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-   -   DIY: Diagnosing and repairing Automatic Headlight Fault in my Skoda Octavia (https://www.team-bhp.com/forum/diy-do-yourself/277401-diy-diagnosing-repairing-automatic-headlight-fault-my-skoda-octavia.html)

Problem statement:
I bought a used a 2016 Skoda Octavia 2.0 TDI DSG about 1.5 years ago. Ever since I bought the car, if I put the headlight switch to Auto, I would get an error on the MFD and infotainment - Fault: Automatic Headlight control.

The headlights would light up even in broad daylight. If I put the wipers in Intermittent mode, they would start and keep wiping even if the windscreen was bone dry. I knew about this fault before I bought the car. I raised this concern to Skoda A.S.S during the paid pre purchase inspection that I got done on the car. Skoda A.S.S said it was due to aftermarket HID and LED bulbs that the previous owner had gotten installed on the car.

Troubleshooting:
I believed what Skoda A.S.S told me. After I purchased the car, I decided I will revert to the factory halogen setup. I even tried replacing both the low beam HIDs with H7 halogen bulb, but even then, I would get a Automatic headlight fault if the switch was on Auto.
I then got myself OBDeleven to look at the actual error that the car was throwing. The error was "Rain/Light recognition sensor No communication" Fault code U10F600.


After looking at the error, I searched on the internet but I could hardly find anyone who had an error similar to mine. But I got a hint on obdeleven forums, that it could be a faulty sensor. I again approached Skoda A.S.S and asked them if it could be that the rain and light sensor be faulty? Skoda A.S.S again said that the fault was due to the aftermarket headlight bulbs. I knew that either they were not intereseted in investigating the fault or they did not know what was going on. I had to solve the problem myself.

The error stated, that the Central electrics module or the BCM was not able to communicate with the rain and light sensor. The possible problems could be:
1. Faulty rain and light sensor
2. Blown fuse to rain and light sensor
3. Cable not plugged in either at the rain and light sensor or the BCM end.
4. The cable itself is damaged

I saw some youtube videos on how to get to the Rain and light sensor. It involved removing the IRVM. I removed the IRVM and inspected the rain and light sensor connection. The cable itself had 3 wires and the connector seemed to plugged in securely.
The wiring loom for the rain and light sensor has 3 wires. Pin 1 (Red and white) for 12VDC, Pin 2 (Brown) for earth and Pin 3 (purple and white) for LIN communication (Communication with the BCM).


I then proceeded to check the +12V and ground using a multimeter. Pin 1 was receiving 12VDC with respect to ground. Hence a blown fuse was ruled out. I was getting continuity between the ground wire and door hinge. Hence ground was also ok.
In order to check continuity of the wire between the rain and light sensor and the BCM, I would have to remove the wire from BCM end. According to the wiring diagram, the wire from rain and light sensor is connected to 28th pin of connector C on BCM.


Accessing the BCM is tricky because it sits behind the the fuse box behind the glove box. In order to access the C plug, I had to remove the trim on the side of the glove box and the trim of the passenger side running board. I do not have photos or videos, but I used the following video as a reference. Although the car in the video is a LHD, the location of the BCM is the same. But since our cars are RHD, the BCM is located on the passenger side for RHD cars.
https://youtu.be/Pee61VyHwYM?si=VrJLR02gC9fXm9Og

The multimeter probes were too short for measuring the continuity of the wire between the rain sensor and BCM. So, I inserted a pin on pin 28 of BCM, connected a speaker wire to the pin by twisting it on to the pin and measured continuity of the wire. I did not get continuity. This indicated that there was a break somewhere in the wire and this was the reason why there was a No communication fault.


Tracing the cable and finding the break would have been difficult since the wire is part of a larger cable loom and it seems to go above the headliner. Hence I decided it was wise to leave the wire untouched.

I did not have the pins that go inside the BCM plug and the rain and light sensor plug so I could not make a new wire altogether. So, I snipped the original wire about 2 inches from the both the ends of the plug. I used the long speaker wire to bridge both the snipped ends. I covered both the junctions with heatshrink to secure both the junctions and avoid shorting.

I tidied up the wire using lots of cable ties after tucking it above the headliner and through the passenger side A pillar. I installed back all the trims. Finally it was the moment of truth.

I put the headlight switch to Auto and I did not receive any fault on the MFD. I put the wiper stalk in intermittent position, it wiped once and did not wipe anymore. I then sprayed some water on the rain sensor and the wipers started wiping. I covered the rain and light sensor with a thick cloth and the lights came on :Cheering:

Learnings
The primary reason for writing this DIY is because I could not find the error that I was facing, even after a lot of googling. I hope that someone who is facing the same error on their VW cars stumbles on this thread. Whatever posts that I have found, blamed it on the faulty rain and light sensor. I too, was of the opinion that sensor would be bad, because why would a cable break, specially when 12V and ground cables were OK. Initially I even purchased 1 used sensor off ebay of same part number which did not work and then I purchased a new rain light and humidity sensor of different part number which also did not work. It is only then that I decided to test the wire before throwing more money at parts. I was fortunate that the sensors themselves were not very costly (30$ each) and ebay has a good return policy, but I did have to ship the sensors back and did cost me about 550 Rs each time via India post.
In hindsight, I should have checked the wires first. Given the fact that bad sensor is a higher possibility and the difficulty to reach the BCM, I foolishly decided to replace the sensors first.
It is always the little things.

Your home work looks clean and loved the way you handled the diagnosis all by yourself.

Good to see that your efforts has paid off.

Kudos to you. Happy Motoring.

Liked the way you went about diagonizing the issue. Finding the root cause of problem is half the problem solved! Glad that you resolved the issue bothering you for so long! :Cheering:

I am reminded of the quote by a very good YouTube diagnostician - Ivan Temnykh of Pine hollow auto diagnostics.

A Multimeter, a wiring diagram and common sense goes a long way in catching electrical faults.

Super job in using the implements the way they are meant to.

Good to see such DIY especially the VAG ones..
I had DIY for my preowned Yeti with Auto-switch and Cruise control, enjoyed it.

Can't quite explain it, I was filled with immense joy when I got to the moment of truth section. Being a DIY enthusiast myself (not a DIY pro) It felt like having gone through the rigors in person and finally succeeding. Thanks for sharing, especially the details !

This is a fantastic DIY and you did fix the issue.
That Skoda A.S.S. Should shut itself down.

That was a great self-diagnosing procedure. This clearly shows the attitude of some ASS dealers of Skoda where no one is ready or capable enough to sit and find the issue of an out of warranty car.

By hearing the symptoms first, I also thought it was the sensor issue. But really worried how that wiring got affected. Just curious what might have caused that wire alone to have a malfunction; might be any ant bite/corroding or some issue? Will it affect the other wires near to that area in the long run? Did previous owner tamper those areas for something? Random thoughts to think about.

Anyway, good to hear those great feature functions fine now.

Kudos to you for finding a way to make it work! clap:

In today's world, every service center is only interested in parts replacement - and no one is interested in repairing any defective part as it requires investing significant amount of effort for diagnosis and also the cost of repair may not be as high as what they could charge for replacement.

Hence their affinity towards vehicles under warranty, as owners might be extremely reluctant to replace costly parts unless absolutely necessary for out-of-warranty vehicles. This is where the FNGs thrive, as they are more willing to help the owners in diagnosis and repair instead of outright replacement for all problems.

This is true even for home appliances (like washing machine, refridgerator, TV etc) where authorized service centers recommend parts replacement whereas local technicians help to repair parts, even faulty boards and switches.

The LINBUS cable that I found non continuous, is part of a bigger cable loom which has cables for self dimming IRVM which again merges to another cable loom. Although I would have loved to find out the break, it doesn't make sense to unwind the full loom. The wire might have been broken when the windshield was replaced due to stone chip. I will never know. There were no signs of corrosion on both wire ends. Also since only rain and light sensor was not working, I hope it was a one off case.

Wonderful mate !! Lovely to see a bit of common sense debugging and the drive to look for a problem ! Inspired :thumbs up