Hill start assist won't release

[Oliver350MWB]

Hi

Having a real problem with the hill start assist on my van (2009 2.4 rwd mwb High top).

The problem is when it activates it just won't release. If im not blocking traffic i have waited several minutes for it to let go and when it does it very slowly releases the brake pressure, the brakes are creaking like when you hold the brake on an auto while in drive. Nine times out of 10 I am blocking traffic and have found a quick cycle of the keys is an instant fix.

The green light on the dash goes off like it should when I pull the handbrake or push the clutch but If I try to drive off it starts burning the clutch.

So far I have recallibrated the longitude sensor and steering angle sensor, and did a self test of the abs. No faults found and this had no effect.

Clutch switch and brake switch are working (showing on and off) checked with forscan.

I've tried the three pedal push to disable and that did nothing. No light flashed on the cluster.

Tried coding it out by telling the van it didn't have hill start assist via forscan but that didn't stop it coming on.

There doesn't appear to be any water ingress in or near the bcm. Can get the cage off the pcm to have a proper look.

There are faults showing on the van but there boost faults and something to do with ' battery sounder', nothing that should effect the hill start, if anything I would have thought that a fault would disable the system not let it stick on.

Anything else I can check, i haven't ruled out a sticking caliper yet but I have touch the wheels after a drive and there was no noticeable hotter wheel.

Anywhere else I should be looking. I would like it working. As avoiding hills when all around me is hills is not fun.

Thanks

[fortyeight]

sticking caliper piston or handbrake adjusted too much

[Jim Archer]

I'm not sure a sticking piston or handbrake would be enough to stop the vehicle moving, sounds more like a sticking release valve in the ABS unit - or a sensor problem stopping the valve coming off.

Does the brake pedal go hard when it's stuck on?

Jim

[Oliver350MWB]

Hi Jim.

No the pedal doesn't go hard unless I pump it. I've just been out checking the livedata and when i press the pedal it registers the pressure being applied and releases all the pressure when i take my foot off the pedal but if i activate the hill assist the brake pressure being applied sticks at around 10-14 kpa, turning the key off now does nothing, neither does pulling the hand brake or selecting an opposite gear.

What are your thoughts?

[Jim Archer]

The pedal going firm is part of the normal Assist regime - the ABS module gives feedback to the pedal by firming up the feel.

What happens if you select reverse when facing uphill? It should release pretty much instantly.

Jim

[Oliver350MWB]

No mate. The normal ways to switch it off do not get the brakes to release any quicker.

From reading the live data The brakes do not stick on at all during normal braking. I take it this would rule out calipers or flexi lines being at fault?.

the brakes are only sticking or to be correct very slow to release once the HSA has activated.

[Jim Archer]

If key/power off releases the valve, I reckon you have a sticking relay in the ABS/Hill assist controller module. Be worth checking the plugs/connectors for it and the ABS pump for water or corrosion.

Jim

[Oliver350MWB]

Hi, the abs pump looks very scabby so rust is a good shout. Couldnt get the water bottle off today to check out the plug, not enough light after work.

Any ideas which relay controls the abs / hill start assist.

[Jim Archer]

Sorry, not idea what will be doing the Hill Assist bit.

I'm fairly sure - but don't quote me - that the ABS pump itself is likely OK if power off resets the Assist. Though it is possible the solenoid is shorting and that makes it latch - I would expect that to show a code though as it would be staying energised when the ABS controller unit thinks it should not be.

My money would be on the relay that energises the Hill Assist staying latched - for whatever reason.

Jim