Rich mixture: What is Error P0172 Code and What Does it Affect

All about error P0172 code: what it means, what is dangerous, how to fix it

Contrary to popular belief, too high concentration of gasoline in the cylinders is not so harmless.

Rich mixture: what does it mean

Error Code P0172 is deciphered as “rich mixture”. This means that in the cylinder (one or more) the specified ratio of fuel and air is violated. They also say that “the injector is overflowing”.

This error is applicable only to gasoline engines – diesel engines have their own diagnostic codes.

Note that enrichment of the mixture can also be standard. The standard proportion (called stoichiometric) is considered to be 14.7/1. That is, there should be 1 part of gasoline for 14.7 parts of air. However, this ratio can be changed at any time by the electronic control unit (ECU).

For example, modern engines with direct injection in some modes are capable of operating on an ultra-lean mixture. And vice versa: during a cold start, more fuel is injected until the engine begins to warm up.

Modern control systems constantly change the proportion, based on data from dozens of sensors. But when the situation gets out of control, an error is recorded in the ECU memory, and the driver is given a warning in the form of a Check Engine light.

Causes of error P0172 Code (rich mixture)

It is important to understand that “overflow” is not always associated with injectors and excess injected gasoline. Violation of the composition specified by the program may also be associated with a low oxygen concentration. In other words, the fuel supply is normal, but there is not enough air. Below we will consider the main options for the appearance of error P0172.

Lots of fuel

The injectors may indeed be to blame here. If one or more of them are leaking or supplying too much gasoline, the mixture proportions will be disrupted. This may also include a faulty fuel pressure regulator (FPR) or problems in the line draining excess into the tank, the so-called “return line”.

Not enough air

If the amount of fuel is normal, there may not be enough oxygen. Often the cause of P0172 is incorrect operation of the throttle valve, which does not open to a specified angle. In this case, an additional error is often displayed – actually on the throttle sensor.

Also, incorrect readings of the mass air flow sensor (aka DMRV, or MAF sensor), absolute pressure sensor (MAP sensor), and coolant temperature sensor (CTS) can disrupt the correct ratio of air and gasoline.

There may be two of the latter in the system, and if one is quite “harmless” – responsible for the readings of the instrument needle, then the second directly affects the mixture formation depending on the temperature of the antifreeze.

“Electronic” reasons

This may include all sorts of electronic failures, although this is quite rare. However, damaged control unit memory may well cause “glitches”, including a rich mixture error.

Signs of a rich mixture

If the P0172 code is present, in addition to the Check Engine symbol appearing on the panel, the car’s behavior will also change. The overall picture on the move will be similar to that with other mixture formation faults. These are jerks, loss of traction, not always a quick and adequate response to the accelerator pedal.

Also, a rich mixture is often characterized by the presence of black or dark gray exhaust, increased fuel consumption, pops in the muffler and even drops of gasoline flying out of the pipe. In this case, starting, especially on a cold engine, can be difficult.

Why is a rich mixture dangerous?

Unlike the lean mixture problem (P0171), the “mirror” error P0172 does not carry the risk of detonation – one of the most harmful phenomena for the engine. However, do not think that “overflow” is harmless.

The result of a constantly enriched mixture is incomplete combustion of fuel, which not only reduces efficiency and increases consumption, but also forms deposits in the combustion chamber.

If you ignore the problem for several months, the carbon deposits on the cylinder walls, bottom and piston rings will reach the stage where the engine will have to be opened. In addition to the drop in dynamics, increased consumption and smoke, oil burnout and physical wear of the cylinder-piston group will be added.

How to fix error P0172 Code

Obviously, the solution to the problem will directly depend on the source. In one case, it is enough to replace the leaking injector, in another, you will have to deal with the floating readings of the sensor, etc. To accurately understand the cause, you will first need a diagnostic OBD scanner.

As a rule, in addition to the P0172 error itself, several more are recorded in the memory of the electronic “brain” – they are the ones that will directly or indirectly indicate the faulty element.

For example, in addition to stating the presence of a rich mixture, the computer can issue errors for a specific sensor or report problems with the injector.