Lean to rich sensor threshold voltage(constant)

Finnish MOT test is near and it is time to do something about Engine light. I read the fault code(not with VCDS) and it said: Lean to rich sensor threshold voltage(constant).

It would be nice to think that I have broken sensor. But I have no fault code. Has someone experienced this? Is it Lambda?

I was not able cleat the fault so I have presume that fault is on all the time.

Knowing what I do about lambda/oxygen sensors it's not about whether they are high or low voltage, its's about the speed of change from one state to the other. Typically they vary from 0-1v, but the key point being 0.5v which triggers the ECU to know whether the engine is running rich or lean. So a constant voltage is a bad thing and could lead the car to run either rich or lean depending upon the design and the failure state.

I was thinking that I have 4 probable causes.
1. Air leak for too lean (this is tested not to be the cause)
2. ECU problem for too lean or rich.
3. Sensor problem that causes too lean or rich.
4. Faulty sensor which believes that it is too lean or rich.

Now I just need to know which sensors to start with....?

Under all of those circumstances except one the oxygen sensor voltage would still vary at time, e.g. startup. The fact that the voltage is static is causing the ECU to tell you that is the fault - 99% you have a faulty oxygen sensor.

Blast from the past

How was this resolved back in the day? I've been getting the same thing slowly – not every time I start but...

My car is 1.6 FSI (2004) and I just replaced the coolant temperature sensor, fuel pressure sensor, fuel pressure regulator and also fuel filter. But I guess this no help for this. Coolant temp looks a little high + car runs just after start about 1500 RPM but only for a moment and then it's settles.

@Pepe75 Was it an oxygen sensor/lambda sensor? I'm trying to start somewhere and identify whether this is a big or a small problem
I was thinking about Pro Boost for my ECU, it might help and this would be a good reason to buy it quickly.

Thanks!

In attachments (Sorry no VCDS):

• Noncontinuous monitors: Readings from Vgate iCar Pro OBDII / Car Scanner app (Audi OBD-II / EOBD).
• Distance travelled in the readings about 6.2 km / 3.85 miles.
• No error codes.

A VAG specific scan is what you need.
I think your looking at the result of a problem, and trying to work backwards, to the problem.
Start with the problem, (which only the appropriate scan will identify). About 10 Euros for a lead, any old laptop, and your on the way.
Mac.

I will do this thanks for the help.