Exhaust Gas Recirculation EGR System Hack on 1.6TDI engines

By on January 27, 2017
egr system circuitty










Today I will discuss about a very common problem on now day’s modern car’s so called Exhaust Gas Recirculation system or in short EGR. I got a Skoda Octavia II 1.6TDI-CR engine code CAYC which was suffering on power leak, service mode or LIMP mod however, “Check engine” was on etc.

Mechanics told to the customer the EGR system should be changed, but that is a very expensive story for the customer. Then they told does some “hacker” should the EGR system disarmed ( so called EGR OFF method ) from the system so that system would no more be in an active working condition, but the error code would never be logged by the ECU etc. In my meaning that technicians only part changers and not pros.

I decide to check what is going on and why should somebody turn off a system in a car if some manufacturers are made that for some reason.

So, here is the repair stuff by me:

The EGR system on this type of engine is not as complex as it looks like. Here is a picture and a *design view of the unit.


car egr system hack

On this engine a P0408 DTC was set, which means on a simple language the EGR valve is too much closed, or in technical meaning the signal to the ECU is very low actually it is out of range.

What this mean, on this unit the common DTC’s are:

P0408 – signal too low, out of range

P0403 – signal too high, out of range

P046C – which means the EGR valve is not in a position in which it should be.

Please note that I declared these errors on a very low level so people who are not pros or technicians can also understand what this DTC’s means.

In profession technical doc’s these DTC’s are more specific and precise declared.

Here are the pin outs of the EGR connector:

Pin 2 and pin 6 are the PWM wire who powers the DC motor, where pin 2 is GND, pin 6 +12V.

Pin 1, pin 3 and pin 5 are the signal pins.

Pin 1 is the reference voltage from the ECU and the value must be 5V.

Pin 3 is the signal ground

Pin 5 is the EGR valve position value which must be between 0.71V and 4.01V.


0.71V means a closed EGR valve.

4.01V means an open EGR valve.

Everything between 0.71 and 4.01 is the position of the EGR valve which is returning to the ECU.

Checking the EGR for electronic failure:

  1. Let the EGR unit on the car as is.
  2. Check the pin 2 and pin 6 with oscilloscope for 12V PWM signal until the car key is turned to ignite position but don’t crank the engine.
  3. Check with voltmeter the pin 3 and pin 1 for 5V until the car key is turned to ignite position but don’t crank the engine.
  4. Check with voltmeter between pin 3 and pin 5 for 0.71V – 0.9V until the key is tuned to ignite position but don’t crank the car.
  5. Unbolt the EGR motor and check if the valve is moving freely by turning the half gear by hand.

how to hack egr system

In my case in the ECU was stored the P0408 error code.

Until I checked the signals as I wrote I realized does the signal between pin 3 and pin 5 are low which was around 0.59V. This triggered the DTC error P0408. There were also no trapped mechanical parts or even no clogged parts.

Why have I a low voltage in a zero position of the EGR valve?

I assume because the age and millage of the car. The mechanical parts got some space after years of friction and this would explain a small deviation in the voltage. I have to get back a 0.71V to the ECU when the EGR valve is in zero position.

What I did was actually make a small voltage divider with two resistors and sum that voltage with the output voltage which tells the ECU the position of the EGR valve. In my case, I measured a voltage of 0.59V but I need 0.71V. So I must add something around 120mV.

I have a reference voltage of 5V on pin 1. Adding two resistors in series so does it gives me in the midpoint a voltage of around 120mV. Then I cut the trace on the PCB where the output pin was. Now one end of the resistors was soldered to the pin +5 and the other end of the resistors was connected to the pin5 on the IC. The midpoint of the resistors was connected to the ECU or to the pin 5, so I got a new value to the ECU which was around 0.72V.

Here is a picture about my hack.

how to fix car egr system

Actually I summed the two voltages and so I got a desired voltage around 0.7V.

What you have to worry about this hack is that, does the value of resistors what I used is not specified to all situation on all EGR problems.

To specify the value of the resistors you should first check the difference in the voltage between the measured voltages on the EGR connector pin 3 and pin 5 and there must be a voltage which is 0.71V.

I also tested this on two other cars with the same symptoms and all of them had a lover voltage but not the same low voltage. One of them had around 300mV the other had around 630mV etc. and in relation of the differential you have to calculate value of the voltage divider with two resistors.

Before I made this hack, I simulated this also on my computer in my favorite circuit simulator. NI Multisim, of course there are other nice simulators too. Here is my simple’s circuit from my simulator:

egr system circuit simulator

Here is the formula for calculating the voltage divider resistor values:



Vout = should be the searched voltage which is 0.71V

This tutorial will save money for the customer and lot of repairing time for the technicians who repairs the car, but you should know does, this type of repairing is not usable and without success if the EGR system is full filled with dirt and if they are some failed mechanic parts and the EGR valve mechanism can’t move freely. In that case you have to change the mechanic mart too.

* The design view picture was taken from the SSP 442 training document made by VW AG.

I hope you enjoy this tutorial and will save lot of repair time.

This article was prepared for you by Christian Robert Adzic from Novi Knezevac-Serbia.

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  1. Bulent NUR

    January 27, 2017 at 5:45 pm

    So many thanks.

    • Andrew F. ali

      January 30, 2017 at 11:37 pm

      GOOD JOB!!!....I don't know much about Auto-electronics....but reading your article...I feel a great sense of appreciation for your work. Thanks.

  2. Albert van Bemmelen

    January 27, 2017 at 6:01 pm

    Thanks Christian, you've moved from Eeprom hacking to Car hacking. Very Impressive!
    I do not own a Car nor a OBD device, so it is all unknown territory to me. But your information could always be of use to someone I know who fixes cars.

  3. Ulises Aguilar Pazzani

    January 28, 2017 at 10:04 am

    Mr Christian , happy New Year , nice repair something new great

  4. Parasuraman S

    January 28, 2017 at 1:46 pm

    You have the deep knowledge that of a Design Engineer! Why don't you make a data bank of such common electronic problems in cars and develop a replacement kit which can replace the defective circuit with minor modifications? You can not only earn but also help car owners from spending heavy amount on expensive replacement of its whole unit in place of minor rectification that set it right!

    • Chris

      January 30, 2017 at 7:05 am

      Thank you for your support my article.
      You know, I've thought about it to make such of data bank with nice replacement kit's but that would be very hard to make it universal.
      I also found some "universal" replacement kit's on the internet from some
      peoples who sale it but that won't actually work in many case, but in some situation that would work.
      Lets say, in the situation of this article, I would never know what voltage divider I should make for the customer until I know what is the output voltage of the positioning IC. In that case I would sell the customer a not working part. The customer would not be happy.
      But! I think, if I release documents about the problem, with facts on blogs like this thanks to Mr. Yong and other blog holders, the mechanics and electronic technicians could read and implement it and make the customers happy.
      I earn lot other ways from articles like this, because it is in front of eyes of the readers of the whole word, and people can check my writing and comment it. Until I get positive feedback from all of you I know I earned more then money, I earned reputation and I now I done my work in a good way.
      Some times the customers of the car and who would be a potential buyer of my kit's should have some knowledge about electronic and information technology so he could make a measurement and made the repair...
      But of course your idea is well come by me and I'm always thinking about how to make that replacement kits user friendly and working.

      Thank you for your time.
      My best regards.

  5. Yogesh Panchal

    February 1, 2017 at 4:56 pm


    Thanks for informative article

  6. Miguel

    February 6, 2017 at 2:36 am

    Excellent note, it will serve to do the same to my hue (daewo) that has the fault P1403, already cleaned the valve and continues with the same error, thanks, greetings.

  7. ombra32

    February 23, 2017 at 8:07 pm

    Very impressive!! Like always...

  8. Siavash

    August 31, 2017 at 9:25 pm

    You are a legend ive been looking for this information all over the Internet for a month now so i can do this. Where did you find this information about the reference voltage and minimum and maximum values?
    Thanks alot salute from new zealand

  9. SEAN

    January 19, 2018 at 5:53 pm

    Hi great right up. Can you tell me if I have 0.04v between pin 3 signal gnd and pin 5 signal what mv of resistos do i need for each pin

    • Chris

      January 30, 2018 at 1:59 am

      Thanks for supporting my article.
      So, for first.
      Please let me know what voltage you need?

      If your egr is another type or another type of car, maybe your voltages are different.
      So, you need to figure out what voltages are your min and max.
      Also you must need to know what is the cos of your fault...

      My best regards.

  10. Ľubomír Baran

    February 7, 2018 at 8:24 am

    ***Vout = should be the searched voltage which is 0.71V

    This is not good... i guess this Vout should be 0,124 what is yours added voltage. Or formula for 0,71=V2*(R2/(R1+R2)) + V1; for your picture. Am I right?

    But appreciate this really helpful article, it helps a lot.

  11. Paul Doe

    November 16, 2018 at 2:26 pm

    Hello. I got error P0403, replace the old EGR motor only(wahler) with one newer(but second hand - BorgWarner) and now I got error P046C. It is possible to be a hardware problem with my EGR? I checked voltage wit VCDS, and the old one(with P0403) has values between 0.9 and 3.4, and the new one has values between(1.2 and 3.9). I dont know what to belive... And it is difficult to change the entire EGR system, because its location is not easily accessible.
    Any opinions?


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