[Resolved] Brake Fluid Level Low / PSM Failure

[dlipka]

Hi,

I have an intermittent problem with my 2001 TT.

On a track day today, I experienced the following problem after cornering hard for the first time - the dash display lit up with the following warnings all at once:

- Brake fluid level low (it isn't);

- PSM failure;

- ABS failure;

- Brake modulation failure.

I continued the 20 minute session and during this session it was clear that PSM and ABS were not working. On shutting the car down and restarting the messages and warning lights disappeared.

During the next two sessions, exactly the same thing happened.

On the fourth session, no warnings presented and both PSM and ABS worked for the whole session.

Driving home there were no issues.

There appear to be no recorded fault codes.

Any suggestions would be greatly appreciated!

Thanks,

Derek

[Loren]

When was the last time the brake fluid was changed and bled?

Not an uncommon problem if moisture is brake fluid.

[dlipka]

Hi Loren,

Fluid is about 12 months old and was last bled about 6 months ago. How does the system know that there is mositure there?

Having said that, I am unsure that they are bleed properly - I can't get the Durametric system to run the booster pump, so all bleeding is done the conventional way... Any suggestions?

Thanks,

Derek

[Loren]

What happens is that if there is moisture in the system and brakes get hot then the water turns to steam and the compressibility changes - sometimes drastically.

What kind of brake fluid now and before? If they are vastly different (like conventional to synthetic) you may need to do two flushes to get all the old out.

If it were my car I would replace the brake fluid and do a full system bleed.

[dlipka]

Thanks Loren,

Dot 4 before and Dot 4 now (conventional fluid both times). And the pedal feels good.

Also, the warnings came up right at the beginning of the session - no heat in the brakes.

Having said that, I wonder whether it isn't trapped air in the auxilliary pump circuit - what is the best way to bleed this?

Regards,

Derek

[Loren]

You will need Durametric software, or a PST2, or a PIWIS to manually run the ABS pump.

[dlipka]

Thanks Loren,

I had a play around with the car and the Durametric system on the weekend (even down loaded the latest version).

I can get the PMS / ABS / Brake Distribution to occur consistently by hard cornering - even when the car and brakes are cold.

Occasionally this will bring up the fault code 4276 "valve supply voltage". Working through the manual this refers to the hydraulic pump in the abs unit - I have done all the other checks in the manual and they are ok. Leaving me with "replace hydraulic unit". I still feel that a brake bleed might fix the problem, but my software will not run pump....

Suggestions?

Thanks,

Derek

[puma]

i know i had a weird code when i put too much oil in the canister, check to see if you are above the max line.

[DasBoost]

you can run the pump alone using a +12v jumper wire, then bleed with motive while pump is running. Will not of course cycle the valves tho.

[dlipka]

Thanks for the feedback - when you say too much oil in the canister, what do you mean?

The ABS unit is wired up through a large plug - how do you use jumper wires to run the pump? (the fault is coming up as the 'hydraulic unit' (abs pump), not the pump under the master cylinder which is called the 'pre-charge pump'....

[dlipka]

I have solved the problem - and really only by chance. My everyday car is a Holden Monaro (Pontiac GTO in the States) and while I was fixing my trailer lights the other day, the battery ran down - when I went to start the car, the battery was too low and the solenoid would not kick in (it just clicked). At the same time the car told me I had an ABS and traction control failure. This got me thinking...

I already had the Porsche up on stands (replacing the disks & pads as well as doing a few other things) and when I reconnected the battery, it was stone dead and wouldn't subsequently charge. Replacing the battery has appears to have solved the ABS / PSM problem - everything works now.

My theory is that the problem was created by a failing battery - as the car cornered hard, the voltage on the failing cell dropped, dropping the overall voltage below the threshold required by the ABS unit, hence causing it to 'fail' / post the warning messages.

I am not sure whether the fact that the voltage dropped so much, points to a failing alternator or not. Thoughts?

Loren, could you maybe edit the heading of this post to indicate that the problem has been solved?

Thanks,

Derek

[wross996TT]

Porsche cars are very sensitive to battery issues. Quite possible you will get (what appears to be) random codes as a result of a failed battery. Glad you got it sorted.