p0172 Peugeot | What It Means & How to Fix

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Vehicle engine and/or automatic transmission

Code: P0172 - The fuel and air mixture is too rich (too much fuel) in the first bank of engine cylinders.

The P0172 error code on Peugeot indicates that the engine in the first cylinder bank is running with a rich fuel mixture - meaning that too much fuel is being supplied relative to the air. The engine control unit detects this issue through data from the oxygen sensor (lambda sensor) and adjusts the fuel injection accordingly. However, if the adjustment exceeds acceptable limits, this error is triggered.

Causes of DTC P0172 Peugeot

On Peugeot vehicles such as the 206, 307, 407, 508, Partner, and Expert, this fault is most commonly associated with:

Clogging or malfunction of the lambda sensor before the catalytic converter.
A clogged air filter, restricting airflow.
Issues with the fuel injectors (leaking or supplying too much fuel).
Failure of the mass airflow sensor (MAF).
Increased fuel pressure due to a faulty regulator.
Air intake leaks in the intake manifold, disrupting sensor function.

Symptoms of P0172 Error on Peugeot

Increased fuel consumption.
Unstable engine idle.
Loss of power, sluggish acceleration.
Gasoline smell from the exhaust pipe.
Illumination of the "Check Engine" light on the dashboard.

How to Fix OBD P0172 on Peugeot

To resolve the P0172 error on Peugeot, the first step is to check the lambda sensor. If it is dirty or functioning erratically, it should be replaced. Next, inspect the air filter - if it is clogged, it’s best to replace it, as insufficient airflow can lead to a rich mixture. It is also important to diagnose the fuel injectors, as leaking or incorrect injection can cause excess fuel.

Another common cause is a faulty mass airflow sensor (MAF) - it can be cleaned, but if the issue persists, replacement will be necessary. Additionally, fuel pressure should be measured, as excessive pressure is often related to a faulty regulator. Finally, it’s advisable to check the intake manifold for air leaks, as these can cause incorrect sensor readings and further enrichment of the mixture.

Conclusion

The P0172 error on Peugeot indicates an excessive amount of fuel in the mixture. In most cases, the cause lies in a faulty oxygen sensor, issues with the fuel injectors, or the MAF sensor. Ignoring the error can lead to accelerated catalytic converter contamination and reduced engine efficiency. It is best to conduct diagnostics and fix the issue as soon as possible.

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