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Volkswagon Polo 1.6TDI 6R1 year 2010 idling problem solved
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.
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.
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.
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.
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:
- 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.
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.
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:
- Try to repair the ECU
- Change the ECU
- 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.
This article was prepared for you by Christian Robert Adzic from Novi Knezevac-Serbia
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