P0299: Low Boost Pressure - Meaning, Causes, Symptoms & How to Fix

Interviewer? What does a P0299 code mean?

CowboyBenWade: This code means you have low boost pressure in your intake manifold. Only cars and truck with a turbo charger or super charger will throw a P0299 code. It means your turbo is not functioning properly. 

Many newer vehicles use for smaller displacement 'forced' induction engines in the hopes of achieving better fuel economy. Whether that works or not is a question for another post. But the premise is that to get a fixed amount of horsepower, you need a fixed amount of air and fuel. Forced induction engines have a pump that's driven either by a pulley on the crankshaft or by an impeller on the exhaust manifold that compresses in the air coming into the engine. With more air, you can inject more fuel, get a more powerful explosion in the cylinder, which produces more power. You can achieve the same fuel/air density of a larger engine and produce the same horsepower of the larger engine.

Forced induction engines are used in Ford's Ecoboost engines and many other manufacturers such as Toyota with the Tundra are following suit. This means there are lots of vehicle on the road with this new part that can fail - and fail they do.

Turbo chargers are the more popular choice than superchargers for a variety of reasons, and they are powered by the flow of exhaust gas. Turbochargers spin at super high RPMs, and that requires constant lubrication. They can spin over 200k RPMs. For comparison, you engines spins between 1500-8000 RPM.  Most engines pump oil from the crankcase into the turbo housing to lubricate it and keep it cool. If this lubrication process ever halts even for a little bit, the turbo can fail completely or become damaged. It can't function for long at those high RPMs without adequate lubrication and cooling.

Sometimes turbos just wear out, sometimes the owner of the vehicle doesn't change the oil frequently enough, and sometimes the vehicle is under heavier load, which makes the turbos heat up and wear faster. For example, modern Ecoboost engines are designed to "spool up" the turbos when needed. Under most driving conditions, the waste gates are open, not a lot of boost pressure is being generated, and the turbo isn't working that hard. This is to save fuel. Just driving down the road at 55mph, you don't need a lot of extra power, so the turbos adjust how much boost they are generating at any given time. All this is controlled by computers, and this is the benefit of turbos - they can dynamically increase power. A naturally aspirated engine cannot do this.

If you're vehicle is under a lot of load - maybe you're towing 8k pounds with your F150 for a ten hour trip, and you might be driving up mountains. Under these conditions, the turbos will be getting really hot because they are working at their max capacity. Compressing air generates heat, the exhaust is hot, and the turbo housing can sometimes get red hot. This is bad for lubrication and bad for turbo life. If you use your truck like this often, the turbos are going to wear out faster. All that heat means the metal is constantly expanding and contracting, carbon is building up in the blades of the exhaust impeller, and oil is getting dirtier. 

Modern gasoline turbo engines like the Ecoboost F150 are designed to last 150-200 miles, but turbos can easily fail anywhere after 100k miles even with proper maintenance. If they lose lubrication, they can fail at any time. This does NOT mean that Ecoboost technology is faulty - it just just means that turbos are high-wear parts, and you should expect to replace them if you keep the vehicle long enough. Due to their inherent design, turbos are just prone to the problems listed above, and there nothing that can be done about it. In the past, this technology was only used on race cars.

As more and more manufacturers move to forced induction, it's gotten more reliable, but they do fail. But with mass production, the parts are cheaper to replace than they have been in the past.

Most diesel engines are equipped with turbos, and those engines last hundreds of thousands of miles without turbo failure/P0299 codes. Semi trucks, Ford Super Duty, Rams, and many others all use turbo-diesels. Many have argued that since turbos last so long on diesel engines, gas engines should be just as reliable and the turbos should last just as long. But due to the following, this is not true.

Diesel engines spin at much lower RPMs than gasoline engines. They have a longer stroke, produce more torque, and they have a more powerful combustion. The pressures are much higher in the cylinders of a diesel engine - that enables it to run at a lower rpm and produce more torque. Therefore, the diesel exhaust gases are several hundred degrees celsius cooler than gasoline engine exhaust. That means diesel turbos stay cooler, and that's the main reason they last longer. They are under less stress. 

If a turbo becomes damaged, it will spin slower that it was designed to spin, causing low manifold pressure. Your engine will have less power, you're dashboard will light up like a Christmas tree from engine codes.

A turbo that's not generating enough boost pressure will need to be replaced. If it's a V6, only one of them may be damaged. Four cylinder engines only have one turbo. It's not a super expensive thing to have done, but you need to make sure you fix the cause of it. If the bearings in the turbo are not getting enough oil for some reason, the repair shop needs to fix that or your new turbo will develop the same problem.

If you get a P0299 code and don't do anything about it, the turbo will eventually self destruct. The bearings will fail, the impeller will come loose, crash around inside the turbo housing, and eventual shower a bunch of metal fragments into your engine. This will destroy all sorts of things. Most engines get fixed before they get to this point. 

Change your oil regularly. Ecoboost engines and all other turbo engines need oil changes more often than their naturally aspirated counterparts. This is due to cylinder blow-by. Cylinders go up and down in the cylinder, and there are rings around the piston to seal the pressure in the cylinder and keep it from 'blowing by' between the walls of the cylinder and the piston. Those gases are dirty with carbon, soot, and the general byproducts of combustion. All engines experience a little bit of leakage around the cylinders, but due to the increase pressure in the cylinders of turbo engines, they will experience more blow by. Those dirty gases go straight into the crankcase, and they make the oil dirtier faster. Dirty oil doesn't lubricate as well.

One of the best ways to avoid turbo failure and increase engine life in general is to change your oil often. Do not let it go more than 5k miles in a turbo engine - disregard whatever the manufacturer says about oil changes. Some recommend 10k oil changes, but expect to be replacing your turbo much sooner if you follow that recommendation in a forced induction engine.

Turbos are expensive compared to some other parts, but the real cost is labor. Turbos are often hard to get to and require removing lots of other stuff. They are usually stuck on the sides of the engine near the exhaust manifold. In a crowded engine bay, they can be complicated to access. Expect to pay around $1000-1500 for new turbos on an F150 Ecoboost. Other engines may be slightly more or less. Since there are so many of these engines on the road now, the parts are cheaper and repairs are more routine.

As stated earlier, turbos have bearings that need lubrication - and sometimes they can leak oil into the intake if there is a problem. Oily smoke will not be burned off in the combustion cycle, and it will flow out the exhaust. Catalytic converters are designed to convert that oil and smoke into C02 and H20. Too much oily smoke will make the catalytic converter work really hard, and it will eventually clog it up. That is an expensive repair because catalytic converters contain precious metals such as platinum, palladium and rhodium. These metals act as catalysts to convert hydrocarbon byproducts into less harmful compounds. Catalytic converters are designed to handle a certain amount of harmful compounds in exhaust gas, but with a leaking turbo, too much of those things will go into your exhaust. This will lead to dreaded and expensive P0420.

Just another reason to change your oil frequently!