What are the Most Frequent Breakdowns of Diesel Cars?

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The complexity of diesel engines to meet emissions regulations and fuel with a higher percentage of biodiesel generate more failures and breakdowns.

Although diesel cars are not going through their best moment, there are still many drivers who have one, or they are contemplating acquiring it, well, let’s see what their most frequent faults are and what we can do to prevent them. The first thing we should know and keep in mind is that today’s diesel is far from the old diesel.

The greater complexity of modern diesel engines and fuels with higher percentages of biodiesel generate a series of failures in this type of engine. In the article, we will discuss its causes and how to prevent them as much as possible. To make things clearer, we will separate the main faults into two large groups: those caused by anti-pollution systems and those caused by fuels.

Breakdowns caused by diesel anti-pollution systems

As we all know, overnight, anti-pollution regulations have changed from night to day, and car manufacturers have forced to vary the exhaust systems radically. Where before we had a collector, an intermediate flask, and a silent rear, today we have a series of additional elements such as catalysts, additional injectors, switchboards, wiring, etc., so that logic makes us reach the following conclusion: the more components, the greater the possibility of breakdown.

We will focus on the three most delicate components or with the highest failure rate.

the most frequent breakdowns of diesel cars

Particle filter

Its function is to trap the carcinogenic particles emitted by diesel engines and are relatively effective in this; However, its installation entails a series of collateral damage.

The biggest problem with this component is that the majority of cars circulate the city, which means that complete cycles of system regeneration can not carry out, which implies the obstruction of said filter and that the check engine light comes on”, With the subsequent visit to the workshop. The cost of this piece can vary from 300 dollars to more than 1,500 dollars, depending on the manufacturer and the brand.

EGR valve

It is a valve that recirculates the exhaust gases and reintroduces them into the intake of the engine. The objective is to burn again those fuel particles that have not completely burned the first time, thus reducing polluting emissions. The problem is that the exhaust gases are not clean in a diesel engine. They are gases full of ashes and fats that adhere to the walls of the pipes.

These gases not only cause breakdowns in the valve itself that seizes, but it also clogs ducts in the cylinder head, intake manifold, and other components. If there is a fault in the valve, the repair is somewhat cheaper than in the previous case, since we can find them from 60 dollars to approximately 500 dollars.

AdBlue system management

SCR catalysts to reduce NOx emissions require the installation of an extra tank with the urea additive and a complicated management system that injects this additive into the exhaust stream in the exact proportion for the chemical reaction to take place and the catalyst neutralize these harmful gases.

This system adds seven elements that can fail:

  • A titrator that measures the level of AdBlue in the deposit: 200 euros)
  • A control unit: from 25 to 100 euros
  • An AdBlue deposit: from 300 to 1000 euros depending on the capacity
  • An AdBlue injector in the exhaust: 50 to 250 euros
  • A special catalyst: from 300 to more than 1200 euros
  • Pipes: 20 to 60 euros depending on length and brand
  • Wiring: 60 to 250 euros also depending on length and brand

The three components most susceptible to failure in this system are the additive titrator, the injector, and the catalyst. As a possible solution to these failures, we will say that what works best is to give free rein to our engines and take them out of the city with relative assiduity. Since our particle filter will thank us, the whole system will clean, we will form automatic regenerations by the car and ultimately extend the dreaded visit to the workshop.

the most frequent breakdowns of diesel cars

Breakdowns caused by the quality of diesel

The new diesel carries a higher percentage of biodiesel. The biodiesel lubricates worse than 100% diesel oil distillate and also attacks certain components of gums and joints. The most veteran engines have no problem. The truth is that they were true rocks; however, as the performance began to increase and the diesel engines exploded, their injection systems were tuned so much that they increasingly demanded better fuel qualities to function properly.

This type of fault has the little solution on our part since the fuel quality is what it is; As home remedies, some add 2T engine oil or injection additives, but no remedy is 100% tested to be considered an effective solution.

The main elements that usually fail due to the quality of fuel in diesel cars are:


They work with very high pressures, and their lower lubricating power erodes their internal parts and the holes of the nozzles so that they stop spraying the fuel well and also pour a lot into the return circuit. Its cost varies greatly depending on the manufacturer and the type of injector, ranging from 240 dollars to 800 dollars on some electric piezo type models.

Pump injector

The first 1.9 TDi of the VAG group mounted this system that was effective and robust, but more expensive than the common rail. Hence they were falling into disuse. New fuels greatly accelerate their degradation. The price ranges between 30 and 120 euros per unit; in a 4-cylinder engine, it would cost us about 350-400 euros.

Rotary Injection Pump

Before the common rail proliferated, rotary injection pumps (such as the Bosch VP44) were very efficient and frequent. They also fall like flies due to the worse lubrication capacity of today’s diesel, and the replacement will cost us around 1,500 euros on average.

High-pressure pumps

Another element that also usually fails due to lack of lubrication is high-pressure pumps that raise the two or three bars to those that receive diesel from the tank to 2,000-2,500 bars of the working pressure in the injection ramp. Your change will make us pay between 150 to 500 dollars approximately.



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