Trouble Code P0172 – Fuel Mixture Too Rich (Bank 1)

Technical description and interpretation of error P0172

This diagnostic trouble code (DTC) is a generic powertrain code. The P0172 code is considered a common code because it applies to all makes and models of vehicles. Although the specific repair steps may vary slightly depending on the model.

To operate correctly, the engine must add the right amount of fuel to the amount of incoming air. The correct air-fuel ratio is essential for optimal power and fuel efficiency.

The engine control unit (ECU) uses a number of sensors to determine the amount of fuel that needs to be added. Most often, the ratio of air and fuel in the mixture is determined based on the readings of oxygen sensors by calculating the amount of oxygen and carbon monoxide in the exhaust gases.

The most optimal ratio of air and fuel in the mixture supplied to the engine cylinders is 14.7:1. It is this ratio that is necessary to achieve maximum engine power and optimal fuel consumption.

During normal operation, the ECU monitors the balance between rich and lean mixture. Simultaneously monitoring short-term and long-term fuel balance (STFT and LTFT). Typically the fuel adjustment is 3% of the ideal value. This depends on the current air temperature, coolant and load.

Engine problems such as high fuel pressure, a distorted MAF signal, or a faulty fuel injector can increase fuel consumption. Due to these problems, incorrect air flow data is received, which will lead to a saturated condition.

The ECU will try to compensate for the imbalance in the fuel mixture. If the fuel ratio exceeds 25% of the optimal value, the control unit will determine this as a malfunction. Sets diagnostic code P0172 - Fuel Mixture Too Rich (Bank 1).

P0172: mixture too rich error. Diagnostic code p0172 rich mixture

Error p0172 indicates a very rich mixture (or system too rich). It turns out that a too rich mixture of fuel enters the combustion cylinders. Like the P0171 code, the rich mixture error is in the system. Since this does not indicate an obvious malfunction of the sensors, the fuel mixture volume indicators go beyond the maximum value.

OBD II Pattern Diagnostic Trouble Code (DTC) P0172.

Based on the reason that caused the specified error code to appear, the behavior of the car is also different. Sometimes there is a noticeable consumption of the fuel mixture, and sometimes it just chokes at idle, or the speed fluctuates on a warm engine, or, if on a cold one.

How does the error signal appear?

The engine should be running, and the supply of the fuel mixture will occur with the opposite connection to the oxygen sensor (lambda probe), but there is no error from the coolant sensor, the temperature sensor of the absorbed air, the specific pressure (MAP sensor), the air pressure sensor, the air pressure sensor and the damper position measuring device throttle. When the average total of short and long fuel mixture adjustments is less than 33 percent, a little more than three minutes of the seventh test time. The indicator signal lamp on the instrument panel will go out only when a failure is not found after 3 checked diagnostic cycles.

Possible reasons that led to error p0172

In order to figure out why the enriched mixture error appeared, you need to write down all the reasons using a small algorithm:

Enrichment of the mixture occurs when it does not burn completely (too much is supplied or there is not enough air mass); non-combustion of fuel may indicate poor performance of the spark plugs or coils; when the flow is high, the fault lies with the oxygen sensor or injector; there is not enough air - the air flow sensor provides incorrect information.

An excess of the fuel mixture is very rare, but a lack of air mass is a common cause. Air is supplied to the fuel mixture through the interaction of the MAP sensor and the oxygen sensor. However, in addition to the sensors, the cause is also caused by the breakdown of thermal gaps (engines with gas turbochargers), damage to the mechanics of various gaskets and seals, malfunctions in the timing belt or lack of compression.

To analyze all the probable reasons that led to the failure, everything is checked according to the following points:

1. We analyze the information from the scanner.
2. We simulate the conditions for finding such a breakdown.
3. We check the components and mechanisms (presence of good contacts, leaks, functionality) that lead to the appearance of error p0172.

Based on everything listed, we determine the main reasons:

1. MAF (mass air flow meter), its clogged, damaged, loss of contact.
2. Air filter, clogged or air leakage.
3. Oxygen sensor, its incorrect operation (decomposition, damage to wires).
4. The adsorber valve, its incorrect operation affects the capture of gasoline mixture vapors.
5. Pressure in the fuel rail. Increased pressure may appear due to a faulty pressure regulator or a damaged fuel mixture return system.

Eliminating errors of a very rich mixture

It turns out that in order to find the culprit node or system, you need to check the MAF sensor, DTOZH and oxygen sensor using a multimuter. Afterwards, check the spark plugs, wiring and coils. We measure the pressure of the fuel mixture using a pressure gauge. Checking the ignition marks. And we also check the connections at the air mass inlet and at the exhaust manifold to see if there is air leakage on them.

After fixing the problem, you will need to reset the fuel mixture adjustments to reset the long adjustment to zero percent. Having done everything this way, you will most likely cope with the incorrect operation of the engine and the installation of error code P0172 both on the VAZ and on foreign cars such as Toyota, or Merc and other cars with electronic control. But, often it is not necessary to do all the points; in many ways, washing or changing the mass air flow sensor, or the oxygen sensor, solves the problem.

Symptoms of malfunction

The main driver symptom of P0172 is the MIL (Malfunction Indicator Light). It is also called Check engine or simply “check light”.

They can also appear as:

1. The “Check engine” warning light on the control panel will light up (the code will be stored in the ECM memory as a malfunction).
2. Floating speed, the car engine may operate unstably.
3. Increased fuel consumption.
4. The engine stalls or has trouble starting.
5. Black smoke from the exhaust pipe.

The severity of the P0172 code is higher than average, so it is recommended to fix the problem as soon as possible. Most likely, with this problem, you will be able to continue your trip, but fuel consumption will increase. And due to the low O₂ content and poor combustion of the fuel, problems with the catalyst are possible in the future.

How does error P0172 manifest itself?

The air-fuel mixture can be over-rich for several reasons, depending on which the behavior of the car will change. So, with error P0172, the car may behave as follows:

• A cold engine will “choke” until it warms up completely;
• The engine will “choke” in a cold and warm state at idle, and the speed will begin to “float”;
• Fuel consumption will increase;
• The car will become less playful.

Symptoms of the P0172 code may occur together or separately from each other.

Reasons for the error

A P0172 code may mean that one or more of the following problems have occurred:

• The mass air flow (MAF) sensor may be dirty or damaged.
• The air filter is dirty or contains oil.
• Possible vacuum leak.
• Fuel pressure problem.
• Damage to the fuel injector, allowing too much fuel to enter the combustion chamber.
• Worn spark plugs.
• The fuel pump check valve may have failed.
• The PCV valve is leaking or has failed.
• The EGR valve may be stuck.
• There is a leak in front of the oxygen sensor (lambda sensor).
• EVAP valve leaking.

How to Troubleshoot or Reset Trouble Code P0172

Some suggested steps to troubleshoot and fix error code P0172:

1. Inspect all vacuum and PCV hoses, replace if necessary
2. Clean the mass air flow sensor. It's best to remove it and clean it with electronics cleaner or WD. Be careful not to damage the MAF sensor, make sure it's dry before reinstalling.
3. Inspect the fuel lines for cracks, leaks, or pinches.
4. Check the fuel rail pressure.
5. Check the fuel injectors; they may be dirty. Use fuel injector cleaner or have them professionally cleaned/replaced.
6. Make sure there is no exhaust leak before the first oxygen sensor.

What does code p0172 mean?

Error p0172 appears just when the mixture is too rich. This is a system error that can occur either accidentally or during real failures. It may appear by chance when the engine has just started, and incorrect data has been received from the sensors several times in a row. When everything returns to normal, this message disappears.

But if this is a real problem, then the driver himself may feel that the car is not behaving as usual - the engine is “choking”, does not hold speed, pulls weakly, malfunctions, and may even stall.

Diagnosis and problem solving

A dirty MAF sensor can skew air intake measurements and therefore skew fuel injection calculations. Next, check the fuel pressure to make sure it is in the correct range. Excessive pressure, due to a faulty pressure regulator or a compressed line tube, will cause more fuel to be injected than the ECU expected.

Check that the ECT and IAT (inlet air temperature) readings are correct. The ECU can pick up blocked sensors, so it's good to check that the ECT and IAT readings are within the normal range.

For example, if the engine is running for half an hour on a hot day, the ECT should show a temperature of about 80°C. If it still reads 0°C, the ECU will richen the air/fuel mixture to compensate, resulting in a rich condition.

Reduced fuel pressure

With the engine running, record the fuel pressure, and then stop the engine. Fuel pressure may drop slightly but should remain stable for at least 10 or 15 minutes.

If fuel pressure continues to drop, you may have a leaking fuel injector, which will result in a rich and possibly non-ignitable condition.

Valve blocking

A faulty valve in the cylinder head dumps unburned fuel into the exhaust gas stream. Check and correct this problem before attempting to correct a rich air/fuel mixture error.

Pay attention to other trouble codes that may be present at the same time as P0172. For example, for VVT (variable valve timing) or ignition system.

Traffic fumes

Check the exhaust system for leaks, especially in front of the first O₂ sensor. Damage can be mechanical, in the form of cracks, or caused by corrosion.

The entry of atmospheric air before this sensor can distort the oxygen content measurements. At the same time, the ECU will try to compensate the mixture and add fuel.

Error conditions

The engine must be started and the fuel supply occurs with feedback from the oxygen sensor (lambda probe), and there is no error from the coolant sensor, intake air temperature sensor, absolute pressure (MAP - sensor), DPPV, DPKV and throttle position sensor. When the average total values ​​of short-term and long-term fuel trims are less than 33% for just over 3 minutes out of the 7th test period. The indicator light on the instrument panel will go out only if the diagnostics does not detect a failure after three test cycles.

On which cars is this problem most common?

The problem with code P0172 can occur on different machines, but there are always statistics on which brands this error occurs more often. Here is a list of some of them:

• Audi (Audi a4, Audi a6)
• BMW (BMW X5, F10)
• Cadillac (Cadillac SRX)
• Chery (Chery Amulet)
• Chevrolet (Chevrolet Aveo, Cruz, Lacetti, Orlando, Rezzo, Spark, Tahoe, Trailblazer, Epica)
• Chrysler (Chrysler Voyager, Pacifica, Sebring)
• Citroen (Citroen C4, C5)
• Daewoo (Daewoo Matiz, Nexia)
• Dodge (Dodge Dakota, Intrepid, Caravan, Ram, Stratus)
• Fiat (Fiat Albea, Doblo)
• Ford (Ford Mondeo, Focus, Fusion)
• Geely (Geely MK)
• Honda (Honda Accord, Jazz, Odyssey, SRV, Fit, Civic)
• Hover
• Hyundai (Hyundai Getz, Tucson, Elantra)
• Jaguar (Jaguar XJ, X-Type)
• Jeep (Jeep Grand Cherokee)
• Kia (Kia Rio, Sid, Spectra, Sportage, Cerato)
• Land Rover (Land Rover Range Rover)
• Lexus (Lexus gx470, is250, rx300)
• Lifan
• Mazda (Mazda 3, Mazda 6, Mazda cx5, Mazda cx7, Mazda RX-8, Surname, MPV)
• Mercedes (Mercedes m272, ml350, w164, w203, w204, w211, w212, w221)
• Mitsubishi (Mitsubishi Lancer)
• Nissan (Nissan Almera, Vingroad, Primera, Sunny, Skyline, X-Trail)
• Opel (Opel Astra)
• Peugeot (Peugeot 207, 308, 407, 408, 3008)
• Porsche (Porsche Cayenne)
• Rover
• Saab
• Skoda (Skoda Yeti, Octavia, Rapid, Fabia)
• Ssangyong (Sangyong Kyron, Rexton)
• Subaru (Subaru Outback, Impreza, Tribeca, Forester)
• Suzuki
• Toyota (Toyota Avensis, Allion, Auris, Vish, Gaia, Camry, Corolla, Noah, Prius, Probox, Rav4)
• Volkswagen (Volkswagen Golf, Jetta, Caddy, Passat, Polo Sedan, Tiguan)
• Volvo (Volvo s40, s60)
• VAZ 2107, 2108, 2110, 2112, 2114, 2115
• Gazelle Next
• Lada Vesta, Granta, Kalina, Niva, Priora
• Tagaz Tager
• UAZ Bukhanka, Patriot, 409

With fault code P0172, you can sometimes encounter other errors. The most common ones are: P0106, P0131, P0132, P0134, P0138, P0151, P0170, P0171, P0175, P0300, P0363, P0420, P0501, P2178, P2188.