01coccobet

Hi all,

I've done a little search with no luck...

My problem with the brake booster started few days ago,when I turned the car on,I got stiff pedal + brake pressure red light on(no sound from the Hyd pump).sounded strange.

I started to search for the fuse then for the relay,but unlukly the diagram in the front hood is only for the upper part f the realys,not for the relays that sit in the bottom of the front right side(when seated)

Now after few try with connection spray,cleaning,removing-reinstalling etc,it's working fine,but I could feel the relay # 68 quite hot(should be the ABS-one)but is the one that,if moved,mede the pump starts again.

the brake booster relay should be the 66,and is black instead of green.

Does anyone coud help me,or at least could give me an electric wiring diagram(couldn't find anywhere)

If I made mistakes,don't be too hard on me and just say

cheers

01coccobet

I forgot to say that Streather states at page 390:
fuse 46 ABS checked ok
fuse 47 hyd brake boost pump & DME ECU checked ok
R65 ABS motor driven pump checked ok
R66 hyd boost pump (the balck-one) don't know
R68 ABS valves checked very hot,I exchanged with the R65(are the same),but didn't have a chance to feel if it got hot again.....

ciao

01coccobet

any idea?

e9stibi

You have PM

01coccobet

A public thanks to e9stibi,really great effort to help-me.

No luck yet....

Just to let you know

I checked for line leaking,changed ralays,checked brake fluid level ecc,no luck

Cheers

01coccobet

yesterday I Made sole new checks,and found that if I kinda move the electric-pump assembly(front hood unger the front black plastic cover)it starts randomly....looks like an electric issue or maybe a stuck mechanism...

anyone had this issue?does exist a low level fluid sensor that switches off thebbrake booster pump(even if my fluid level looks ok)?
cheers

01coccobet

anybody there???

k722070

maybe try the 993tt forum for a more concentrated search of the C4 brake booster system?

Mike J

This is not a common area to fix, so that is they there are not that many responses. You might get more in the Turbo forum, since all the Turbo's have this system. Again, they have more issues with the clutch circuit than the brake circuits....

If you wiggle the unit, and it starts, then is sure sounds like a bad connector or broken wire. I do not know if there is any mechanism to shut off the unit if the fluid is low. There is a brake level sensor in the reservoir, but I think that only drives an indicator bulb on the dash.

Can you isolate the issue so just by moving a particular wiring harness so it starts/stops?

If you have access to a Bosch Hammer or PST2, you can perhaps cycle the pump and see if that give you any indications of what is wrong.

Your first post indicated that it seemed to be fixed - but then you said was was not. Is it totally not working, or erratic?

Cheers,

Mike

01coccobet

thanks guys,
I'll get the turbo way!!

Yes it's erratic....

at the beginning I just moved the relays in the front hood and started,so that's way I tried to chanfge them...
than didn't work,the other day I opened the black part to have a deeper check,and moving the top part worked......so,following this path,the problem will be surely in the trunk!!!!

ah ah ah

cheers

kjr914

As Mike above suggests, if you move electrical stuff around and it starts to work, that's generally the electrical contacts. Pull things apart, lightly sand the contact surfaces with emery cloth, or I've just scratched at the contacts with a screwdriver in desperate situations, and use electrical contact cleaner (formerly known as TV tuner cleaner...back when TVs had *****). Sometimes, even unplugging, plugging, unplugging, plugging, the connection repeatedly will knock the oxidation off and make things work again.

Is the relay still getting hot?

Garth S

If a relay becomes hot in operation - and the fuse for that circuit remains good, it is generally poor contacts on the power circuit internal to the relay ( #30 to #87/87a/87b) ..... or the solenoid that pulls these contacts together ( trigger circuit #85 to #86) is weak, the latter due to corrosion in the smaller diameter leads or female contacts for the spade terminals of the relay.

Quick check is to pull the relay, and (temporarily) insert a fused jumper wire between the relay slots for pins 30 and 87 .... or, insert a fresh relay .... or pull the cover off the relay and examine the contacts

Chemical cleaning of the relay panel contacts may be advised Deoxit/stabilit/etc .... or the Italian equivalent

Note that that area is very prone to sulfuric acid corrosion .... fumes from an aging battery or a leaking battery case ....

Once running, it may be a good idea to purge fresh brake fluid through the ABS/Booster Pump/spherical accumulator.
If not executed previously, the abbreviated procedure is to turn key on until the pump stops running: disconnect the pump wire harness, and then turn the key off. Connect a hose TIGHTLY to the bleeder valve on the spherical accumulator .... and very carefully, bleed/release the pressure into a container [ this is a high pressure release - protect your eyes] ..... at that point, a C4(S) can be bled at the calipetrs if desired like a regular car.

01coccobet

Few days around europe stopped me to follow you....

Yes the relay 68 becomes hot,but it's the abs-one,not the brake booster,so shouldn't be this the problem...or at least,it's another problem(hope not).

I tried to change all 3 relays related to the brakes(# 65;66;68),but didn't change the 60 ams fuse(I think they work cause it's an intermittent problem),but still no luck!!!

cheers again

01coccobet

after few voltmeter test in the relays bay relays 68 66 65(87-30 pin bridge showed 12 volts)

I tried hte voltage in the booster pump electric motor and I didn't get any voltage with ignition on or off.

here is the pic

01coccobet

Attachment 576401