ACC and TPMS errors

[DougUK]

10 months into ownership of my '63 p/p Mk7 GTi I'm counting the cost of: light and rain sensor replacement, coolant sensor replacement, coolant pump replacement and various other niggles.  This week I've had intermittent tyre pressure warnings which I am ignoring as the pressures are all fine, but now I have front assist and ACC errors which are pushing me to limp mode.  I've cleaned the front sensor and de-activated front assist but no joy.  I've also had a couple of emergency city brakes that were phantom.  Having read up as much as I can it sounds like it isn't actually the ACC system but more likely something else.  Before I hand another £1k to the dealer, has anyone experienced this and can offer any insight?  I can live without ACC but phantom braking and limp mode do render the car somewhat useless!  TIA.

[fredgroves]

TPMS phantom triggers are usually caused by sudden temperature drops, which you can get at this time of year. Its unlikely to be a problem unless you are seeing loads a week.

Phantom front assist triggers are also pretty common too, again no fault on your kit, just weird radar reflections. Did it just ping up red on the dash or dab the brakes or fully lock up the brakes? (once it triggers it largely depends on your reaction times, because the system escalates the action automatically)

What sort of ACC error are you seeing?

[DougUK]

Thanks, Fred - it's just a dab on brakes and red centre front panel on the instrument cluster. The ACC is a warning that "ACC is not available" which then sits as a warning light.  It's the only thing I can think that is initiating limp mode.

[fredgroves]

I did have one "ACC not available" messages once (other than in heavy snow) and that didn't clear no matter what I did until I left it over night and it was gone again in the morning.

Most errors you can see bugger off if you switch off for 30 mins, but usually if that doesn't clear it, its broken somehow, which was why I started worrying... but then it was clear in the morning.

I'd be careful about the dealers though, they will be wanting to swap the unit and realign it because both of those things are beaucoup dollar for them...

[golfdave]

you need to get (or find someone who has) vcds or obd11 & do a full scan  to see what comes up as fault codes...

Some generate without triggering lights but cause background electric gremlins...& sometimes a genuine bit of nature/driving/incident causes the sensors to freak out for no apparent reason as the BCMs can't compute the data..

TPMS is all within the ABS unit...& it can take up to 1hr of driving to relearn the wheels when you press the "set" button on the screen

[DougUK]

Thanks golfdave, I ran a scan on OBD and found no fault codes.  All warnings have disappeared and ACC is unable to be set so appears to have somehow withdrawn itself although cruise control does work.  I tried to test the city brake to see if the sensor was still active, with some very late braking but couldn't get it to activate.  My conclusion at the moment is the sensor is not functioning (without logging a fault) for reasons unknown but it hasn't prompted limp mode the past 3 days so I can live with it for the time being.

[mcmaddy]

If the radar sensor was faulty you'd be getting braking errors on the dash.

[Papa John]

You could try disconnecting the battery and leaving it that way for half an hour; hopefully a hard reset on the cheap? There's also a used radar unit on eBay item number: 292309751724

[fredgroves]

Testing city braking is difficult actually because you literally have to make no driver inputs at all for some time before the detection occurs.

Its not just braking, steering or throttle will also be considered inputs.

[Papa John]

Testing city braking is difficult actually because you literally have to make no driver inputs at all for some time before the detection occurs.

Its not just braking, steering or throttle will also be considered inputs.

That's where the performance pack (R) brakes are very handy indeed. Seek out an an trustworthy idependent VW specialist? at least you won't be paying VW main stealer prices...