Doug&Julie

I recently had my CV boots and my windshield replaced. Ever since these lights will stay on longer than any others at first start up. They go out after about 50 feet of driving, but this didn't happen when I bought the car, so...not sure what to make of this? I believe it's the front diff light and the ABS light. Also note the little light on the front diff switch is also on, but also goes out after about 50 feet of driving. Thoughts? (Sorry for the cell phone pics, I took them in the dark this morning!)

Rocket Rob

I would confirm that your brake fluid reservoir is at the max. If its not, these lights will illuminate. Do you also hear the ABS pump running while they are on? This is the ABS system charging the pressure tank. Do a search for bleeding the tank.

Not sure why changing the CV joints or windshield would cause this. I suspect its a coincidence.

doug751

That only means that the hydraulic Bosch pressure intensifier (bomb) for the all wheel drive and ABS is pressurizing. Most of these C4's will do that for about 10 seconds or less when starting cold. You can hear the pump right when you turn on the ignition before starting the engine. It is located under the hood, hidden behind the plastic cover in front of the battery.

Another test is to wait until that pump stops while sitting still. Then pump the brakes fast. You should be able to pump those brakes at least 7 to 10 times before the intensifier starts again. If the intensifier starts right away after 2 or 3 pumps of the brake pedal, then you may have a problem. The actual test with the correct number of pumps and timing is located somewhere in the Porsche 964 repair manual.

You must flush / bleed the bomb and the rest of the hydraulic system occasionally. I have done it following the exact procedure in the shop manuals. I am not a mechanic, and it is not difficult, but is tedious and makes a mess. I bet that most mechanics skip this and many C4 have never been bled. It has been 9 months since I did this and I do not remember the exact procedure.

Perhaps somebody with more experience could provide a clear procedure?

Doug&Julie

Thanks for the quick replies.

Pardon my ignorance, but would that have been done with either of these services?

"Flush and renew brake fluid and AWD system"
"Replace front differential pinion seal (moderate fluid leak),
change front differential fluid."

Rocket Rob

Maybe this thread will help.

https://rennlist.com/forums/964-foru...placement.html

Doug&Julie

Thanks! Also found this thread FWIW...

https://rennlist.com/forums/964-foru...ing-lamps.html

Makmov

If you read the owners manual it will state those lights will illuminate until the system has reached about 7kps. It sounds like it is behaving normal. The diff lock, it probably means it been manually put in to lock mode which will disengage at some mph. It is for use when you get stuck to lock. You probably just need to unlock the front diff, IE no light. Also sounds normal.

Makmov

Yeah, on a C4 you cannot just bleed the brake like on other cars. You need to do it through a scan tool that electronically allows a properly.

doug751

You can bleed the brakes and clutch on a C4 without a scan tool or hammer. You just need a power bleeder that pumps-up to pressurize the fluid in the reservoir.

You can flush the intensifier (bomb) without a hammer or scan tool, you plug and unplug the power to the pump in the process and collect fluid from nipples in the manifolds. Things must be done in the proper order to prevent burning up the pump by running it dry. It is best to buy the manual and do it exactly as they say.

You CANNOT bleed the differential locks easily without a scan tool or Hammer, but there is a way to fudge it by shorting out some contacts or using that switch in the center console to lock the differentials. I have not done it that way but have heard about it. The Hammer is normally used to pulse the solenoids while you bleed the differential locks at their nipples. This is not a technically challenging job, but it is a pain to remove all to covers and reach inside there. If you are not careful you will spill brake fluid on yourself and you could also strip the nipples which would make for a really bad day.

Doug&Julie

So update after spending some time snooping around...the good news (?) is that my brake fluid reservoir is at max. And after a quick visual check I could find no leaks around the system. So after the car sat for about an hour and a half I turned the key, got a noise that sounded like what you guys are telling me to look for (a whirring noise coming from under the black plastic part covering the ABS unit, if I understand correctly). After a few seconds it stopped. I looked back in the cabin and the lights are off. Cool. I turn off the ignition and head back into the house. Then I think, I should verify this happens when the car is running. Go back to the car, turn the ignition on and hear nothing. And now the lights are on. I didn't drive it, just shut it off and came in.

Soo....

Does the lack of noise the second time happen because it was fully pressurized from the first time? (i.e. it's ok?)

Does this mean my lights mean something different?

Is there a relay or something "simple" that could be causing this? (My DME is brand new, FWIW.)

I guess I need to get this thing bled. I don't think I'll try it myself. Too new to these beasts.

Thanks all.

Makmov

You have actually start the car for the lights to go out. If the light stays on while it is running then there is a problem.

Lil bastard

You're obsessing! These lights are supposed to come on for upwards of 30 seconds after you start the car as the system repressurizes itself - It is NORMAL. It can take longer if very cold, but not more than say 60 sec.

The service you had performed is what got the system working again. Why didn't it work before? Loose electrical connector, corrosion, needed flush/bleed etc. Jostling or replacing the connectors did the trick.

It's a case of TADTS - They All Do That Sir (or at least are supposed to).

Cheers!

aeroman

I also get the loud beeping almost every time I drive the C4 either right away if it has sat for a few weeks or as much as a half block from the house. It last for 5-10 seconds and then goes away and the lights go out.

Doug&Julie

OK then...ignoring the lights from here on out...

Cheers!

Makmov

That is a level 3 Central Informantion Warning alarm, likely for the ABS. Annoying thing! Mostly they were just unplugged.