VAZ 2114: error 0172 - mixture too rich: causes, symptoms and solutions

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Error p0172 means the mixture is too rich (or system too rich). Thus, a re-enriched fuel mixture is supplied to the combustion cylinders. Like the P0171 code, the rich mixture fault is systemic. That is, it does not indicate an obvious malfunction of the sensors, but the fuel quantity parameters exceed the limit value.

OBD II Diagnostic Trouble Code (DTC) P0172.

Depending on the reason that caused the appearance of such an error code, the behavior of the car can also be different. In some cases, noticeable fuel consumption will appear, and in others, only choking at idle or floating speed either on a hot engine or when it is still cold.

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.

Other reasons

Quite often, the cause of the error in question is not gasoline, but air. The latter, in turn, may be supplied too little. Here you will need to check the functionality of the air filter. It sometimes gets clogged and eventually stops performing its main function.

If there are no complaints about the operation of this element, then the reasons may be the following:

• incorrect injector settings;
• DMRV failure;
• increased pressure in the fuel system;
• fuel getting into the lubricant.

In the first case, the opening and closing of the injectors often occurs at the correct intervals, but each time the dose of gasoline is injected too large. It is almost impossible to check the serviceability of this element at home, so you will have to visit a car repair shop. As a rule, nozzles that have become unusable are replaced with new ones.

A breakdown of the mass air flow sensor results in the on-board computer receiving incorrect data on air consumption, which forces the proportions to be changed in favor of increasing the proportion of fuel.

Possible causes of error p0172

To understand what causes the rich mixture error, you need to make a list of reasons for yourself using a small algorithm:

Enrichment of the mixture occurs due to incomplete combustion (excessive supply or lack of air):

• when the fuel does not burn, it means the spark plugs or coils are not working well;
• when it is supplied in excess, the oxygen sensor or injectors are to blame;
• There is not enough air - the air flow sensor gives incorrect data.

Excess fuel can rarely happen, but lack of air is a typical problem. Air is supplied to the fuel through the connection between the MAP sensor and the lambda probe. But in addition to sensors, the problem can also be caused by a violation of thermal clearances (engines with gas turbochargers), mechanical damage to various gaskets and seals, irregularities in the timing belt or insufficient compression.

To deal with all possible sources that caused the failure, the check is carried out on the following points:

1. Analyze information from the scanner;
2. Simulate the conditions for the occurrence of this malfunction;
3. Check components and systems (presence of good contacts, absence of suction, operability) that may lead to error p0172.

Based on all of the above, we can determine the main reasons:

1. Mass air flow meter (mass air flow meter), its contamination, damage, loss of contact.
2. Air filter, clogged or leaking air.
3. Oxygen sensor, its malfunction (degradation, damaged wiring).
4. The adsorber valve, its improper functioning affects the capture of gasoline vapors.
5. Fuel rail pressure. High pressure may be caused by a faulty pressure regulator or a damaged fuel return system.

Reasons for a rich mixture on the VAZ-2114

The formation of a rich fuel-air mixture occurs in a number of cases:

• incorrectly adjusted fuel system. As a rule, this is the result of intervention in the system to reduce gas mileage or increase power;
• air filter clogged. In this case, the required amount of air does not enter the combustion chamber;

A dirty air filter is the most common cause of a rich mixture. If error P0172 is detected, you should first check the condition of the filter.

• incorrectly configured injectors;

Injector inspection

• high fuel pressure in the rail or malfunction of the pressure regulator;
• air flow meter failure. In this case, the sensor transmits incorrect data to the on-board computer, as a result of which the fuel supply system operates in accordance with these indicators;

New mass air flow sensor

• economizer malfunction.

Eliminating the error: mixture too rich

Therefore, in order to find the culprit component or system, you will need to check the MAF, DTOZh and lambda probe sensors with a multimeter. Then check the spark plugs, voltage wires and coils. Measure the fuel pressure with a pressure gauge. Check the ignition marks. And also check the connections at the air inlet and exhaust manifold for air leaks.

By following all the recommendations, you will probably be able to cope with incorrect engine operation and the setting of error code P0172 both in VAZ and foreign cars like Toyota or Mercedes, as well as other cars with electronic controls. Although it is often not necessary to complete all the points, in most cases it is necessary to flush or replace the mass air flow sensor or oxygen sensor.

The main signs of the error and for which car brands it is typical

With a rich fuel mixture, engine malfunctions can manifest themselves in the form of:

1. Floating speed;
2. Choking at idle (hot and cold);
3. Increased fuel consumption;
4. Loss of dynamic characteristics of the car;
5. The appearance of black or gray exhaust gases;
6. Loud pops in the muffler - fuel burns out in the exhaust system. Often appear when releasing the gas pedal.
7. Velvet soot spark plugs black.

All these signs can appear either individually or simultaneously. Ignoring the problem can lead to failure of parts of the cylinder-piston group, spark plugs, and exhaust system elements.

Error p0172 is typical for most domestic cars, for example VAZ 2114, UAZ Patriot, Kalina, as well as foreign cars - Toyota Camry v40, Opel Astra J, Toyota Corolla 150, Chevrolet Lacetti 1.6, Chevrolet Cruze, Skoda Fabia, Subaru, Mercedes, Mazda and others. But the reasons for its appearance are identical for all car brands, so it’s worth dwelling on them in more detail.

Rich - lean mixture

Next, the closed loop algorithm comes into effect (in English terminology – closed loop). By constantly analyzing the signal from the oxygen sensor, the controller changes the composition of the fuel mixture every time the sensor voltage crosses the threshold corresponding to the stoichiometric mixture (ideal fuel/oxygen ratio). Therefore, when the engine is running, the voltage at the output of the lambda probe has a form close to a sinusoid.

As soon as the voltage rises (the mixture turns from lean to rich), the controller, after waiting some time, begins to gradually reduce the injection time, making the mixture leaner. This continues until the voltage at the oxygen sensor drops, indicating that the mixture has become lean. Further, the injection time increases again - therefore the algorithm.

Since, as the vehicle is used, real operating parameters may seriously deviate from the ideal ones specified by the firmware, a long-term correction parameter for the mixture composition is used. It is set by an algorithm and its work can be explained as follows: if for a long time the short-term correction (set by the lambda probe) deviates significantly from zero, then the average value of the deviation is taken into account when calculating the opening time of the injectors even before applying the short-term correction.

For example, our faulty fuel pressure regulator overestimates the amount of fuel that actually enters the cylinders at the estimated opening time of the injectors. Accordingly, the moment of transition from a lean to a rich mixture via the lambda probe will take place with a negative value of the short-term correction: the mixture will have to be leaner constantly. The self-learning algorithm will remember this negative correction.

Thus, even with serious deviations in data from the sensors and the actual state of the engine, the injection system maintains the specified mixture composition. However, any correction has its limits, and when the correction parameters go beyond the limit values, the Check Engine indicator will light up.

Codes related to P0172

When diagnosing trouble code P0172, you may also encounter other errors:

• P0170 - the fuel-air mixture ratio is impaired, bank 1.
• P0173 - the fuel-air mixture ratio is impaired, bank 2.
• P0175 - mixture too rich, bank 2.
• P0101 - The air flow sensor output signal is out of range.
• P0104 - intermittent signal from the mass air flow sensor.
• P030x - Cylinder misfire is random or specific.
• P0171 - mixture too lean, bank 1.
• P0174 - mixture too lean, bank 2.

Causes and symptoms of error P0172

As soon as the correction parameters (usually displayed as percentages in diagnostic programs) fall below a specified threshold (for example, -70%), an error with OBD-II code P0172 is automatically recorded. To understand the reasons for the occurrence of such an error, you need to know that the composition of the ECU mixture itself is unknown; it is based solely on the voltage at the output of the lambda probe.

Dirty lambda probe

Something else useful for you:

Therefore, the first reason that can cause error P0172 is simple contamination of the lambda probe measuring element with soot. In this case, even with a very lean mixture, oxygen from the exhaust gases does not penetrate through the carbon deposits to the lambda probe, and the output will always have a signal corresponding to a rich mixture. Accordingly, the injection ECU will reduce the fuel correction parameter until it starts to go off scale. For the algorithm, this will cause the P0172 error to be indicated.

Without diagnosis, the symptoms are obvious. A cold engine starts normally or with slight difficulty (since the algorithm is turned off during starting mode and when warming up), then the stability of the engine worsens and the car stalls under load. The candles are covered with white soot or even have signs of overheating (the combustion temperature of lean mixtures is higher). During diagnostics, there is no “sine wave” at the output of the lambda probe, the voltage does not change even in forced idling modes, when the fuel supply is turned off, and a working oxygen sensor would clearly indicate a lean mixture.

However, the mixture may actually be rich. On cars equipped with a mass air flow sensor, one of the most likely causes is a malfunction of the mass air flow sensor. Over time, these sensors begin to overestimate readings. If for VAZ engines the normal air flow at idle is 9-10 kg/h, then if the sensor is faulty it can be 15 or more. The author has seen a Gazelle that literally flooded the engine with gasoline, because at idle its air consumption was supposedly 90 kg/h. Moreover, the primitive algorithm did not even consider this a malfunction.

Standards

On average, the correct ratio of air to fuel is 15 kilograms to 1. When:

• more oxygen is supplied than normal - the mixture is called lean;
• if there is more gasoline - rich.

In some cases, the proportion is violated, but control over it is entirely the prerogative of the ECU; it receives data from different sensors. Problems with a lean mixture are indicated by a noticeable decrease in fuel consumption against the backdrop of a drop in engine power.

If too much gasoline enters the injector, then you will have to refuel more often. At the same time, there are several rather dangerous nuances - they cannot be discounted under any circumstances.

How to resolve the error

Regardless of the cause of error P0172, you should not delay repairs; a rich mixture will shorten the life of the catalyst. The most likely sources of problems are checked and eliminated first:

1. Examine the candles. Check by the presence of black soot that the mixture is over-rich.
2. On vehicles with a return line, remove the hose from the regulator and try to bleed it to ensure it is not pinched anywhere along the way to the gas tank.
3. Find out the correct fuel pressure values ​​for your car. For a VAZ with a drain ramp it is 3 bar, with a drainless one - 4. Please note that the pressure on the drain ramp is measured with the vacuum pipe removed from the regulator, otherwise the readings at idle will be 0.6-0.5 bar lower! The pressure gauge itself for measurement can be inexpensively purchased or borrowed.
4. Connect the tester to the signal wire of the lambda probe in voltage measurement mode. It is more convenient to use pointer instruments - they do not have the same inertia as digital ones; on a working lambda probe, you can see the needle oscillate from 0.25 to 0.75 V.
5. Measure the voltage at the output of the mass air flow sensor with the engine turned off, comparing it with the standard one, if it is possible to find it out. For example, for VAZ sensors it should not be higher than 1.03 V (Bosch) and 0.04 V (Siemens).
6. Check the level and condition of the engine oil.
7. Without “catching” the source of the problem, contact the service - for a qualified diagnostician there will be no problems here.

Video: P0172 Rich mixture

The fuel mixture entering the engine cylinders must have strictly defined proportions of fuel and air content. If their quantity changes in any direction, the result is either a lean mixture, with low fuel content and high air content, or an enriched mixture, in which there is too much fuel.

When too much fuel - gasoline or diesel - is supplied to the combustion chamber with insufficient air, this leads to improper engine operation.

Incomplete combustion occurs because there is not enough oxygen. Therefore, the residues are released through the exhaust valves and further into the exhaust pipe. As a result, several problems arise at once:

• Fuel burns out outside the combustion chamber, which leads to rapid wear of valves and other elements.
• The engine consumes too much fuel, but its power only decreases, and it works intermittently, it may not start or stall.

How to proceed

You will need to check:

• whether the sensors are working correctly;
• whether the settings of the on-board computer have been changed;
• Is the air filter working?

First of all, it is necessary to remember whether the on-board electronic system has been reconfigured. It often happens that the problem appears precisely after the ECU has been reflashed.

Here, the power unit usually works normally for some time, but eventually, if the new settings do not correspond to the current ratings of the installed sensors, the problem makes itself known. Ultimately, fuel is supplied to the injector incorrectly.

In addition, there is a possibility of a malfunction in the injection system after the sensor responsible for air flow or some other built into the fuel circuit has been replaced.

In other cases, when the breakdown is not related to the above reasons, you will need to diagnose the power unit using a computer. To do this you will have to go to a car service center.

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.

This situation requires immediate intervention - diagnosis and adjustment or repair.

Standards of air in the fuel mixture

Fuel mixture composition diagram An average engine requires approximately 15 kg of air and one kilogram of gasoline for normal operation. If this proportion is shifted towards air, then the mixture is considered lean, if on the contrary - rich.

Of course, in different operating modes the proportions of air and fuel may be different and they must be fully controlled by electronics using several sensors. Thus, with a lean mixture, fuel consumption will be slightly lower than the rated value, but the engine characteristics will not correspond to the nominal ones.

With an over-enriched mixture, fuel consumption can increase significantly, and in addition, several other dangerous moments arise.

Possible causes of error p0172

The system that forms the fuel mixture operates based on data from a pair of main sensors:

• The lambda probe, located in the exhaust manifold, measures the amount of unburned oxygen. When the mixture contains one part fuel and 14.7 parts air, the sensor returns a value of 1, that is, the composition is optimal. Otherwise, it returns other values, based on which the composition is adjusted. This works like feedback.
• The MAP sensor measures the absolute pressure in the intake manifold, helping to calculate the air density in this place and its flow.

In addition, information from other sensors is used - camshaft and crankshaft position, air temperature and throttle position. Different conditions are taken into account, including gaps in different temperature conditions - on a cold and hot engine, in summer or winter conditions. All this allows you to adjust the composition of the mixture.

If any of the sensors transmits an incorrect value, this may indicate either a dangerous situation in a particular unit or a problem with the sensor itself. And this can lead to the appearance of error p0172 - mixture too rich. It can actually be formed due to incorrect initial data.

Signs of a rich mixture on a VAZ-2114

A too rich mixture on a VAZ-2114 manifests itself not only by issuing error p072, but also by the following symptoms:

• high gas consumption. Moreover, consumption increases sharply and is explained by inefficient consumption of the fuel mixture;

Soot on the spark plug with a rich mixture

• loss of engine power. A mixture in which the air content is less than normal burns more slowly than usual, and often not completely. As a result, the piston is not provided with optimal force, which is why the engine power decreases;
• black smoke from the exhaust pipe. The reason lies in the lack of filtration of gas from gasoline combustion;

Black smoke with rich mixture

• the appearance of strong pops in the muffler. The reason is a lack of air in the engine cylinders.