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Join Date: Nov 2013
Location: Torquay , UK
Posts: 77
Garage
964 C4 MacGyver PDAS fix.

Slighly long back story. From one day to next the following.
Alternator light not working, spoiler and airbag lights stay on, speedos, both dial and digital in OBC not working,PDAS and ABS light w buzzer on from start.
Clock: check bulbs, re-solder and measure - OK.
Alternator back.
Check PDAS multiplug. Some water ingress, bluegreen corosion and ,damn, one pin broken, no 9 ' ground accelerometers'.
Clean multiplug. Remove control unit. Clean pins. Removed back lid, no signs of water ingress. Bonus.
Refitted.
Speedos back, spoiler light turning off at speed. Airbag, PDAS/ABS light and buzzer still there.
Fix attempt.See pics. Cleaned broken pin 9 with mini dremel. Made small cross shaped pin fix from thin wire and solder. Determind protrusion by fitting a loose fitting wide loop in the correspondince multiplug contact, fitting and removing the multiplug, measuring the protrusion and adding about a mm.( The multiplug seems to have a certain fit play due to the rubbet seal on the control unit).
Result? No change.
Having faith in the fix went through long check list: measured/checked all relevant fuses,relays,solenoids, removed, cleaned,checked in/out voltage accelerometeors, (voltages OK. Also found out were indicator relay lives.Tip, when refitting use slightly shorter innner screw on the front one, saves skin abrasion and foul language.) Bled accumulator and duel solenoids. Checked brake fluid level.
Result (apart from quicker pressure build time)? You guessed it: no change.
Finale diagnosis came by chance. Someone pointed out my brake lights were working intermittently.
Removed brake switch plug and measure w ignition on - 12 v. Jumped plug- both brake lights on. Measured brake light switch in place - irrattic ohm values in both open and closed position.
( With great trepidation ) started the car - no warning lights or buzzer. (choreographical expressions of joy the neighbours hopefully didn't observe).
Just to check that the broken pin fix wasn't a placebo - removed it. Lights and buzzer back. Replaced it - all well.
This has worked for a month now. Since the fix I finally recieved my UDT 999 diagostic kit from Holland ( Thanks Paul and Theo). Reset the airbag lights and checked PDAS system - no fault codes logged.
A more permanent fix could be to inside the PDAS CU solder a connection from the broken pin 9 to pin 8 which is ' not used' and move the female connector in the multiplug. However at this point I dont want to mess with the CU since I understand it is impossible to find anyone willing to repair them and used ones are as rare as hens dentures, and just as expensive.
Hopefully this will give some hope if you find yourself with a broken pin.
Finałly two questions. When I replaced the brake light switch I saw to unconnected wires, one brown one brown/green with female spade connectors. What are they for? Also if you do a complete C4 bleed, do you bleed all areas of the ABS system? Under normal driving the ABS is hardly every triggered and regular use is a good antidote for failure.
































Old 09-15-2019, 07:10 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
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Join Date: Nov 2013
Location: Torquay , UK
Posts: 77
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I should mention I did order a new brake switch.

Old 09-15-2019, 07:24 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
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