MicroHacker Forum

Hello, lately I am experiencing issues with EGR (MK4 2011) which is causing DPF to regen too often. My current solution is that I have mounted second EGR to the engine bay and connected it to car so the PCM controls the valve of the second EGR and thus the original EGR in the car remains closed. The DPF regens returned to normal (from 50 to 500km).
What I would like to do is replace the second EGR with small circuit that will tell the car what it wants to see - position of the valve.

I have found an emulator here https://maker.pro/forums/threads/help-t ... 193/page-2 but after testing it does not work properly as it shows 2.8V all the time which is about 50% open. I have measued voltage from the EGR sensor and when it is closed the sensor reads 0.7 V and when it is open (engine idle) it reads 4 V.
The valve is probably controlled by PWM but I do not have tools to measure that, only thing I can tell is that when the valve is open the electric motor has 2.3 V and when it is closed 0.5 V
Below are the inner parts of the EGR, the valve position is probably determined based on a magnetic field as the square thing inside the spring changes angle.
Can anyone help?

Yes, the shown chip is an integrated Hall-Sensor HAL815A. It is driven by 5V operating voltage and outputs a linear voltage from usually 1-4V. The voltage depends on the distance of a megnetic part located somewhere on a gear mounted at the valve.

The motor is driven by a PWM Signal, which gives him speed and direction to turn. I guess the ECU set's a PWM and expects the linear voltage of the Hall to reflect the movement. If that is not witihn given boundaries it's might raise an MIL oder internal error.

The schematic you shown will convert a PWM signal into a linear voltage. It should pick the PWM signal for the motor and answer with a voltage. As the motor might be driven with higher voltage than the sensor output, the schematic uses the isolation approach with the transistor. So far, so easy.

I think the magic is to justify the parts so they give the right voltage answer to the right PWM input. You would need a least a digital oscilloscope to find out the PWM frequency and pulse-pause ratio.

But it should be sufficient to measure the voltage out of the Hall at different closing/opening angles from full closed to full open first. This might simply be done by providing the power supply to the Hall and turn the valve by hand?
Once you get that you might be able to attach the electronic and mease it's output and compare it with your measuremts. Then play with capacitor and resistor until you get the desired voltages.

I have already measured the voltage from the Hall sensor as I have wrote it in the first post but only for the fully closed and fully open state.
Closed is 0.7 V (0% in forscan) and when it is open (engine idle) it reads 4 V (90% in forscan).
As for the PWM driven electric motor I have measured 2.3 V when open and 0.5 V when it is closed but with only simple multimeter.

I have also build the circuit from the schematic but after connecting it to car it shows 2.8V all the time so car thinks that the EGR is stuck.

I have managed to get a pictures from a borrowed oscilloscope but dont know how to apply the values to the circuit.
First one is fully closed and second is fully open (engine idle).

If you want the EGR to be closed all the time you can replace the intake air temp sensor (is located inside the MAF just efter air filter)with a 5 K ohm resistor , if the PCM detects a temperature below 6 degrees then EGR is always closed (if you have a 2.0 , the 2.2 may require different value).
See this instruction I have made in another forum : https://www.talkford.com/threads/low-mp ... st-3204842

Thanks for the tip. I might try that (I have 2.0 120kW)
Although I have Webasto installed so I am feared of the constant heating during driving as you mentioned in the thread. Do you really know that the PCM is signaling the Webasto to turn on and is based on the intake air temp? I always thought it is based on outside temp.
I will test the Webasto thing when there is above 5°C outside.

So I have tried it with 6.5kOhm which is showing -3°C as intake air temp and EGR is indeed closed.
Webasto did not turn on while driving as outside was 10°C which is good. This means it is controlled by outside temp instead of intake temp.
Hovewer I will keep monitoring.

I can confirm that the mod with air temp works perfectly. Webasto is on only when outside temp is below 5°C so everything works correctly.
Thanks for the tip.

In my opinion, unnecessarily complicated work, it can cause other problems, the easiest is to modify the ECU map

Can you point me how? I do have chinese Kess V5.017 but want to keep DPF intact, only delete EGR.