DTC P0171 And The Connection to Carbon Deposits
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DTC P0171 And The Connection to Carbon Deposits (VIDEO)

Carbon deposits could be causing code P0171. This video is sponsored by Rislone.




Have you gotten a vehicle in lately? It’s stumbling, has suspicious long term fuel trim numbers, and on the scan tool, you may have misfire codes or no misfire codes at all. But by the misfire monitor, you notice that it’s capturing random misfires in some of the cylinders. For example, some vehicles, they might even have a code for P0171 for Bank 1, too lean. So what’s going on?

The cause could be carbon deposits on the intake valves, or even in the combustion chamber. Deposits cause the air to tumble into the combustion chamber, and this turbulence causes air fuel mixture to be unevenly distributed. As a result, when ignited, the flame front can be erratic and leave unburned fuel and create spots that are hot inside the combustion chamber, and eventually, this will lead to carbon deposits.


When direct injection engines hit the three year or 30,000 mile mark, some develop drivability problems due to build up on the next of the intake valves and inside the combustion chamber. There are three reasons why direct injection engines are more prone to carbon deposits. The main reason is that fuel and detergents are not hitting the back of the intake valve.

So by injecting fuel direct into the cylinder instead of at the back of the valve, the gasoline and detergents can’t clean the valve and the port. Leaner mixtures and higher combustion pressures can make the problem even worse over time. A direct injection motor produces more energy from a given amount of fuel and air then a port fuel injected engine.


When a hotspot or a suboptimal flame front is created due to turbulent air, unburned fuel in the combustion chamber, well, it increases. When the valve opens during the intake stroke, it might come in contact with some of these byproducts. So what’s the solution? Suppose an engine has an extreme amount of carbon deposits, in that case, while you may have to remove the intake manifold and get at those carbon deposits with either a cleaner or even mechanically remove them from the valves and the ports.

How do you prevent the problem getting so bad that you have to remove the intake manifold and mechanically clean the valves? Simple, proper maintenance that is scheduled, and also augmented with an intake treatment that can clean the injectors and help remove carbon deposits on the valves and also in the combustion chamber.


Keeping the fuel injectors clean keeps the spray pattern as the engineers intended, and the chemicals can help break up the deposits before they start to cause problems. This can help all of the fuel burn and eliminate that code P0171 for a lean Bank 1. I’m Andrew Markel. Thank you very much.

This video is sponsored by Rislone.

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