Volkswagon Polo 1.6TDI 6R1 year 2010 idling problem solved

By on June 27, 2015
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I got a call from a local car-repairing garage.They asked me to come to the workshop and see what can I do with the car, which has an idling problem, but they cannot figure out the problem.

When I started the engine, I could hear a very unusually sound and the engine was shaking, as some of the cylinders are misfiring or so and the “Check engine” indicator was on. The shaking happened only on idle state of the car or when the car was driven on a low RPM. When I go for a test drive, I cannot figure out any other problems, only the sound, shaking and the shining “Check engine” lamp.

I connected my VCDS diagnostic equipment, and start to read the fault code from the car. I saw a DTC ( Diagnostic Trouble Code ) error number P0183 which mean something is wrong with the fuel temperature sensor on the car.

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Diagnostic reading result.

The fuel rail/system pressure is an old error but not deleted before. Do not pay attention to that. Let see how this little parameter and sensor works together with the ECU ( Electronic Control Unit ) of the car. And how they affect the idle state of the car.

The fuel temperature sensor on a vehicle is an important part in the meaning when the vehicle has to driven on a low engine revolution stage or the engine is on idling stage. This component gives the ECU the information together with the coolant temperature sensor about what is the temperature of the fuel and coolant liquid. In addition, this two measuring plays a very important rule in the creation of fuel mixture ration. Based on this signal, the engine ECU increases the fuel injection volume to improve drivability during low engine resolution and high fuel temperature.

Here is how this thing works.

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A thermistor built into the fuel temperature sensor changes the resistance value according the fuel temperature. It is actually a variable resistor, which changes his value according the temperature.  The fuel sensor is connected to the ECU. The ECU power the sensor with 5V DC voltage and measures how much voltage is on his input pins. From this value the ECU calculate the temperature value.

These diagram shows where is the acceptable value of  Res./Temp. These together act like a voltage divider as you can see in the next picture.

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Here I made a small simulation of the circuit with my favorite Multisim software to demonstrate how the fuel temperature sensor and the ECU work as a team.

As you can see, the R3, R6, and R9 are the thermistor in the sensor. The Probe1, Probe2, and Probe3 are the input voltage into the ECU. I must say all other parts, except the sensor thermistor, are integrated into the ECU.

Therefore, you can see how the value of the thermistor affect the input voltage in the ECU and the ECU make some setups during the driving or idling the car.

Here is the schematic of the exact car what I repairing.

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Can you remember when I told, you should remember the G81? Here is it. The G81 is the fuel temperature sensor and the G62 is the coolant temp sensor. They are connected to the ECU J623 through the T60/43, T60/54 and T60/42 connector on the ECU. 

T60/42 means – Connector whit 60 pins where the exactly wire is connected on the pin 42.

If you disconnect that connector and connect your multimeter to pin 42 and other end to T2/2 on the fuel temp. side then you can measure for a resistance or a broken wire or what you need.

Ok, enough about theory, lets see how you can check all this stuff in a real situation.

Checking the sensor and the ECU:

Step

  1. Check the resistance of the sensor on the two terminals. From the diagram on the Fig1 you can calculate what temp is your fuel and then start the engine, wait a few min. and check again. You should get a greater temp measuring and a lower resistance.If this is not the case, then your sensor is faulty. Replace the sensor.

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2. Disconnect the plug from the sensor. Check the two wires with the multimeter for 5 volt, with ignition on. If you have, no 5V or the voltage is greater or smaller then the reference voltage, which is 5V then, you have shortened, broken wire or maybe the ECU is faulty.

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I figured out does I have exactly 5V on the terminal plug from the ECU. I have too a good sensor but the car still have a worse idling. But! when the plug was disconnected from the fuel temperature sensor then the engine was quiet. I decide to make another check, with a potentiometer connected to the plug from the fuel temperature meter to the ECU.
I connected a 5K potentiometer to the connector and still connected my diagnostic equipment to the vehicle, found the channel where was the reading of the fuel temperature.

Then I asked a person to move the potentiometer from left to right side and back.

With this method I got the information does the ECU measures a temperature value. Yes, he did it but the ECU has a faulty measuring range. The resistance of 30C was around 240Ohm on the potentiometer. And this means the ECU is faulty or the software in the ECU is out of calibration or whatever…

You have 3 solutions:

  1. Try to repair the ECU
  2. Change the ECU
  3. Delivery a fake temperature to the ECU

I asked the owner of the garage what should I do?

They told me after he talk to the owner of the car I should use the solution 3. Ok, I disconnected the fuel temperature connector, and put a 100 Ohm resistor into the two wires terminal and wrapped it whit electrical tape. After this repairing, I checked for trouble codes recorded in the ECU and cleared all of them.

Started the car and go to a test drive again. The check engine indicator did not fire up again. I checked in the garage if there is still a DTC error code on the ECU recorded, there was no DTC errors recorded. The car was nice idling and was driven well. This is not the best way in which you can repair the car, but if you have no option then this will help you to solve the problem.

This solution won’t harm the car electric or mechanic system but, if you put a trimmer and play a bit with the setup of the trimmer then you can get out a bit more power from your engine. So to say, you have made a bit tuning on your vehicle.

christian

 

 

 

 

 

 

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

Please give a support by clicking  on the social buttons below. Your feedback on the post is welcome. Please leave it in the comments.

P.S-  If you enjoyed reading this, click here to subscribe to my blog (free subscription). That way, you’ll never miss a post. You can also forward this website link to your friends and colleagues-thanks!

You may check his previous repair article below:

http://www.jestineyong.com/blaupunkt-vw-gamma-repairing-unlocking/

 

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22 Comments

  1. Robert Calk

    June 27, 2015 at 3:58 pm

    Good job Christian. I'm sure that they suspected the throttle position sensor first.

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  2. Albert

    June 27, 2015 at 4:12 pm

    Thank you Christian Robert for this article on repairing a strange ECU malfunction on the 2010 VW Polo. Changing the ECU will be rather expensive but could confirm that the ECU is the problem. I take it the owner does not have any Buyer Guarantee left for the Garage to exchange his unit for free? A friend of mine also has a VW but he drives a Passat. On his ECU unit there were 2 wires coming out that are uncertain were they are for. Marters had bitten through this ECU cable so badly that this 2 wire cable had to be removed to prevent any short circuiting resulting in Fire. Since my friend still doesn't know what function this cable was going to the inside of his Motor Block your article with using the VDS Diagnostic Device could prove very usefull ! Maybe you can tell a bit more on were to buy this device and what type it is exactly?
    Albert.

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    • Chris

      June 29, 2015 at 2:08 am

      Thank you Albert for your complement.
      You can buy the VCDS diagnostic tool from Ros-tech: http://store.ross-tech.com/shop mine is from them but it is an old one. Now days I use the Autocom diagnostic tool because I have didn't repair only VW,Audi,Skoda and Seat and VCDS is only usable on VAG group of cars.
      You can buy a good copy of Autocom or Delphi diag tool from china manufacturers.
      I suggest you to buy the cheaper Delpi or Autocom from China.

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  3. Kassim Ali

    June 27, 2015 at 5:25 pm

    Thank you very much Mr. Adzic for this article, it motivates me to check on my VW Bora 2002 model manual gear because i am facing some problem in the cooling fans both are only working in high speed and the water sensor in the thermostat is damaged and i have no wiring diagram beside i have replaced the fan control relay but still the problem there. I believe that your explanation really encouraged me to do more check.can you help me to get the diagram please?
    with my best regards and thanks
    Yours faithfully
    Kassim Ali

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    • Chris

      June 29, 2015 at 2:15 am

      Hi!
      Of course I will help you.
      Can I get your E-mail and I will send you the schematic if I found one for your car.
      My best regards.

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  4. Gary

    June 27, 2015 at 6:26 pm

    Very interesting repair Christian you are obviously a pretty good engineer.

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    • Chris

      June 29, 2015 at 9:16 pm

      Thank you very much.

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  5. mustabz

    June 27, 2015 at 7:49 pm

    Brilliant article and great craftsmanship! Congs

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  6. Gerald

    June 27, 2015 at 8:40 pm

    Hi Christian,
    Nice story and well explained. It shows your excellent understanding of the circuits and how the whole thing is working. Well done!
    Regarding the fix I would have a couple of concerns. It is OK as a temporary fix but I believe that the ECU should be either fixed or replaced. I would worry about two possible scenarios:

    - Someone in the future might replace or repair the ECU because of another problem. The ECU will then think that the fuel temperature is over 100 degrees as this would be the temperature corresponding to the 100 Ohm resistance. Well I suppose the technician would figure this out and find your resistance, then reconnect the sensor…

    - The ECU problem could be caused by a decaying component that might not stop here. Who knows if in a couple of weeks or months the ECU will need a 50 Ohms resistance to believe that the fuel temperature is within normal limits? Then the alarm would come back.
    Well I don’t know much (or close to nothing) about automotive electronics. This was just a thought. In any case I enjoyed the article, thanks for sharing.

    Cheers,
    Gerald

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    • Chris

      June 29, 2015 at 2:22 am

      Thanks for your comment Gerald.
      Everything you wrote is ok and you are alright but, the owner of the vehicle is the man who pay and he/she have to choose between option 1, 2 and 3.
      But! I agree with you of course.

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      • Thabiso

        November 22, 2016 at 1:37 am

        Good Day Chris, im having a big problem with my 2010 polo 1.6 TDI, it refused to start, I took it to different people and the last one said the problem its computerbox and im trying to find second hand 1 but the 1 i find it got different part number and the one i have they say it cant be repaired

        So my question is if computer boxes have different last number 2 letters will that work on my polo?

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        • Chris

          January 4, 2017 at 7:59 pm

          Şory, but that would not work only with changing the computer box.
          Can you share some more infos about the diagnostic reading result or even the DTC (Diagnostic Trouble Code) numbers?

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  7. mabrouk

    June 27, 2015 at 9:07 pm

    very nice work, thankyou very much Mr. Adzic

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  8. Mark

    June 27, 2015 at 9:09 pm

    Hey Christian,
    Job well done! Using scan tools are invaluable now-a-days as the technology has advanced so fast. I use a G-Scan myself, which is a generic one based on a Hyundai model. An excellent tool!
    Sometimes money limits the results of a repair, but you have done a good job by keeping the ECU within perimeters, so that it doesn't log a fault code. Unfortunately, without a variable resistance the ECU will not be able to set up the correct Stoichiometric ratio and vary it through the 'look up' tables.
    However, you have used a good knowledge of the components and the system to work around a tricky problem.
    Congratulations!

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    • Chris

      June 29, 2015 at 2:34 am

      Thank you Mark for your comment.
      I agree with you. The best way would be to repair the ECU or to change it.
      But... you know.... 🙂

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  9. Anwar Shiekh

    June 27, 2015 at 9:22 pm

    I am a friend for using silicone oil on electric connections, and am still amazed at how many problems it can solve, not only in the car, but also electronics. I also recall one guy who replaced the capacitors in the ECU of a badly running engine.

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  10. Yogesh Panchal

    June 29, 2015 at 2:12 pm

    Thanks for informative article please keep sharing.

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  11. Humberto

    June 30, 2015 at 9:41 pm

    Hi Christian Robert Adzic, good articles, photos and explanation.. Keep up.

    Likes(1)Dislikes(0)
  12. Debirt Maynard

    July 2, 2015 at 4:15 am

    Excellent Chris!!! Sometimes what you do is limited by what the client is willing to pay at the time of repair. Replacing the faulty ECU is strongly recommended however.

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  13. Meizi

    July 5, 2015 at 9:04 pm

    Job well done Chris, to find the cause of the DTC is already an expertise, with a wide knowledge in electronics make the difference.Good job Chris.

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  14. Hendrik

    September 22, 2017 at 5:10 pm

    Nice article. I just a have a quick question. You say this: "you can calculate what temp is your fuel and then start the engine, wait a few min. and check again. You should get a greater temp measuring and a lower resistance.If this is not the case, then your sensor is faulty". Why would the fuel temperature increase? Surely the fuel is coming from the fuel tank and should stay the same temperature even if the engine has been running for a while.

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  15. Paul

    November 17, 2017 at 4:45 pm

    I have the same problem and connected a 100 ohm to the connector but I'm not getting any power out of the motor when it's connected
    If I pull the bridge out it has normal power
    You can drive the car normally when it's not connected but I get a check engine light on as soon as I connected the plug back in it starts to shake

    Any help please

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