Before we realize that there is a problem with the engine, the ECU notices it and turns on the engine fault lamp. As a result of the scan, if the DF121 fault code has been received, it means that an extra sound or vibration has been detected in the engine (or the knock sensor may be out of order), in addition to the explosion sound in the cylinders.
It is understood that the sound of the engine working healthy and the vibration it emits are normal. When there is a problem in the engine, we can understand it from the differentiation of its sound, the jerky operation of the engine, sounds such as clicking, snapping, the differentiation of the color of the smoke.
In a solid vehicle engine, explosions in the combustion chamber are regular, like the beating of a heart. Just as the ECG graph of a healthy heart is a graph with regular ups and downs, if the ECG of the vehicle engine were to be taken, graphs with regular rhythms, such as a heart ECG, would be obtained.
If there is a fault code DF121, it means that there is a deviation in these graphs. In other words, in addition to the normal explosion in the cylinder, there is an aftershock explosion or there is another sound in the cylinder apart from the explosion sound.
The sensor that measures the vibrations and sounds of the engine in vehicles is a knock sensor. If the vibrations detected by the knock sensor are not in the specified standards, the ECU generates the fault code DF121.
Possible problems with the vehicle with the Renault fault code DF121:
- There may not be any symptoms in the vehicle, except that the engine malfunction lamp is lit.
- There may be a knocking sound in the vehicle. The knocking sound is the clicking sound coming from the engine, which experienced ears can distinguish.
- There may be excessive shaking in the vehicle when it goes above a certain speed.
There may be differentiation in exhaust fumes.
What is the DF121 Renault fault code?
The part that is shaped and called the accelerometer is the knock sensor. According to this brief description, the fault code DF121 means that the knock sensor circuit may have malfunctioned.
In practice, the problem may be a little different from this, sometimes the knock sensor circuit or the sensor itself may change, but the problem may persist.
The so-called ”knock” sound is the case when there is another sound-vibration, except for the main explosion in the cylinder. The factor that causes the knocking sound is most often that an aftershock flare occurs after the main explosion due to excessive temperature and pressure inside the cylinder.
This suggests that there may be a timing error. Since there are no spark plugs in diesel vehicles, ignition occurs by spraying the fuel injector with fuel. If the fuel injector is working with problems, there may be a knock problem.
For example, the spraying process may become irregular due to reasons such as clogging inside the injector and the injector breaking, being damaged, which may be the cause of knocking.
Another possibility is that the combustion process in the cylinder is out of order due to vacuum leakage.
The knocking sound can also be caused by a tiny piece of metal inside the cylinder. For example, a tiny metal particle that breaks off from the injector or rings may be vibrating extra.
DF121 Renault fault code solution
First of all, it is checked whether the knock sensor, the electrical circuit supplying the sensor is intact, whether the plug is loose, whether there is damage to its cables.
What kind of complaints are experienced in the vehicle, whether there is a fault lamp lit on the instrument panel, will guide the subsequent fault investigation.
For example, if the battery lamp is on, it may be thought that the knock sensor is not working due to a battery-related problem.
Or, if the electronic malfunction lamp is on, the knock vibrations are judged to be an indirect reflection of the transmission malfunction.
Shaking, shaking, black smoke coming out of the exhaust in the vehicle suggests that there may be a malfunction in the injector or other part related to the fuel system.
If blue smoke is emitted from the exhaust, it is emphasized that the knocking sound may have occurred as a result of the wear of the piston rings or valves.
The simplest solution to the Renault fault code DF121 is the possibility that the knock sensor has failed. The sensor changes and the problem is solved.
The most expensive solution is that the engine needs rectification due to the wear of parts such as piston rings, pistons and valves.