ABS Unit under bonnet

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Les Constant
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Location: Swanscombe, Dartford, Kent
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My G is 300 GEL 1993 and it is experiencing a problem with the ABS unit.

Every now and then the ABS unit emits a whirring noise like as if a small fan is running this continues for a while after the engine is switched off and normally stops whirring after a short while however this time the noise coming from the ABS unit is continuous and only stops when i disconnect the battery, please can any member advise on how I can remedy this issue.    

Regards from Les

JASONGDS
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Re: ABS Unit under bonnet

Never had that, does Abs light function normally? Earth straps etc all good? How old is brake fluid? Presume this unit same as of era so a M B indepedent might be able to help

Pistonhead
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Re: ABS Unit under bonnet

Just to be clear, does the noise continuously sound regardless of brake application or not? If concinnous, I have never come across that one. It sounds that the ABS internal motor bearings have become noisy but as I have mention this has been unheard of. I'll have to look into this one.

Les Constant
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Re: ABS Unit under bonnet

Hi and Thank you for responding, The whirring noise is continuous and is coming from the ABS unit and in particular from under the small black cover plate,    it sounds as if a small fan is running under this black cover,  it is secured by one fixing screw, 

Shall remove the cover to investigate  ?

I have left the battery connected now for around 2 hours and the whirring has not stopped and the ABS unit is warm\hot to the touch.

Any other thoughts as to the reason this will not shut down.

Also the ABS light also started coming on intermittently.

The brake fluid is old i am not sure when it was last replaced.

Also i have been getting a grumberling noise and some minor shuddering from the brake pedal

Thank you from Les

PS  i have just removed the black cover, and also the silver BOSCH relay and the noise has stopped, do you think the relay could be faulty ?

JASONGDS
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Re: ABS Unit under bonnet

You could search Bosch numbers for relay, hopefully not expensive  to try one? A bit of feedback through pedal is normal for gravel etc, but not  on a smooth surface.

I would change brake fluid an easy bleed will work well. On no account leave ignition switched on during bleeding of fluId

Pistonhead
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Re: ABS Unit under bonnet

Try and wriggling the relay and see if the movement affects the noise. To change the relay is a cheaper option and brake fluid should be renewed every two years, if the reservoir is showing darken brake fluid colour as opposed to a light amber colour then definitely the brake fluid is due for renewal and another option to try out. Before looking into the ABS Motor. 

Will the ABS activate under hard braking? - Your brake pedal will pulsate as this is active. Make sure there is no traffic behind you when you attempt this, better still use a quite road to do so.