The electric motor has an overload protection device connected between the red lead and one of the commutator brushes:
The motor current passes through this device which has a bimetallic strip that heats up when the current reaches 10amps and snaps to open two contacts and so disconnects the motor. This happens each time the motor hits the end stop when it opens and closes the hood cover. By the time the device cools down and the contacts close, the ECU has disconnected the supply. This technique is also used in window motors to sense the end of travel.
As the device ages however, these contacts oxidise and deteriorate until they often don't make electrical contact even though they may be touching, just like a dodgy relay, and this is why you sometimes get that silence when the hood should be opening.
Good news is that this device is made here in the UK by Otter Controls of South Buxton Derbyshire (Home page
) and is known as a "Q-Series Motor Protection Switch".
If you replace this, it will need some careful soldering as the original has spot welded connections. I dismantled mine and cleaned the contacts - be careful as they are silver and should be treated very gently with very fine abrasive and a contact cleaning spray.
After dismantling the motor, don't forget to add a small pre-load to the worm drive motor shaft as it reduces the shock loading on the nylon gear wheel:
The motor has a locknut and allen screw at the end of the shaft, and when produced at the factory is adjusted to have a certain amount of compression on the shaft.
1. Loosen the locknut (10mm spanner)
2. Tighten the allen screw until it makes contact with the shaft and then turn a further 90 degrees and then tighten the locknut. The motor should run smoothly and quickly but not show any signs of labouring.
Also adjust the cables as below:
At the motor end there are two locking nuts on each actuating cable. Loosen these and adjust the cables so that each catch is 1mm from the stop bar when in the closed position - see the photo. The cables should then both have a small amount of slack when the hood is closed.