Vancleef

I had a similar issue with the ABS and PDAS light coming on for over 2 years. I decided to re-solder the clock, and it fixed all of my issues(had another issue of alternator not being excited when ignition started). If you have $20-30 to spend at Sears get yourself a soldering iron, some solder, flux, and give it a try. Takes a few minutes before getting use to it, but it actually became relaxing for me. I wish I would of done it sooner.

kta

Hi Tony,

Thanks for the tip! I wasn't able to get that specific contact cleaner in time for this weekend - but found something similar @ the local Lowes. Unfortunately, no dice - both the lights and sound go off after driving it (usually after ~1,000 ft - it doesn't sound off while idling)... I'll give it another pass tomorrow. I'm also going to take some of the other advice and figure out how to check the grounds... does anyone have any tips as to how one should do that? Where to test? I have a multimeter - but I'm a super noob at this, so the learning curve is about to get real steep haha!

BTW - I'm based out of Palo Alto. I heard about the EASY event, hoping I can make it in April. I haven't heard of the swap meet in SJ, but I have some prior commitments. Would love to meet up some time! Much to learn from y'all!

Thanks,
Kevin

Porsche930

Sounds good Kevin. Keep us posted on your findings.

2000m2

I've been mixed in here a bit on this same problem. The lights would come on after about 30 - 40 miles of driving from a cold start. Thought I'd chime back in now that I've driven about 300 miles without the lights coming back on... knock on wood. Here was my progression:

1. Replaced both left side speed sensors, per the codes that were coming up. Lights came back.
2. One night every single light on the dash light up briefly and went out, so back to shop (Christmas tree lights). Found holes in the caps and bad ignition rotors, so replaced those. Running pretty smooth, but the lights came back on.
3. Replaced both relays on the ABS pump. Lights came back after about 30 miles of driving. Engine running rough again.
4. Shop found bad spark plug connection at #5 exhaust connector. Reconnected and performed system adaptation (higher idle). Running incredibly smooth and no lights for the past 300 miles.

The only explanation I can come up with for the spark plug connection issue is the PPI when I had the compression and leak down test done. That shop must not have put things back together again properly. This problem started when the previous owner picked up the car from the PPI. Seller agreed to pay for the speed sensor replacement. Anyway, frustrating stuff, but the car is running super smooth now and is a pleasure to drive.

kta

Hi Tony,

Will you be at the EASY meet tomorrow? I'm going to try and drop by for a little bit in the morning.

Also, I finished my test with the multimeter - found the following:
1. The grounds to the PDAS unit all test OK
2. Brake fluid is totally full - the sensor tested OK
3. Mechanic cleaned and tested all the wheel sensors + accelerometers > so I didn't open these up myself - assuming these are OK
4. He also reported the Bosch tool could not communicate w/ the PDAS system itself. So I checked the grounds from the connector for the Diag tool (on passenger side) all the way to the correct pins on the PDAS... that wiring tested OK

Per 2000m2 - I'm not sure where to check that Spark Plug connection (nor the symptoms that would suggest I check that), is that something from the finding's above you'd recommend to look into?

On a bright note... wiring seems to be good. Everything seems to be getting or at least capable of getting sufficient power. The battery and alternator are solid. So the last thing is that darned PDAS... I might need to find a local mechanic to run that test one more time to see if we can communicate via the Hammer/Bosch tool. Otherwise I fear it may indeed be a bad PDAS unit.


Thanks,
Kevin

Beezztie

Does anyone know the numbering on the connector of the Bosch ABS / PDAS unit? Do not see any digits on the connector and also no view in the workshop manual.

968workaholic

Beezztie

Great, thanks!

LM964

My recent (PDAS ECU pin corrosion) cross-thread which hopefully helps...

https://rennlist.com/forums/964-foru...l#post14104973

Beezztie

Thanks, responded on your thread, exactly what I also encountered (only in my case pin 11 broke off on the PDAS unit..)

kta

Resurrecting this thread. Almost 3 years later of driving the car which has been so fun! Car feels and runs great, have done some general maintenance (gaskets, boots, tie rods, etc.) I've brought this car two mechanics for general service/maintenance and to do an initial attempt at getting the ABS light off. It's still unclear what the cause can be, but to summarize what we've gathered so far.

1. PDAS contacts are all good
2. Grounds to the PDAS are good, as is the wiring running from the passenger side all the way to the PDAS unit in the frunk
3. Accelerometer Sensors are replaced / "good" but below is a contradictory result from the the Hammer
4. The mechanics said the Hammer could communicate with he PDAS. At the very minimum, that means it's not dead. But the following errors were coming back after resetting it and taking it for a drive (the lights and beeping come on usually within 100 yards), but the've both reported the same errors from the Hammer

• Error: DME code for Knock Sensor Bank
• Error: Code for ABS Longitudinal Acceleration Sensor
• Error: Code for Control Unit Faulty (I believe this is the ECU)?

5. Brakes have been bled
6. Also a correction in case it's important this is a 1990 964 C4, not a 1991

Focusing on #4, one of my mechanics said it might be the ECU and will require to repair it (~2k+ job, yikes). But we're still not 100% certain, and both mechanics said they'd still need some time with the car to really find a root cause. As I've read, sometimes what the errors/lights say doesn't pinpoint the root cause and overflow to create other signals/errors, so don't go repairing/replacing items until you figure what that is!

That said, per the error code summary above... has anyone had a similar experience or have some thoughts to what else could be causing the ABS light to turn on, before I bring it back to my mechanics? That bright red and orange light are starting to annoy me :P

spartansix

What is your battery voltage:
Car Off?
While Cranking?
At idle?
At 3000rpm?

kta

Had so much time during the lockdown. I got to reading, picked up some tools and braving up to some DIY. Checked the accelerometers myself - even though the mechanic who maintained the car before I bought it said they cleaned them... and found them filled with shards. Got them cleaned up and now, now more warning lights! Huzzah!
This is old, but wanted to thank all the folks who replied.

2000m2

Nice work, congrats!

kta

Got those darn ABS + Diff lights coming on again - they go on after just driving a 100 feet, to as far as 1/4 mile. I just did an oil change and brake bleed. Brake pressure feels normal, but I did notice early in the drives after a few hours of being parked OR after shutting off the car - waiting 30-60 seconds before starting it back on again - when I drive slow and reach a full stop, the brakes blips a little and travels a few centimeters to 1/2 inch right before the car hits that full stop. Braking is still normal, just my foot travels on the brake pedal as the blips occur. It kind of feels like what happens when the ABS kicks in. I've never felt that on this car before, but on my daily (Prius) it happens when braking quickly on a patchy road.

Brake fluid levels look normal - right up the max while the car is on. It's above max when the car is parked for a while, but I'm guessing that's because the accumulator is not primed while the car is off?

Has anyone experienced this before?

Here's an image of the warning lights. The "!" is off on purpose, I've been trained to hit the button to stop that beeping sound at the drop of a dime now.