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PDAS engaded ?

Old 12-28-2018, 12:16 PM
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Default PDAS engaded ?


Had been to the track today with my 1991 C4.

During one of the turns I heard an alarm beep,

The following 4 lamps turned on:

1. Alarm (exclamation mark).

2. ABS.

3. What I believe is the red differential lamp in the cluster.

4. The green dot for the differential in the switch console.

The above lamps would turn off only after turning off the vehicle.

Any help ?


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Old 12-28-2018, 04:07 PM
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Alternator? You get a slew of lights on the 993 when it has an issue. Cars are very similar other than your more complex differentials.
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Old 12-28-2018, 05:59 PM
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You aren't supposed to be getting alarms like that on the track.

It doesn't initially sound like a coil issue. This typically causes many lights to go on along w the alarm.

Yours seems to be just pdas alarms, which actually should signify an issue.

I'm guessing- but what i would assume is happening is that you were running out of pressure in the system. Aka, emptying the accumulator and pressure running low, and then the pump not being able to catch up before the alarms went off. Then when you turn off the car and restart, since you have enough pressure, all seems fine.

So- I'm thinking you have an accumulator that may need to be replaced or you have a leak somewhere - maybe diff seals, maybe not, or your pressure switch isn't turning on quickly enough (unlikely) , or you have air in the system after having run the car hard on the track and all is well, but needs a bleed.

Start by doing the following- car off, pump the brake pedal til it's dead hard. Then turn the key on and start a stop watch and time the pressurization of the accumulator. You will hear the pump turn on and stop the watch when it turns off. Should be around 1 minute.

If it runs significantly longer than one minute, then the accumulator needs to be replaced.

Then. If that is all good. With the key on, pump the brake pedal medium hard. Every three or four hard brake pumps should cause the pressure pump to turn on. This should be consistent. If it flips the pump on consistently, you are good there and the switch is working.

Next up. Bleed the entire system. And then after the bleed- go drive and try to replicate the warning lights.

If the wanting lights come back on- come back here and give some new evidence so it can help to determine more clearly where to look.

All that to say- your issue isn't a big one, since you seem to have brakes. But you want to run through some basics to make sure that the system pressurizes properly because if there is a pressurization issue- you will go from having brakes to literally having none - while you drive. So be careful.

The cause of your issue- just guessing- is that since the clutch , the PDAs, and the brakes all use the same system- it gets overwhelmed in a track environment- or it can.
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Old 12-28-2018, 06:33 PM
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Also check the brake fluid levels. There is a sensor that detects when the reservoir gets low and really hard cornering could possibly trigger this.
It's in the frunk drivers side. Easy to access.
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Old 12-29-2018, 06:05 AM
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I would also check brake fluid level and fill it to the max.

I track my C4 since serveral years quite often (more or less pure track car at the moment) and i have/had no issues (besides the rear drive shafts)
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Old 12-30-2018, 01:32 AM
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I had this happen a few times with my 89 C4 during very spirited mountain runs and AutoX events. I'm guessing your accelerometers may need cleaning.

Check these posts


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Old 12-31-2018, 10:02 AM
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I had a minor leak at the pressure switch... this caused similar issues when working the brake system hard. Spirited driving.

Replaced the accumulator (as it was suspect and was not too expensive). It didn't fix the issue in the long run.

Found the brake switch leak, months later when it had gotten so bad that it didn't just look grimy, but wet to the touch.
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