Problems with lights after New Heater Matrix

[Xenon]

Hello all.

I’ve recently had a heater matrix replaced in my Audi A3, 2014.

The work was carried out by a garage. 
Upon collection, a warning light was on and further investigation revealed that two of the rear lights were out, the heated rear window, and the reverse lights too as well as the rear wiper. The number plate light is on, as well as the brake lights and the boot release also works.
 

The garage has since taken the centre console apart and retraced their steps to check if cables had not been connected, but all seems in order. They have checked the relevant fuses, and say that some of the fuses are directly in the ECU. 
 

They have also checked to see if there is a Technical Service Bulletin for that model, which they concluded, there isn’t. 

Does anyone have any ideas on what might be causing this issue and how to remedy it?

Thanks for you time,

Best wishes for 2024!

Edited January 9 by Xenon
Missing info… now added.

[Magnet]

Welcome Xenon,

Sorry to hear about your issue, and the garage’s difficulty in resolving it. 
Possibly too simplistic, but I wonder whether the rear end electrical issues are a coincidence, and not actually related to the work done. 
If it were mine, I would be eliminating the possibility that the issue is due to fractured wires in the flexible harness section twixt the body and the tailgate. This is a favourite place for wires to fracture after many years of opening and closing - particularly in this cold weather. Always worth an eliminating look at. Similar inspection with flexible section leading into the driver door. 
Perhaps you could let us know how they get on. 
Kind regards,

Gareth. 

[Xenon]

Thanks Gareth,

I’ll pass on this advice to the garage and see if it is something they have looked at. 
It does seem odd that when we picked it up the light was on the dash. 
I will let you know what the outcome is.

 

Many thanks for your time and suggestion.

Xenon.

[Stevey Y]

10 hours ago, Xenon said:

Hello all.

I’ve recently had a heater matrix replaced in my Audi A3, 2014.

The work was carried out by a garage. 
Upon collection, a warning light was on and further investigation revealed that two of the rear lights were out, the heated rear window, and the reverse lights too as well as the rear wiper. The number plate light is on, as well as the brake lights and the boot release also works.
 

The garage has since taken the centre console apart and retraced their steps to check if cables had not been connected, but all seems in order. They have checked the relevant fuses, and say that some of the fuses are directly in the ECU. 
 

They have also checked to see if there is a Technical Service Bulletin for that model, which they concluded, there isn’t. 

Does anyone have any ideas on what might be causing this issue and how to remedy it?

Thanks for you time,

Best wishes for 2024!

Hi I think the fuses in the ECU theory is horse manure the units are security sealed with no access for the changing of any fuses even if you had it apart, lateral thinking asks why would you put a fuse [which will fail at some point] in a secure no access shell ?, I think someone has run out of solid plausible excuses, my first port of call would be to check the bulbs and power supply to the light units themselves if everything else is working chances are the bulbs have been shorted out if they removed any wiring plugs.

[Xenon]

I like your thinking Steve, that makes sense now that you say it. I will give the garage your suggestions. Great idea! Many thanks!

[Stevey Y]

11 minutes ago, Xenon said:

I like your thinking Steve, that makes sense now that you say it. I will give the garage your suggestions. Great idea! Many thanks!

Hi no worries, have seen this before where you disconnect something and it blows something else, the wiring on all Audis is over complex but it pays to look at the simple things first, I have even had it where I had no illumination on a tail light but power coming in so replaced the bulb with a new one, still no light replaced the new one with an old bulb I had laying about and BINGO, turns out I had picked the only duff bulb in a box of ten, how's yer luck.

[Xenon]

Do you think the fact that the rear heated window, and the wiper not working could be the result of the same thing? 
 

[Xenon]

***UPDATE****
 

The problems still remains with the Audi. 
The garage have told us that they have taken the car apart again to check all the connections that they did when they replaced the heater Matrix. 

They have checked all the wiring and say they can’t find a fault.

They said they had asked several Audi specialists that can’t find what it is, one who of which who they believe to be a expert said he believed everything pointed to the Body Control Module, and that replacing this and re-coding it would hopefully solve the issue. It hasn’t.

We still do not have a solution to this issue. As it stands two of the rear lights are out ( the ones on the boot lid that line up next to the rear lights) - the reverse lights, the rear wiper and heater. 
The boot release works, as does the number plate light and the brake light at the top of the boot. - The reversing sensors also do not work.

This is the third consecutive weekend they’ve had the car with no fix.

They have told us that they have heard of similar problems where lights have stopped working when the car has gone in for bodywork repairs - meaning that it could be spontaneous and unrelated. 
Whilst that could be true, it doesn’t mean our situation wasn’t caused somehow when they changed the heater Matrix. 
If they don’t know what caused the fault, the doesn’t mean they didn’t cause it as they don’t know the cause.

 

[Xenon]

Update with the car. 
Recap.

Car brought in for heater Matrix repair

upon collection, warning light on. Rear boot lights, reverse lights, rear wiper and heated windscreen all not working.

garage rechecked twice the heater matrix connections and fuses.

hired automotive electrician who determined after his checks that it was probably the Body Control Module.

New BCM replaced and reprogrammed. Problem still remained.

Garage then noticed cable harness had slight wear in the wiring harness, where they go from the boot hinge into the body of the car.

Said they would do a bypass from the cables at the back to BCM to see if the lights would work directly, indicating a fault with the wiring somewhere in the car.

Later received an e-mail to say a rodent had chewed through the wiring having gained access through the bumper air flow vent in the back of the car (see pics)

They repaired the cables and it worked again. 
Paid a lot of money and time trying to get this sorted. 
 

would have thought the garage would have bypassed the lights quicker to determine a circuit, and that the automotive electrician they hired would have checked that before determining it was the BCM.

Wasn’t kept informed of the costs before they proceeded with further checks, just hit with a bill. 
 

Told rodent could have got in at any time, said coincidence that car was fine till it came in for heater repair change and problem noticed upon collection. No evidence of rodent faeces or nesting so it can’t have been in their long.

 

 

[Magnet]

Many thanks for the update. 
I did mention the possibility of harness damaged twixt body and tailgate - which they eventually found. 
Rodent damage:-

Probably mice, possibly living at the repair garage-? We are living in a rural area, and a near neighbour has had some wiring and diesel pipe damaged by mice. Apologies to those who are sensitive about these things ( you can pick up Xenon’s bill) but I keep bait boxes near to the drive. They will still probably prefer the comfort of a vehicle rather than the bait.
Not many love rats, and mice are thought to be nice and cuddly. Mice are incontinent, rats aren’t. 
Glad it’s eventually sorted, and thanks for keeping us updated.
Kind regards,

Gareth. 

[Xenon]

Suggested mice at the garage being the cause. Obviously they were keen to distance themselves from that idea and said they don’t have any rodent problem there. 

[Magnet]

You seldom come across folks who admit to having rodent infestation. 

[Magnet]

‘No rodent problem there’    then.
So the explanation is that you took your own mouse on a holiday to the garage and he was happy enough not chewing your wires when the car was at your home. He gets bored with his existence at the garage and really misses your home, so in his boredom, he decides to have his own back and chews your wiring. 
How’s that for a plausible explanation!? 
Kind regards,

Gareth.