C5 X7 auto hold failure - not handbrake failure

[ciaranwebb0]

Hi chaps,

Just posting a new thread to see if anyone has had this issue, as I'm not due to be anywhere near Lexia / Diagnostic equipment / a mechanic for a month and a half, as I am on holiday with the car.

I've seen loads of threads online about ESP / Auto Handbrake Failure / Anti-Rollback failure but I seem to only have an intermittent anti-roll back failure (i.e. no auto hill hold), which disables the auto handbrake function as a consequence. It's bizarre because the handbrake still functions manually exactly as it is supposed to, and I don't have any ESP / anti lock braking troubles. Just FYI, it's the electronic parking brake setup. I've tested a hard brake and the anti lock still works.

This error seems to come and go - it seems to occur when in standstill traffic and I assume the engine bay is hot. It happens a little less often when the AC is on and my working theory is the two radiator fans keep everything fairly cool.

Appreciate a diagnostic is near impossible without Lexia and I will get it done as soon as possible, but just wondering if anyone else has seen this failure mode before? My assumption is that it is maybe a marginal fuse or fuse box, potentially something to do with the ABS? I would have expected an ESP error if the latter was true.

Cheers, Ciaran

[GiveMeABreak]

Hi Ciaran

The whole system is controlled by the ESP ECU. There is a handbrake ECU, but that is the slave and is controlled by the main ESP ECU. When there is an issue, some features are disabled for safety reasons. In the case of the C5 X7, the hill start assist function is provided by the Electronic Handbrake acting on the callipers, unlike later systems, where the ESP system uses the brakes directly to maintain hill braking for a few seconds.

For minor issues, you'll still have braking function, but the automatic mode and Hill Start Assist may not function. So just be aware to apply the brake manually and try not to park on a hill just in case!

[ciaranwebb0]

Thanks Marc - okay, sounds like it should limp on! Am hoping it's not the handbrake unit itself, that sounds expensive. Uphill reverse parallel parking is *interesting* with the random delay introduced by an electric handbrake

Have a great evening,
Ciaran

[GiveMeABreak]

No worries, fingers crossed, have a great holiday.