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Old 02-07-2010, 11:21 AM   #1
porsche965
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Default ABS and Differential Light coming on in dash

Hi,

The weather has begun to dry up here in Ireland eventually so i decided to taken my 90 C4 964 out for a drive (parked in shed for last couple of months), just last night while i was driving the car the ABS and Differential lights came on simultaniously on the dashboard with the buzzer noise also activated, upon seeing and hearing this i pulled over and turned off ignition, i left the car off for about 5 minutes and then started it again and everything was ok, however again today after maybe driving 11-15 miles the two lights came on again!

Can anyone help me out here with what might be causing this problem?

Any help or advice would be greatly appreciated, thanks in advance

Regards,

Nelius
Ireland
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Old 02-07-2010, 11:37 AM   #2
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Check the level of your brake / clutch fluid.
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Old 02-07-2010, 11:49 AM   #3
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This *could* be a serious problem, so please look carefully at your hydraulic pump circuit before driving.

I don't mean to be alarmist, but the hydraulic system is integral to braking and alarms in this circuit could be serious. Your problem could be very simple, but better safe than sorry.

In particular, check the front boot area, under the carpet and under the spare tire to determine if the pressure switch on your hydraulic pump is leaking. If so, you could end up without brakes. Rather quickly, I might add! The switch, itself, can be replaced.

If the switch is faulty and the pump runs continuously you could also overheat the pump resulting in the need for a replacement; which is very expensive. The switch is not very expensive.

Of course, it could be as simple as being a bit low on the brake/hydraulic fluid reservoir. However, a combination of both the lights and the horn is the maximum warning alarm, so you should take care to diagnose what's happening.

Here are some notes (and thread ref's) to get you started:

Code:
    - Hyrdraulic Pump Pressure Switch
      Indications
        Warning lights on
          lights on oil temp/press gauge
            ! master alarm light
            #8 4wd system light
              (upper right; 4 wheels and trans diag)
            #13 brake pressure light
              (bottom center; upper right of cluster; brake pads w/ ! in center)
        Beeper
          gong relay (?)
          this is a low pressure indicator
          STOP, TURN OFF CAR
          if pressure goes too low you can loose bakes and/or
          run the pump dry and destroy it
      Diagnostics
        Wait until system finishes pressurizing
          lights should go out in ~40 secs after starting car
          should hear pump running
          don't let it run more than a couple of minutes; will overheat
        Low fluid
          should be full up
        Fuse #15 (18?), 40amp - hydraulic pump
          check and/or replace
        Relay #51
        Ground points
          remove and clean all ground points in front trunk
        Clock cold solder joint problem
          sometimes lights go out when rev's reach 3000
          this is a charging system ciruit malfunction due to solder joints
          should have charging light on, as well
        Pressure switch seal
        Pressure switch
        Pump
      Parts
        999.707.094.40 Rubber O-Ring
        964.606.904.00 Pressure Sensor
        964.615.135.00 Relay hyd pump
        993.355.953.01 Part number
          Smith Motorworks (ebay)
          has this pump (says 993 part) for $1500
          http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&refid=store&category=42605&viewitem=&item=190000002658
      Links
        Pump Repair - dynatechcorp_com
          http://stores.ebay.com/DynaTech-Corp...QQftidZ2QQtZkm
        C2/C4 Technical Stuff
          http://www.ncweb.com/~rochford/tech.htm
      Threads
        Hydraulic Brake Pump Failure
        Stiff brake pedal - No braking!
        Methodical C4 Hydraulic Pump
        964 C4 Hydraulic pump leakage
        Problems with the high pressure hydraulic system
        The 89-94 964 C4 pump
        Total brake failure....without WARNING!!!!
        C4 PDAS/ABS Update
        Brake problem only 964?
        Warning lights on this morning
        Best source for PDAS pump and/or pressure switch?
        Assisted Breaking Failure
        PDAS & Brake warning light and Buzzer *FIXED*
        Loud buzzing from ABS unit
        ABS Problem
        ABS pump stays on
        ABS failure
        Brake failure - leak at ABS pump
        New owner / abs/4wd warning light
        PDAS/ABS warning - a solution
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The hours a Porsche spends parked. You don't get those back.

Last edited by dfinnegan; 02-07-2010 at 11:55 AM. Reason: turned the thread ref's into links
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Old 02-07-2010, 12:03 PM   #4
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One more thread: Hydralic Pressure Switch Replacement
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Old 02-08-2010, 05:21 AM   #5
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Thanks guys for your responses,

On my way home yesterday (after posting my message) to put the car back in storage, another strange thing happened, as i was entering my house all the lights in the dash board came on along with the buzzer (same as when you turn the key in ignition, with the exception of the buzzer) however the car was still runnig and did not cut out at any point, i am now begining to wonder if it is an electrical problem i am having (new battery put in car this week only). Could the altenator be acting up and causing this to happen?, i will still check my brake fluid levels tonight though.

As you can well appreciate Ireland is not a wash with Porsche dealers or Mechanics so it is hard to get problems solved over here.

Regards,
Nelius
Ireland
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Old 02-08-2010, 06:33 AM   #6
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Dear Porsche965

With all the lights lit up on the dash "it's beginning to look a lot like Christmas"

Bill
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Old 02-08-2010, 08:05 AM   #7
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Quote:
Originally Posted by darth View Post
Dear Porsche965

With all the lights lit up on the dash "it's beginning to look a lot like Christmas"

Bill
Darth,

I thought christmas only came once a year!!!!. i will have to look at the Christmas tree effect posts so to get me out of this one.

Regards,
Nelius
Ireland
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Old 02-08-2010, 09:00 AM   #8
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There are many posts regarding the Christmas Tree Effect. Many have solved the problem by replacing coils.
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Old 02-08-2010, 09:38 AM   #9
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Thanks steven

Regards,
Nelius
Ireland
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Old 02-08-2010, 10:03 AM   #10
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Start with what's recently been changed . . .

Check the ground strap from the battery to the body.
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Old 02-08-2010, 12:13 PM   #11
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Quote:
Originally Posted by dfinnegan View Post
Start with what's recently been changed . . .

Check the ground strap from the battery to the body.
Thanks dfinnegan,

Will check this when i go home from work this evening, will keep you posted on the outcome (fingers crossed its only a small problem like that)

Regards,
Nelius
Ireland
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Old 02-08-2010, 01:12 PM   #12
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Hi dfinnegan,

Do you think that the two issues above could be related, i.e the lights for the ABS and Differential coming on ocassionally since i put in the new battery (during the weekend) along with the "Christmas Tree Effect" ?

Regards,
Nelius
Ireland
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Old 02-08-2010, 01:27 PM   #13
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I wouldn't expect a relationship between hydraulic issues and the christmas tree light show.

Conversely, it seems possible that the christmas tree effect could give rise to hydraulic warnings; although I don't recall that manifestation being reported on the board before.

I had my hydraulics fail due to a leaking pressure switch and the event left a strong impression on me.

That said, these cars are very sensitive to stray voltage/current and all sorts of things can occur from poor running and missing, to stray warning lights.

One of the smart folks here once posted and asked "what's changed recently". That makes a lot of sense to me so I suggested the battery checks. Some folks have reported bad ground wires even though they measured out okay with a mulit-meter, so changing the battery seems suspect.

Still, do look at the hydraulic fluid level, look for leaks and measure the time to prime the pump on initial key ignition. It should run ~40 secs, or less after sitting for a day, or so. And the pump should turn off. I can easily hear mine, but I'm sensitive to it. Note that if the pump runs an minute, or so, it's not alarming, but does point to potential issues. That could be as simple as a fluid flush requirement.

Best of luck diagnosing. Keep the info flowing as there are lots of very knowledgeable people on this board and they are very willing to jump in and help out fellow enthusiasts.

Cheers
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Old 02-09-2010, 05:32 AM   #14
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Quote:
Originally Posted by dfinnegan View Post
I wouldn't expect a relationship between hydraulic issues and the christmas tree light show.

Conversely, it seems possible that the christmas tree effect could give rise to hydraulic warnings; although I don't recall that manifestation being reported on the board before.

I had my hydraulics fail due to a leaking pressure switch and the event left a strong impression on me.

That said, these cars are very sensitive to stray voltage/current and all sorts of things can occur from poor running and missing, to stray warning lights.

One of the smart folks here once posted and asked "what's changed recently". That makes a lot of sense to me so I suggested the battery checks. Some folks have reported bad ground wires even though they measured out okay with a mulit-meter, so changing the battery seems suspect.

Still, do look at the hydraulic fluid level, look for leaks and measure the time to prime the pump on initial key ignition. It should run ~40 secs, or less after sitting for a day, or so. And the pump should turn off. I can easily hear mine, but I'm sensitive to it. Note that if the pump runs an minute, or so, it's not alarming, but does point to potential issues. That could be as simple as a fluid flush requirement.

Best of luck diagnosing. Keep the info flowing as there are lots of very knowledgeable people on this board and they are very willing to jump in and help out fellow enthusiasts.

Cheers
Thanks dfinnegan,

i really appreciate all the help and information you have given me, its not easy to get info on Porsches over here in Ireland, so i am greatfull to you and all the Rennlisters for any words of wisdom that can be put my way.

Regads,
Nelius
Ireland
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Old 02-09-2010, 12:25 PM   #15
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I'm signing on to this.

I'm having the very same issue(s).... Mine is a C2 - not a 965 - so no hydraulic pump / pressure switch, right..?

Mine may well be a ground strap. Along with - or sometimes alone - I get a "blink" in the electrical system: The radio stops for a second (sometimes longer than a second, and I have to reset the code), and the radar detector resets...
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Old 02-09-2010, 12:25 PM
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