I've recently bought a nice 1.4 TDI SE. What an excellent wee car – I'm really enjoying it.

I got the car for a decent price, partly because I knew of a potential front assist sensor issue. Lo and behold – the Front Assist: sensor impaired warning appears on most journeys, typically five to 15 minutes into setting off.

I've cleaned out a bit of loose detritus from behind the grille and lightly wiped down the front of the sensor. Unfortunately, this hasn't resolved it.

I've read a few threads on this issue, but I'm yet to see a step-by-step guide on the best way to troubleshoot this issue. What steps would you recommend a competent home mechanic take to resolve this? A few notes and questions:

• Eyeballing it, the face of the sensor doesn't appear to sit perpendicular to the road surface. This may well be by design – I only mention it because I saw someone reference this in another thread

• The top lift leg of the mount wiggles back and forth easily. Is this normal? Someone else mentioned this exact issue in another thread so, again, this may be by design

• On that note, any pictures of a working setup would be appreciated so I can compare it to mine

• This sounds daft, but how clean does the sensor need to be? Do I need to treat it to a gentle bubble bath, or is a light wipe sufficient?

• I'm a little out of my depth here, but would a code reader reveal anything meaningful about what's going wrong? I may be a competent home mechanic but this is my first truly modern car!

The car has been well looked after and came with extensive service history. I have no reason to believe it's been involved in an accident. I expect the sensor just needs to be recalibrated, but I'd like to establish that with as much confidence as I can before committing cash and time to the issue.

Should repair or replacement be required, recommendations for specialists around Bristol would be warmly welcomed.

Cheers!

Edited 15 March, 20251 yr by Jacque_Lucque

Hello JL, welcome to the forum.

There should not be any movement in the radar sensor, check that the mounts haven't been damaged or broken.

Hopefully the sensor will be undamaged if it's just been displaced in a parking bump.

Radar will almost certainly require recalibration if the mounts are replaced.

2 minutes ago, Warrior193 said:

Hello JL, welcome to the forum.

There should not be any movement in the radar sensor, check that the mounts haven't been damaged or broken.

Hopefully the sensor will be undamaged if it's just been displaced in a parking bump.

Radar will almost certainly require recalibration if the mounts are replaced.

Thank you for such a prompt reply! I will get a video of the mount in the morning and share it here.

I've had a good look at the mount in the cold light of day. The top left plastic pin/mount is sitting behind the metal mounting bracket.

Comparing this to images of mounts on eBay, it appears this is broken, or has been pushed behind the bracket.

Likewise, the right-hand mounts on the bracket of my car look as per the eBay image.

Otherwise, the mount and radar system look fine to my untrained eye.

Maybe I'm talking absolute nonsense but given there's no visible front-end damage, does this and the deformed radiator fins suggest an over-vigorous jetwash?

I will remove the grille and see if I can re-fit the mount. If not, hopefully, a replacement mount and recalibration will solve the issue.

Any further thoughts?

I'm sure I can work it out, but tips, tricks and guidance on how to remove the vent grille would be welcomed!

Edited 16 March, 20251 yr by Jacque_Lucque

It does appear that your mount is broken, most likely that the grill has been nudged in a parking manoeuvre, deflecting it sufficiently to push the sensor back. I would think it's possible to confirm the radar sensor functionality with VCDS, but certainly worth replacing the mount and getting the calibration checked.

1 hour ago, Warrior193 said:

It does appear that your mount is broken, most likely that the grill has been nudged in a parking manoeuvre, deflecting it sufficiently to push the sensor back. I would think it's possible to confirm the radar sensor functionality with VCDS, but certainly worth replacing the mount and getting the calibration checked.

I suspect you're right. Looking behind the lower vent grill – which itself is a little damaged – a section of EPS foam is missing. No matter, none of it looks especially serious.

I've removed the sensor and someone has already tried to fix this issue by stuffing a rubber anti-slip mat behind the unit to push it forward. High-tech calibration!

I tried twisting the clip into the right orientation but unfortunately – and perhaps unsurprisingly – that didn't solve the problem. I'll wait until the new mounting bracket comes and have the unit recalibrated.

If you inspect the front bumper and grille area more you might find more signs, or you might not, obviously you want the sensor fitted with everything in as much alignment as required before calibration as the system acts like a nervous passenger at the best of working, only this passenger doesn't just scream it can jump on the brake (I forget if it pulls the steering wheel too, I've no idea if it ties into lane "assist" either if that fitted to the car.

My wife's 2015 (without lane "assist", thankfully to me) throws up alarm in some normal driving conditions, I don't think I've got it as far as braking but my wife told me once it put up a message it was inactive but when she started the car for return journey the doom had gone and another time whilst she was driving slowly in town sudden braking for no apparent reason, very light traffic in distance, then she noticed an empty bag blowing down the road, whether it was that who knows.

So don't worry if after fixing and calibration you get the odd unnecessary false alarm from the front "assist".

It'd be very useful and informative if you can let us know how you get on and what's actually needed for the repair and recalibration, there are video and info about but they can be general and you never know how accurate the info is or relates to your particular circumstances and model and year.

Good luck.

Edited 16 March, 20251 yr by nta16

29 minutes ago, nta16 said:

If you inspect the front bumper and grille area more you might find more signs, or you might not, obviously you want the sensor fitted with everything in as much alignment as required before calibration as the system acts like a nervous passenger at the best of working, only this passenger doesn't just scream it can jump on the brake (I forget if it pulls the steering wheel too, I've no idea if it ties into lane "assist" either if that fitted to the car.

My wife's 2015 (without lane "assist", thankfully to me) throws up alarm in some normal driving conditions, I don't think I've got it as far as braking but my wife told me once it put up a message it was inactive but when she started the car for return journey the doom had gone and another time whilst she was driving slowly in town sudden braking for no apparent reason, very light traffic in distance, then she noticed an empty bag blowing down the road, whether it was that who knows.

So don't worry if after fixing and calibration you get the odd unnecessary false alarm from the front "assist".

It'd be very useful and informative if you can let us know how you get on and what's actually needed for the repair and recalibration, there are video and info about but they can be general and you never know how accurate the info is or relates to your particular circumstances and model and year.

Good luck.

The front radar doesn't affect the steering - just the proximity warning and, eventually, the full ABS avoidance braking. If fitted, lane assist steering intervention is monitored by the front (A5 ?) camera.

1 hour ago, Jacque_Lucque said:

I suspect you're right. Looking behind the lower vent grill – which itself is a little damaged – a section of EPS foam is missing. No matter, none of it looks especially serious.

I've removed the sensor and someone has already tried to fix this issue by stuffing a rubber anti-slip mat behind the unit to push it forward. High-tech calibration!

I tried twisting the clip into the right orientation but unfortunately – and perhaps unsurprisingly – that didn't solve the problem. I'll wait until the new mounting bracket comes and have the unit recalibrated.

Is the sensor wiring ok? in the second image you have attached, it looks a little odd.

7 minutes ago, Warrior193 said:

Is the sensor wiring ok? in the second image you have attached, it looks a little odd.

I think it looks odd because I've pulled the sensor out of the body and didn't undo the guide clip to the righthand side of the sensor, so the cable is pulled taut. I couldn't see any exposed core or wiring, so hopefully it's all fine!

46 minutes ago, nta16 said:

If you inspect the front bumper and grille area more you might find more signs, or you might not, obviously you want the sensor fitted with everything in as much alignment as required before calibration as the system acts like a nervous passenger at the best of working, only this passenger doesn't just scream it can jump on the brake (I forget if it pulls the steering wheel too, I've no idea if it ties into lane "assist" either if that fitted to the car.

My wife's 2015 (without lane "assist", thankfully to me) throws up alarm in some normal driving conditions, I don't think I've got it as far as braking but my wife told me once it put up a message it was inactive but when she started the car for return journey the doom had gone and another time whilst she was driving slowly in town sudden braking for no apparent reason, very light traffic in distance, then she noticed an empty bag blowing down the road, whether it was that who knows.

So don't worry if after fixing and calibration you get the odd unnecessary false alarm from the front "assist".

It'd be very useful and informative if you can let us know how you get on and what's actually needed for the repair and recalibration, there are video and info about but they can be general and you never know how accurate the info is or relates to your particular circumstances and model and year.

Good luck.

I will definitely report back on how I get on.

I also have my doubts about the efficacy of these systems but I'd rather not have to disable the system every time I start the car.

Though reports conflict, it's not beyond the realms of possibility that a mechanic could fail the car's MOT because a critical safety warning is present. I'm inclined to believe someone wouldn't, but that's a stress I'd like to avoid if possible!

I'm pretty sure that the front assist being unavailable is not a MOT critical failure - as it can be deactivated by the driver.

Apart from a few occasions where mine has thrown a brief warning where there was no real risk of a collision - usually when I was overtaking a vehicle that was turning-off to the left in front of me - I've found the system pretty reliable.

47 minutes ago, Warrior193 said:

The front radar doesn't affect the steering - just the proximity warning and, eventually, the full ABS avoidance braking. If fitted, lane assist steering intervention is monitored by the front (A5 ?) camera.

Thanks I wasn't sure if the systems interacted indirectly as all are about removing as much from the driver as possible for the days of "driverless" cars. I think if this every comes it will be in limited applications and areas but to many the car is already just an infotainment system on wheels and possibly also going on to a portable battery storage power system.

On the cars I've driven with lane "assist" it can be very intermittent in its accuracy of use but you are warned about this in the pages telling you what it can't do or be trusted with. I've tested the one on my neighbour's car a number of times (with him as passenger) and had something like a leaf blowing on a hedge 15 foot back from road verge frighten the poor thing which might explain it later taking revenge when I was proving the centre white lines aren't always recognised when the conditions are good as it requires and it's reaction was slow when required. This car had front, sides and rear cameras, these along with exterior lights, windows, mirrors and reflective number plates I clean as required before driving the vehicle and I was of course exaggerating (a bit) how nervous the system is, and of course at no point did I put anyone or thing at danger (there's always risk) and my neighbour used to be an amateur rally navigator in the 1960s so his only real concern being a Yorkshire man was mpg, On another occasion I proved to him following the car's gear selection/change suggestions doesn't, always at least, give best fuel economy, well yet anyway.

These systems can be very reliable, within their limitations, so very reliable in that sense, but they should not be fully relied on as a driver, they do offer assistance on many occasions but not always.

54 minutes ago, Jacque_Lucque said:

I also have my doubts about the efficacy of these systems but I'd rather not have to disable the system every time I start the car.

Things might be different if you also have this active cruise control, I don't know but IIRC (always a doubt with that) you don't have to, you can deactivate it with the car's menu, in my mind you can untick the box. Consult the appropriate manual or play with the CAR(? )menu.

A note that may or may not be fully correct but has been pointed out before, insurance, the car was manufactured with the system and insured as such unless otherwise stated so if you have a slippery and/or incompetent company/person. agency dealing with the insurance and/or any claim they say why was it off - and/or why were we not informed it was off. I've no idea if this is correct in any measure at all as we pay more for hopefully better insurance and companies dealing with them.

I got phone calls this week from, the now previous, insurer about my wife's car being claimed to be in an accident it wasn't and after talking it seemed most likely to be a simple mistake of wrong registration plate number from the claiming insurance, apparently this large well-known insurance company claiming is also known for such errors. To me it said something about the claiming insurance company's systems and staff training and perhaps management and company attitudes - but this is England so to be expected I've found from decides of experience with some insurance companies and living in England and dealing with English managements and companies over my many decades.

As for the MoT tester having a light on when t shouldn't be may not be even an advisory but it may make them think what else might be wrong and/or less tolerant about other minor to major matters, the warning isn't something that must show.

You sound like the sort of chap who will get things sorted with this, good luck.