Found on cars built between 2003 and 2009, the electronic handbrake unit has become a common failure at around 80,000 miles. Failure time depends on journey type and frequency of application.
The least number of miles we have seen at failure was 35,000, and few seem to pass 120k before needing work.
Removal is detailed in the video on the right
Once you remove it you can send it to us for repair.
There are 3 common faults.
1) Worn out motor.
Inside the unit, there is a small motor, operating a gearbox, in turn operating a screw thread. Wear on the motor brushes is common, resulting in a dead short through the motor.
The photo to the right shows a new, old and dead motor. Note the brushes on the dead motor have completely worn away, and the copper springs holding the brushes have contacted the armature, and worn away.
This fault will typically show ‘ internal motor error’
2) Relay failure
When the motor shorts out, it draws large currents through the relay mounted on the circuit board. The large current causes the relay to overheat, and become unreliable. Sometimes the heat is so intense it causes the plastic covering to blister, as shown in the photo to the right.
A blistered relay is a definite reason to change the relay, though the lack of a blister does not always mean the relay is good.
3) Seized cable
In particular with the Grand scenic the left hand side cable passes over the exhaust on the way to the brakes. The heat from the exhaust seems to cause the lubricant to dry out, and the cable to seize.
When the unit is removed, it should be easily possible to move the cables by hand. The inability to do this easily is indicative of a poor cable.
The following photographs are taken from the refurbishment and repair of a Grand Scenic.
This is how it can arrive at our workshop, though removing the box’s cradle saves postage for both of us.
Here we are removing the caps for the cables – we will need these later on, so gently does it……
And then with the top removed.
The next stage is to remove the cables, motor gearbox and circuit board, so the 3 big cables need to be cut off.
In this particular case the screw thread had over tightened, and the thread had jammed – so we’ve cut the left hand cable off with a grinder to assist in the disassembly process. These cables were seized anyway, so no big loss.
The emergency release gland was in very poor condition so was replaced
Once the motor is out, the thread can be sorted out – it’s clamped in the vice here – it’s a left hand thread, so counterclockwise to tighten.
The thread must be salvaged for further use.
This is what the new motor and renovated gearbox looks like – we have used the old gearbox and paired it with a new motor.
You can see the brass thread in the gearbox – this is the thread from the old box.
Now the emergency release can be removed, and the casing cleaned internally.
Now the reassembly starts, first of all with the emergency release getting a once over, and a reseal.
After this the new motor / gearbox unit goes back in.
This pic. shows the motor and the emergency release all back in.
The new cable has been assembled, and the force sensor
(the unit with the bar code in the centre of the picture) in position.
The emergency release needs to be tested at this point…Just in case.
Now for work on the circuit board.
Gently removing the relay, and cleaning out the holes.
Occasionally we see damage to the board and the holes. We can often repair these as required. We will do almost everything we can to keep the board to prevent the loss of data – it assists in the automatic function of the unit for example and means you don’t have to code it back to the car using specialist software.
Once this is done, and the new relay soldered back into position, the circuit board can be mounted back in the box. We usually make temporary connections to the motor at this stage and test the unit.
This can be a simple job taking a few minutes, or a long and drawn out mammoth session, depending on how difficult it is to clear them. Occasionally there will be issues with the car that need addressing – but in this case, it’s on our test car which we know is good.
So then it’s soldering the wires up, and resealing the unit.