HVAC air quality sensor problem

[MikkiJayne]

Originally Posted by HPsauce

Is there a recommended method for dealing with these seized screws/bolts on the ECU cover?

Are they just spinning? If so, force the lid open while turning the screw and it will pull the threaded insert out of the lower box. The trim will have to be forced out unfortunately. A bit of 3-in-1 / WD40 under the washer can help it come out without destroying it, as long as the screw isn't too tight. If they spin, it can probably be recovered.

Depending on how badly corroded the screws are, sometimes they can be loosened using mole grips on the insert once the lid is off. Worst case drill the heads off. I replace the factory inserts with M5 D nuts like these and fit new screws.

[HPsauce]

Originally Posted by MikkiJayne

I replace the factory inserts with M5 D nuts like these and fit new screws.

Excellent advice MJ, many thanks.
Found them on Screwfix, though these are M6 not M5 if that matters: https://www.screwfix.com/p/insert-nu...-50-pack/59937

[MikkiJayne]

M6 are too big - there isn't enough plastic in the box to hold them. There are plenty of M5 versions on ebay. I drill the original holes out to 8mm before fitting them. If you're replacing the screws I'd go for something 5mm longer than the originals as the threads are recessed in to the D nuts slightly. The original screws will just catch, except where the HVAC sensor is - you definitely need a longer one there.

[HPsauce]

Wonderful advice, many thanks. You've been there, done that and are an invaluable fount of knowledge.

[HPsauce]

Made some surprising progress today.
As it was fine and sunny I decided to have another look and potentially remove one of the bolts to check exact dimensions.

I removed both the middle 2 in the end and saw that under one of them was what looked like a partial washer. Realised quickly that was the sensor fixing and it was now loose!
Decided to prise up the clips on the front edge to peek underneath and the innermost fixing of the panel actually popped out undamaged! The jammed screw there was actually undone just enough to let the panel slip out.
With only the outer screw left holding it the panel is easily flexible enough (quite rubbery at the outer edge) to lift up and get at the sensor.

I took the sensor off and indoors to look at it. Saw debris under the little 2-hole cover and managed to blow it out. Then decided to see if the little cover was removable as it looked like it was. It just prised off easily and I found yet more debris inside, cleaned it all out with a clean dry artists brush and clipped it back on.
Finally I took my Dyson to the space under the panel, it was full of plant debris! And I also remembered to clean the underside of the panel itself as there was loads of stuff there too. Put everything back, that's quick and easy.
The two dodgy bolts can wait for another time; I currently have no need or desire to get into the ECU box. And if the sensor is still faulty I know I can get another and replace it easily enough now.

I don't know how the sensor works so apart from brushing away debris didn't touch any surfaces and definitely no solvents. Does anyone know what the principles of it are?

[HPsauce]

Originally Posted by HPsauce

I don't know how the sensor works so apart from brushing away debris didn't touch any surfaces and definitely no solvents. Does anyone know what the principles of it are?

I guess not, and any amount of "googling didn't throw up an answer either.

But my cleaning efforts seem to have been rewarded so far as this error has not come back:

Originally Posted by HPsauce

01592 - Air Quality Sensor (G238) 57-10 - Electric Circuit Failure - Intermittent

In fact today I had a totally clean VCDS scan, apart from the inevitable low alarm battery warning.

[steamship]

Originally Posted by HPsauce

I guess not, and any amount of "googling didn't throw up an answer either.

How about the following PDF, starting from page 6?

https://iopscience.iop.org/article/1...1/1/012033/pdf