marnsue

Please help! My 99 C4 ABS and PCM does not work.


Symptoms:
- ABS and PCM doesnt work. Even though, there are always two codes, no ABS warning lights are lit, while the car is on.
- If I pump the brake pedal quickly and heavily couple times, on the second or third "pump" I get to engage what feels like the ABS pump pulsing. I attached a video to better understand what i mean.

Codes:
5024 - CAN message missing from tiptronic (this is a 6-speed manual?!)
4266 - Return pump fault



What I've done:
- New brake booster (only thing that was done by others)
- New brake position switch
- Refurbished ABS Pump
- New MAF sensor
- replaced ABS/PSM module with used one, same part number.
- checked ABS relays (resistance, and applied 12v to assure they click)
- checked speed sensors by measuring correct resistance (there are no speed sensor codes)
- bled the brakes several times
- checked the ABS/PCM wiring harness following the service manual procedure, also OK

Here is the video. You can hear that the ABS pump continues to work even after the car is at a standstill and not moving.


A little background, which may help with ideas:
WHen I bought the car, everything was feeling great, and even one fellow porsche owner that drove my car 2nd day after purchase mentioned that brakes feel great.
Within a first few weeks of ownership, Ive brought the car to Freed performance to look things over, and among other things theyve done, one was replacing brake booster as they stated was failing.
I also requested brake flush as the fluid was very cloudy while they were at it. Once I picked the car up, the brake pedal was below the gas pedal and brakes felt very weak, so I brought it back, theyve adjusted the pedal and checked the brake performance, which they said was in par with other 996.
Once i brought the car home, i thought, that it just needs to have the brakes bled some more, so Ive started on the rear right caliper. To my shock, the fluid that came out was ugly, cloudy and had a few bubbles that ive seen come out. So I brought the car back, and had to bring the extracted fluid with me as theyve claimed, they have flushed the system.
On the following test drive with the shop owner, there was the first lock up ive noticed. He mentioned that its weird how it locked up. As i was done with this shop, I just took my car and stormed away.
I sadly can not be 100% sure that the ABS problem was there before this brake work, but the way I and couple friends that drove it indicate, there wasnt any brake or ABS problem.
That is where my hunt to fix the ABS started. Almost 2 years ago.

Reason why Ive never brought it in anywhere else, is after the disastrous experience ive had in the first shop Ive simply lost the trust for any "expert" to do honest work. For instance, among other things, I requested and was billed for OEM brake booster, which ended being cheaper, not OEM booster.

It might help to mention, that if I press or hold the PSM button, there are no changes, nor any lights that come on. Before the start, once the key is in ON position, all the brake related lights come on, so there isnt a LED or a lightbulb that would be out.

pdxmotorhead

I didn't think you could bleed the system without a device to turn the pump on while your doing it?
any air in the pump and it wont work correctly, and very quickly eat itself up..

You need to find a real shop and don't play the I was burned once game,,
you should be able to find a good suspension shop at any Porsche club track event..
There is almost always a "guy" in a town with a track and hes likely not a "P-car " guy but a
german car guy..

billh1963

I agree

The shop you used was incompetent....period. I seriously doubt your booster was failing. They were looking for "low hanging fruit"....easy things to change to make money. Unfortunately, they couldn't even do that properly.

Post what city you live in and some members will chime in with competent 996 shops to use. Your problem(s) will get resolved

Porschetech3

Sounds like you have installed a used ABS/PSM module from a TIP (needs to be recoded for 6MT using PIWIS).

Also probably needs to be properly bled using PIWIS to activate ABS pump during bleeding..

marnsue

Aha! That makes perfect sense. Ill have it done, and report back. thank you

808Bill

Any update?
My ABS/PSM warning just came on a few minutes ago on the way home.

Mike Mullins

check your brake light switch first

Dr_Strangelove

I also have had ABS/PSM from a rear wheel speed sensor that had come loose with the vehicle in motion when the dumb mechanic didn't put it back on tightly enough.

(I'm the dumb mechanic, btw.)

Edit to say that this is probably more helpful for 808AllDayBill and not OP.

808Bill

Lol, I haven't touched that one yet...Thanks!
Mike, Brake light switch is on the shelf and next to go in.

808Bill

Brake switch is in but I still get the ABS/PSM warning. Guess I'll try cleaning and or swapping MAF's.

Porschetech3

Make sure the brake light switch is adjusted properly.

The ABS must "see" brake light activation BEFORE it "sees" brake line increase in pressure....IF it "sees" brake line pressure increase FIRST, it will set a fault.

808Bill

How is it adjusted, pull the plunger out further? It's a bitch under there!

Porschetech3

Just push or pull the" body" of the switch in the bracket, it will "click" up or down with a little force.

Adjust it so that as soon as you touch the pedal 1/8", the brake lights activate..

If you have Durametric, you can watch actual brake line pressure and brake light activation simultaneously.

808Bill

Update
The switch I had sitting on the bench didn't work and turned out to be a clutch pedal encoder switch I ordered awhile back. Put the old brake switch in and replaced the clutch pedal switch and viola, no more ABS/PSM warning...At least for now.