P0172 - Diagnostic code too rich mixture
Machine operation

P0172 - Diagnostic code too rich mixture

29.08.2022 /

Technical description of the OBD2 trouble code - P0172

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 code P0171, a rich mixture error is a system error. That is, it does not indicate a clear breakdown of the sensors, but the parameters of the amount of fuel go beyond the limit value.

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

Error signaling conditions

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

Symptoms of a P0172 trouble code may include:

  • Frequent fires.
  • Excessive fuel consumption
  • The engine light is on.
  • Only these general symptoms may occur in other codes.

Possible causes of the p0172 error

OBD II Diagnostic Trouble Code (DTC) P0172.

in order to understand what caused the rich mixture error, you need to make a list of reasons for yourself using a small algorithm.

The enrichment of the mixture appears due to incomplete combustion (excessive supply or lack of air):

  • when the fuel does not burn out, then the candles or coils do not work 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 rarely can happen, but lack of air is a typical problem. The air supply to the fuel occurs on the relationship between the MAP sensor and the lambda probe. But in addition to sensors, the problem can also be caused by a violation of thermal gaps (engines with HBO), mechanical damage to various gaskets and seals, malfunctions in the timing, or insufficient compression.

in order to deal with all the possible sources that led to the failure, the check is carried out according to the following points:

  1. Analyze information from the scanner;
  2. Simulate the conditions for the occurrence of this failure;
  3. Check components and systems (good contacts, lack of suction, operability), which can lead to error p0172.

Main checkpoints

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

  1. DMRV (air flow meter), its contamination, damage, loss of contact.
  2. Air filter, its clogging or air leaks.
  3. Oxygen sensor, its incorrect functioning (degradation, wiring damage).
  4. The adsorber valve, its incorrect functioning affects the trapping of gasoline vapors.
  5. Fuel rail pressure. Overpressure, may be caused by a faulty pressure regulator, damaged fuel return system.

Troubleshooting P0172 mixture too rich

Therefore, in order to find the guilty node or system, you will need to check the MAF, DTOZH and lambda probe sensors with a multimeter. Then check the spark plugs, wires and coils. Measure fuel pressure with a pressure gauge. Check ignition marks. Also check the air inlet and exhaust manifold connections for air leaks.

After correcting the problem, you will need to reset the fuel trim in order to reset the long-term trim to 0%.

Having followed all the recommendations, you will surely be able to cope with the incorrect operation of the internal combustion engine and the installation of the error code P0172 both on the VAZ and on foreign cars like Toyota or Mercedes, as well as other cars with electronic controls. Although often it is not necessary to complete all the points, in most cases by flushing or replacing the DMRV or the oxygen sensor.

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