Right so... Recently started having a strange and seemingly very dangerous problem with my Traction Control on my 2001 S3 8L (Facelift). I first noticed the issue when cruising at about 40 mph on the way home from work last Friday evening, when upon even lightly touching my accelerator pedal, the car would start flashing the ESP light repetitively, and produce a horrific grinding noise from the driver side footwell. The noise really was horrendous, and sounded mechanical - seeing that the ESP light was flashing, my hand shot straight for the 'ESP Off' button in my centre console, and as I'd hoped, instantly the noise disappeared, and all seemed well, just obviously, no Traction Control for the time being. I drove the rest of my journey home with my ESP switched off, until I reached my road, where I switched it back on just to see if it would do the same a second time. The car behaved herself, no problems whatsoever, and so the issue was put to bed as a one-off. How stupid I was to think like this... The next day, had a few errands to run. Didn't think twice about running with the ESP switched off, and so, left it on. The car ran absolutely fine for about an hour or so, and then when coming off probably the largest roundabout in my area joining a nice string of traffic, I went to hit my brakes, and the dreaded noise and flashing ESP light returned. The more worrying part though, I had next to no braking power, the ABS Pump was kicking in like mad completely unecessarily, to the point where my brakes were barely even working. I had to slam my handbrake on to avoid going into the back of a lorry, whilst frantically reaching for the ESP button. Really was a close one. Very dangerous. I drove the car home immediately, Traction Control off of course, and rang AMD Tuning in Essex to try and get an opinion on the issue and arrange a VCDS Scan. Using my somewhat basic to intermediate knowledge of my car and how it operates, my first thoughts were that the Lateral Acceleration Sensor could be knackered. After a scan at AMD, completely FOC I might add (thanks very much guys!), the following fault was returned: YAW Rate Sensor - Implausible Signal AMD did a few more tests, driving it around their car park, trying to replicate the issue with the VCDS connected at the same time, but the issue wouldn't occur - it'd only happen without the VCDS connected. AMD suggested that, as per the fault code produced, it is most likely to be the YAW Rate Sensor at fault. For the time being, they programmed the ESP out completely via VAG.com, to ensure that I physically cannot enable ESP at all and stop the issue from rearing it's ugly head again. After doing this, we tested to ensure the ABS was working correctly, and it was perfectly. So a breakdown of my issue: If ESP is enabled, under braking or acceleration, the ESP light on the dash flashes repeatedly, and the ABS Pump kicks in, causing a horrific grinding noise from the driver side footwell. Acceleration is slowed by the fault, and braking strengths are made dangerously weak. The only fix for the issue is to disable ESP completely. I've read a few threads on here talking about the Longitudinal and Lattitudinal Acceleration sensors on the car going faulty, and causing similar issues, but none quite like mine. Furthermore, the correct locations of these sensors seem to be somewhat disputed - some say they're both on the steering column, others say one is behind the glovebox, and a few are saying that there are three sensors as opposed to two, the third being the YAW Rate sensor as described in the VCDS fault code. To replace the YAW Sensor as shown up by VCDS, I've been quoted over £450.00 ex. VAT for the part alone, which seems to me, a rediculous price, and one that I can't really afford. Some people have been saying that the Longitudinal Sensor is exactly the same as the Lattitudinal Sensor, the only difference being that it is far cheaper! Is this even true? So really my question is - how do I fix this? All I really want to know is, which sensor do I need to replace? And is there any way at all of me avoiding having to pay stupid money? Sorry for the essay, but just wanted to provide as much information as possible from the word go. Thanks in advance for your help guys!