Audi SQ5 8R 3.0 BiTDI – SCR inducement/countdown remains, very low AdBlue quantity from dosing valve despite ~5 bar pressure

VCDS
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Hello,

I am currently troubleshooting an SCR/AdBlue problem on an Audi SQ5 8R 3.0 BiTDI (240 kW / 326 PS).

I would appreciate some help interpreting the VCDS results, especially the SCR dosing quantity test.

Initial problem

The vehicle had an AdBlue/SCR warning with a no-restart countdown in the instrument cluster.

P207F – Reductant Quality Performance had previously been stored.

There was also a fault concerning the downstream NOx sensor (NOx sensor 2, bank 1).

The downstream NOx sensor has since been replaced.

At the moment P207F does not return and there are currently no relevant engine DTCs, but the AdBlue no-restart countdown remains in the instrument cluster. The last displayed remaining distance was approximately 70 km.

Work already carried out

  • AdBlue tank cleaned
  • AdBlue pump replaced
  • Pump/seal components replaced
  • AdBlue dosing valve removed and cleaned
  • Crystallised AdBlue deposits around the dosing point removed
  • Downstream NOx sensor replaced
  • Fault memory cleared several times
  • SCR system adaptations/basic settings investigated with VCDS

SCR lock reset

I performed:

IDE04730 – Reset SCR lock

VCDS reported that the routine completed successfully.

However, the no-restart warning/countdown in the instrument cluster remained.

SCR efficiency test

I also tried:

IDE04732 – Check of SCR efficiency

The engine was warm and the test was allowed to run for more than 30 minutes.

During the test the glow plug/heating indicator was continuously active and the ECU controlled the test, but the countdown did not disappear.

I have not yet obtained a clear successful final result which actually removes the inducement.

SCR pressure / actuator test

During the SCR dosing valve actuator test the following values were observed:

  • Reductant pressure: approx. 4,970–5,000 hPa
  • Pressure remained very stable around 5 bar
  • Pump activation: approx. 50 %
  • Pump speed: approx. 1,900 rpm
  • Dosing valve resistance: approx. 12.5–12.7 ohm
  • Dosing valve holding current: approx. 0.46–0.50 A
  • Dosing valve saturation current: approx. 0.94 A

During the dosing quantity test the system pressure also reached approximately 5.3 bar before stabilising around 5 bar.

Therefore the pressure generation itself appears to work correctly.

IDE02636 – SCR metering quantity test

This is where the result became interesting.

I removed the AdBlue dosing valve from the exhaust but kept:

  • electrical connector connected
  • AdBlue line connected

I then performed:

IDE02636 – SCR metering quantity test

Although the SCR system had approximately 5 bar pressure, only a very small amount of AdBlue / only a few drops came through the dosing valve during the complete test.

The valve does not appear electrically open-circuit and the pressure upstream is correct.

The dosing valve fitted to the vehicle is:

■■■: 4H0 131 113 A

Test with dosing valve disconnected from the AdBlue line

As another diagnostic test I disconnected the AdBlue line directly at the dosing valve and repeated the test with the line aimed into a container.

In this configuration, a clearly larger amount of AdBlue came directly from the supply line.

VCDS subsequently aborted the routine for safety reasons, which I assume is understandable because the hydraulic circuit was open.

This makes me suspect that the restriction is inside the dosing valve itself rather than in the pump or supply line.

My questions

  1. Does the combination of approximately 5 bar SCR pressure + good supply from the open line + only a few drops through the dosing valve strongly indicate a restricted/defective N474 dosing valve?
  2. Does anyone know the specified quantity in ml for IDE02636 – SCR metering quantity test on this 3.0 BiTDI application?
  3. Could an under-dosing valve cause P207F / insufficient SCR efficiency / AdBlue inducement countdown, even if P207F is currently no longer stored?
  4. After replacing the dosing valve, what is the correct VCDS sequence to release the no-start countdown?

For example:

  • clear DTCs
  • reset SCR adaptations/tank level if necessary
  • IDE04730 Reset SCR lock
  • IDE02636 metering quantity test
  • IDE04732 Check of SCR efficiency
  • road test
  1. If a new dosing valve produces the correct quantity but the inducement still remains, would you investigate the SCR catalyst efficiency / NOx values next?

I have VCDS logs from the dosing test, photos/videos of the spray test and a complete Auto-Scan available and can post them.

Any advice regarding the correct test sequence and expected dosing quantity would be very helpful.

Thanks!