Seeing the check engine light on the dash is never a good sign. It can mean that something minor is wrong with your car, but it can also mean that something catastrophic had just happened. A code that’s often found stored in the ECU is the P0172 code. As far as check engine light codes go, this one is somewhere in the middle when it comes to severity.
This specific code is related to the fuel system and shouldn’t be ignored. In this article, we’ll cover everything you need to know about the P0172 code, the causes, symptoms, and how to fix it.
What is the P0172 Code, and What Does It Mean?
The P0172 code stands for “Fuel System Too Rich (Bank 1)”. What this means in plain language is that there’s too much fuel being delivered to combustion chambers on bank 1, or not enough air.
A car engine requires a 14.7:1 air to fuel ratio to work optimally. There are sensors that monitor the amount of air coming in, and the ECU controls when and how much fuel is sent to each of the combustion chambers. The ECU can adjust small differences in the air to fuel ratio. However, if the difference is too big to adjust, the P0172 code is triggered.
There are a couple of things that can cause this, and a couple of specific symptoms to look for.
What Causes a P0172 Fault Code?
Some of the known causes for triggering the P0172 code include faulty fuel injectors, faulty spark plugs, a dirty mass air flow sensor among others. Let’s break these down and see how each affects this condition.
Faulty Fuel Injectors
Faulty fuel injectors are a much more common cause for the P0172 code than people think. Fuel injectors become dirty over time even if every internal part of the engine works perfectly fine.
The fuel burns nearly as soon as the injector sends it to the combustion chamber. A portion of the combustion residuals sticks to the injectors, which is an issue common with Audi fuel injectors on FSI engines. Over time, the fuel injectors get too dirty and the amount of fuel required in the combustion chamber isn’t enough.
On the other hand, fuel injectors can also get damaged from the excess heat which can lead to too much fuel being sent to the combustion chamber.
Faulty Spark Plugs
Faulty spark plugs are also a common cause of this code. Their function is to cause a reaction between the fuel and air, and if there’s no spark, excess fuel will be discovered by the ECU. It doesn’t take long for this issue to come up when there’s a faulty spark plug. Also, they’re often overlooked during regular maintenance checks. On top of that, there are different types of spark plugs available for most engines. In case of the BMW N54/N55 engines, you can get BMW spark plugs with different heat ranges. All of that can affect the combustion process.
Dirty Mass Air Flow Sensor
Only a clean sensor will work properly and send the right information to the ECU. Once they get dirty, they can send false information to the ECU and cause a number of issues that will trigger the check engine light.
A dirty mass air flow sensor is a common cause for the P0172 code because it can send false information about the amount of air coming into the engine. A dirty mass air flow sensor will detect less air than is actually entering the intake, which leads to a rich condition. Fortunately, if your MAF is only dirty, you can easily clean it. However, in many cases the MAF is beyond saving and requires replacement.
Faulty Air-Fuel Sensor or Oxygen Sensor
Because the amount of fuel sent to the engine is determined by a couple of sensors, it’s important that they’re all working properly. The sensor that has the most say in how much fuel needs to be sent to the engine is the air-fuel sensor. If this sensor is faulty (or the oxygen sensor in some cars), it’s likely that the check engine light will be triggered by the P0172 code or a similar one.
Faulty Fuel Pressure Regulator
Sending the exact amount of fuel to the engine wouldn’t be possible without a fuel pressure regulator. Although this part doesn’t break so often, it’s a common cause for the P0172 code.
The amount of fuel differs when you’re cruising at 30MPH and overtaking someone at 80MPH. When more fuel is needed, the electric fuel pump will send more pressure, so if the fuel pressure regulator doesn’t work properly, more fuel can be sent to the engine without there being an increase in actual demand.
Can a Bad Catalytic Converter Cause a P0172 Code?
No. A bad catalytic converter doesn’t cause the P0172 code. It’s the other way around – if the P0172 code isn’t addressed and the issue fixed in a timely manner, the catalytic converter can get damaged to the point that it needs replacing.
It’s a costly repair, which is why it’s recommended to address any fault code stored in the ECU, especially the codes that can cause the catalytic converter to fail.
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What Are the Common Symptoms of P0172 Fault Code?
Some of the most common symptoms of the P0172 code include a rough idle, lack of power, black smoke and a noticeable smell of fuel coming from the exhaust. Of course, the check engine light is the first thing you’ll see.
Not all cars show the same symptoms; it depends on the make, model, and severity of the issue.
Illuminated Check Engine Light
The first thing you’ll notice when the P0172 code is triggered is the check engine light. In fact, any fault code stored in the ECU will trigger this, so having an OBD II scanner at hand will be very helpful. This way, you’ll be able to read the trouble code right away, and you’ll know whether your car is safe to drive or you need to call a towing service.
Rough Idle
This is likely something you’ll notice first. By having more fuel than it needs, the engine will start idling roughly, trying to adjust the air to fuel ratio. Once the difference is too big for the ECU to adjust, the P0172 code will get stored and the check engine light will come up.
Lack of Power
After noticing a rough idle, you’ll likely notice your car isn’t accelerating as fast as it did before. This is a clear sign that there’s likely something wrong with the fuel system. Even though the P0172 code means there’s more fuel being sent to the engine, the fuel can’t be burnt and the car will lose performance capabilities.
Black Smoke Coming From The Exhaust
Black smoke from the exhaust is a standard sign that the engine is running too rich. This is considered a universal symptom of rich running engines and will show on any gasoline-powered car. The only difference is how much smoke you’ll see.
Smell of Fuel
The smell of fuel is an expected symptom being that not all fuel is burnt while the engine is running. It has a distinctive smell, and you’ll sense it only when the car is running.
How to Diagnose and Fix P0172 Code
Now that you know what are the most common causes of the P0172 code, you’ll know how to diagnose the issue as well. It will likely require a few steps, and the first one is to check the ECU codes. Using an OBD II scanner, you’ll get a clear reading of the stored codes. If your car was running the way it should before, you’ll likely find only the P0172 error. If there are no other codes showing up, you can proceed with diagnosing the issue.
The mass air flow sensor should be the first thing you check if you maintain your car regularly and replace the air filter on time. Remove the MAF sensor from your car and clean it with a mass air flow sensor cleaner. It’s a straightforward procedure and shouldn’t take more than 15 minutes to complete. After thoroughly cleaning the MAF sensor, let it dry completely before reinstalling it to the car. Before starting the car, erase the code from the ECU with your OBD II scanner and see if it appears once you start the car.
If cleaning the MAF sensor doesn’t resolve the issue, continue the process by checking the spark plugs. If you’re not sure when was the last time they were replaced, get a set of new spark plugs and replace them. Again, delete the error code with your OBD II scanner before turning your car on and watch if the check engine light comes up on the dash.
If this doesn’t work either, you’ll need to inspect the air-fuel sensor or O2 sensor. This is done by using a multimeter and checking the resistance of each of the sensors. The same applies to the fuel pressure regulator. If there’s a false reading, you’ll need to replace the faulty sensor to fix the issue.
If none of the above things fix the P0172 code, you’ll need to do a thorough inspection of the fuel injectors. There are a couple of ways you can do this, but ultimately, you’ll need to compare fuel injectors and see if any of them are leaking or are stuck open. To fix the issue, you’ll need to replace the faulty fuel injector with a new one.
Does P0172 Clear Itself?
The answer to this question depends on the make and model of your car. Some vehicles clear fault codes as soon as they’re fixed, while other vehicles require manual deletion of fault codes with an OBD II scanner. It’s recommended to clear the codes with an OBD II scanner after attempting to fix the issue, just to make sure the code doesn’t come back.
Can You Drive with P0172 Code?
Although the engine won’t work optimally, most cars are drivable with the P0172 code. When it comes to whether you should drive with this code or not, it’s recommended to avoid driving until the issue is fixed.
Unfortunately, this issue can cause damage to other internal components of the engine and the catalytic converter, which can end up being much more expensive than just cleaning the MAF sensor, for example.
Buy Quality Replacement Parts to Fix P0172
As far as replacement parts go, it’s always the best solution to go with genuine, or OEM parts. Critical components such as any that cause a P0172 code should be replaced by high-quality parts only.
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