, making them inefficient as valve operators.
When the valves malfunction, they might not open. This creates a very obvious misfire in that cylinder.
The VLOM (manifold) also commonly develops internal leaks. OBD II readers might show low hot oil pressure (at idle) in the VLOM. If this is the case, check the VLOM filter screen first.
Most AFM problems are related to oil pressure and quality. Low oil levels cause the system to stop working properly.
- Low (or even high) oil pressure can mean the latching pins don’t engage properly, causing them or the inner/outer body to break.
- Dirty oil (sludge) can clog up the solenoid and pins, holding the lifters in one state.
Signs Of AFM Lifter Failure
The symptoms of AFM lifter failure are similar to general engine misfires. That’s because, well, that’s what’s happening.
A misfire creates the following (and more):
- Low power under acceleration
- Rough idle
- Unbalanced engine
- Fouled spark plugs
- Check Engine light
You’ll see your oil consumption increase like an elephant’s drinking it, along with misfires.
When the AFM system is active, the engine sprays oil onto the three or four temporarily unused cylinders. Eventually, this oil – combined with the hot metal – will build up and eventually get past the piston rings into the combustion chamber.
GM introduced a partial fix (a shield to prevent the pistons from sludging up). While the volume of complaints has reduced, it’s still significant.
Check your oil levels and the last oil and filter change date. Do you need a top-up/service?
You might also hear a consistent ticking noise from the valves.
Plugging your car into an OBD II code reader might tell you that the AFM lifter is the problem.
How To Prevent AFM Lifter Failure
The best way to avoid a problem with AFM lifters is to avoid buying a car with an affected engine. AFM only applies to specific V6 and V8 models.
Take extra precautions if you’re wondering whether to get a Cadillac, a Chevrolet truck, or a GMC. The worst offenders appear to be the 6.2-liter L86 and 5.3-liter L83, both of which can be found in the Chevy Silverado and GMC Sierra (among others).
If, however, you already have a vehicle with one of these engines, that’s not possible.
Instead, you’ll have to keep a close eye on your oil. Be even more vigilant than usual in checking the levels and getting an oil and filter change.
Overall, aside from good maintenance, there isn’t much else you can do.
Many recommend an aftermarket chip that overrides the AFM. These chips prevent the solenoids from opening; thus, the lifters perform like standard parts.
Although this will stop any AFM lifter problems, your fuel economy will decrease. You’ll save much more, though, in comparison to the cost of replacing AFM lifters.
Also, bear in mind the risk of an improperly configured chip. These could do irreparable damage to your ECU.
AFM Lifters Have Failed: What Do I Do?
If your AFM lifters are failing, there’s no swift solution. Leaving it will eventually ruin the engine. Unfortunately, your immediate choices are to either take the replacement expense on the chin or scrap the car.
In August 2021, GM was sued in Michigan over the AFM lifter situation. It’s alleged that the company knew that the lifters would fail and replaced the faulty parts with equally defective ones.
The response was for them to issue a notice to authorized dealers. Customers who have experienced lifter problems in affected engines can get either:
- A replacement lifter bank
- A new engine.
Whichever you’re given, it should come along with a five-year warranty.
While this is a significant step and well worth checking out if you’re in this situation, it doesn’t solve the problem. Many people are still out there, waiting for their AFM motor to just stop working.
The legal cases are still happening, with lawyers requesting a large recall.
How Much Does It Cost To Replace AFM Lifters?
In many cases, it’s recommended to replace everything. That is,
- All AFM lifters
- All lifter guides
- Anything else that’s damaged (potentially including the camshaft(s))
Although the parts themselves aren’t too expensive, it’s a labor-intensive job. The engine head has to be removed, inspected, and disassembled.
As such, you can expect to pay up to $2,500. In most cases, you might get it done for somewhere between $1,000 to $2,000.
Yeah. It’s costly if it doesn’t work out.
The AFM lifter situation is widespread. If your car or truck is affected, you’re far from the only one.
Your best option is to pile the pressure on GM to replace your lifters or engine (if necessary) for free.
If you can’t get anywhere, you could either scrap the vehicle or keep it off the road until the lawsuit result comes in. Provided the prosecution is successful, it might signal the start of the end of the notorious AFM lifter problems.