Hello all,

I am new to this forum and would like to describe my car problem, which is unusual because I don't get any error messages or lights on the on-board computer. I hope that someone has had a similar problem and that we can find out what is causing this behaviour.

I have a Škoda Kodiaq TDI DSG engine with 110 kW and four-wheel drive, built in 2017 with 200,000 km on the clock. Maintenance was carried out up to 180,000 km at the official service centre due to the extended warranty. After that, I did all the servicing myself.

I am trying to eliminate the random loss of power (jerking) of the car engine.

This occurs randomly, independently of external temperatures and how the car is driven. During these events, there is a strong decrease in engine power/revs for a few seconds. If I do not accelerate, the engine starts to respond normally after a few seconds; otherwise, if I accelerate, there is a strong fluctuation in revs, which can also last a few seconds. After this transient phenomenon, the engine usually responds normally again, but sometimes I need to restart the car. After that, the car drives normally.

The time between these events varies. For example, four weeks passed between the last two events, followed by several days in a row. When the jerking occurs, no engine fault light comes on and the event is not recorded in the event log.

So far, I have carried out the following replacement and preventive checks to find the cause:

 - change engine oil and all filters (oil, air and fuel).

 - repair of DSG mechatronics and change of oil and filter in DSG gearbox

 - replaced the flywheel.

- cleaned the DPF filter with liquid and manually activated DPF filter regeneration.

 - Cleaned the EGR valve and flaps.

 - tested vacuum hoses and joints

 - Inspected the fuel supply hose.

- Inspected the fuel tank.

 - Tested the operation of pumping fuel from one tank to another (because it is a 4x4 version).

 - Tested the battery.

 - tested the pressure actuator on the turbine.

I assume the issue lies somewhere in the fuel system. So, my question is: are there any components in the fuel system that are not covered by sensors and therefore not measured?

Any hints or comments on how I should proceed with the investigation would be much appreciated.

Thank you

WBR Primoz

Today, I checked the J538 module, which powers the fuel pump. I didn't realise that the fuel pump was three-phase.

I measured the voltage and current in all three phases, which were the same, so I assumed they were OK. When I pressed the accelerator, the voltage on the line coming directly from the engine control unit increased. The voltage at idle was 4.5 V and the voltage on the pump side was 2.2 V.

Tomorrow I will get a new cable and VCDS. My plan is to check the fuel pressure while driving.

WBR P

I'd be grateful for any ideas as to what could be the reason for that behaviour of my car.

Thank you

WBR Primoz

I was able to check all the systems, including the injectors, the high-pressure pump and the pump in the reservoir, and all the values were within the normal range. I am now focusing on the speed sensor. I found on other forums that this sensor can send improper signals that lie about the values, which are sometimes related. The period is also shortening; this effect persists if I drive for 15 minutes. Today I will check the signal with an oscilloscope.

Has anyone had problems with the speed sensor?

On 28/01/2026 at 05:54, primozb2005 said:

I was able to check all the systems, including the injectors, the high-pressure pump and the pump in the reservoir, and all the values were within the normal range. I am now focusing on the speed sensor. I found on other forums that this sensor can send improper signals that lie about the values, which are sometimes related. The period is also shortening; this effect persists if I drive for 15 minutes. Today I will check the signal with an oscilloscope.

Has anyone had problems with the speed sensor?

Hi,

I've recently experienced a similar issue with my 2.0 diesel, and both I and my local mechanic suspect it could be linked to wheel speed sensors.

Oddly, on a recent drive, I had multiple dashboard lights 'on' for a minute or two, notifying me of failures in around 5 or 6 systems from hill-start assist, auto-brake etc etc. Switched off, then on, and they've disappeared.

I plan to get the car scanned next week to see if any faults have been recorded, then I may change the sensors anyway, cheap and simple to do.

Do you mean the engine speed sensor (G28) and not the wheel speed sensor? If the problem were at the wheel speed sensor, you would get an error for other modules, such as ABS and ESP.

I changed the engine speed sensor and there has been no more loss of power since then. However, I cannot confirm that I solved the problem, which is why I didn't reply. First of all, I will test it, and after 3,000 km, I will be able to say whether I have solved the problem.

5 minutes ago, primozb2005 said:

Do you mean the engine speed sensor (G28) and not the wheel speed sensor? If the problem were at the wheel speed sensor, you would get an error for other modules, such as ABS and ESP.

I changed the engine speed sensor and there has been no more loss of power since then. However, I cannot confirm that I solved the problem, which is why I didn't reply. First of all, I will test it, and after 3,000 km, I will be able to say whether I have solved the problem.

Good point! I should have photographed the lights that came on, I could be barking up the wrong tree!!!

In my case, I didn't receive any error messages and the log file was empty. If you have a screenshot of the error, that would be very useful.

Good news, after 3000km no loss of power.