kta

Hi All. New to this forum - so glad to see the wealth of knowledge and community here!

I'm about to purchase a '91 964 C4. It has 85k miles, the last 10k are on a rebuilt engine. Overall the condition is fair (image attached). I know the owner, and they discovered a leak, which was just repaired recently. Meanwhile - we hit another snafu with the warning lights for the ABS and PDAS (I've learned this acronym refers to the traction control [please correct me if I'm mistaken]).

I spoke with the mechanic, and he mentioned that he cleaned the sensors and checked the fluid levels - after a bit of driving, these lights both came back on (before that, they were just always on). He explained the car will NOT have ABS or Traction Control as a result. He suspects that the on-board computer might be the culprit - but has no way to test it unless he can find another computer to swap and validate it. Apparently this computer is very expensive ($1k+)

I'm hoping this isn't the issue, but need to find a way to test it before committing to purchase this computer. Has anyone had this experience and/or advice?

I have another predicament which is I need to drive this car from Los Angeles to the Bay Area (California). From your experience would it be fine to take that trek (about 500miles) with the warning lights on? I may just want to take care of the issue after bringing it back home to my garage.


All your feedback is greatly appreciated.


- Kevin

budge96

The car appears to be well maintained and in above average condition for the miles I would be happy!
Most of these are in the mid 150k area mileage wise, also the engine has a rebuild ? huge
Plus !
In so far as the ABS and/or traction controlle light being illuminated should not be a problem for a 500 mile journey just be aware under heavy braking the brakes may lock up or skid ..
only under extreme emergency situations.
If I were you I'd try and gain some accommodation for the expected expense of a ABS
ECU and get on the road !
Congrats and good luck nice find , I have a GP White 993 best color...!! Bert

dlpalumbo

Did the mechanic have a Bosch 9288 code reader? Did it report the failed sensor? Which sensors did he clean? I suspect he cleaned the ABS wheel sensors.

Right after I bought my C4 the ABS/PDAS lights came on. Turned out to be the longitudinal accelerometer. In a C4, this is used for both ABS and PDAS. These can be cleaned as they build up metal filings (they're a pendulum gizmo). The action of he pendulum becomes inhibited leading to intermittent failures.

If this is the problem, I suggest you get the solid state accels that are now available. I dont have link, but I'm sure someone will chime in. The sensors can be cleaned and are also available used.

You can drive the car, but wont have ABS. You wont miss the PDAS under normal conditions.

Good luck,

Dan

spartansix

You need to have the code read by someone with the proper tool (Bosch KTS300 "Hammer" aka Porsche Diagnostic tool 9288). This will give you more information.

There is also a C4 ABS tester tool made by a member of this forum that you could use to troubleshoot the whole system if the code isn't helpful.

kta

Thanks for all the advice so far! I'm going to double check on these questions with the mechanic and report back.

Question about the Bosch KTS300 (Hammer) and the C4 ABS Tester... has anyone had experience with this tool http://www.bergvillfx.com/index.php/...4-and-993.html + the Freeware the comes with it? Can it be utilized for the same purpose of doing a diagnostic not he ABS + PDAS?

PAOLOP

Try the C4 ABS tester

dlpalumbo

You can use the software tool to read the codes. It has limited functionality beyond that.

You (or your mech) should try to borrow a KTS300. You're in an area where one should be nearby.

Other than that, consider the PDT999 clone of the KTS300. I have one and it works well.

I have an old ACER notebook with Win 98 and the OBD software. Hasn't been run in a few years (since I got the PDT999). If you're interested, I can see if it fires up.

Dan

kta

Hi All, so the mechanic does have the diagnostic tool. It reported no errors, except when communicating with this computer (image attached). I've had a little difficulty translating the terminology - from talking to the mechanic, he described it as the AWD or 4WD computer - and described the location to me (image attached - in the blue box). Does anyone know the correct name/terminology for this computer? (I know the description in the image calls it a ABS/PDAS control unit, but I want to make sure I can locate the correct swap part for testing or purchase)


All the sensors have been cleaned, fluids are level, and wheels checked. However, I don't think the accelerometer has been checked. So when the car is idling, there is no warning light until you start driving for a few minutes, and then it turns on.

Hope I'm not sounding repetitive here... still a noob. Learning about all the computers, where they're located, and their function has been quite an experience in the past day. Will definitely have to learn more about this car for the years to come.

spartansix

The part in the blue box is Porsche Part # 964 618 126 01 . It's called a "Control Module" and is the brains of the ABS system and the PDAS system. If it is actually the problem, this car has a big $$$ issue - the part is over $3,000.

Have you removed the connector and looked for missing/bent/corroded pins?
What is the actual code reported when the light goes on?

kta

Thanks Spartansix. I'll need to check w/ the mechanic about the connector/pins and the code reported. I realized I said it was a '91 - it's actually a '90 model - does that affect the PN#?

3K - yikes! Definitely sounding like A) will need to find a gracious owner in the OC/LA area OR SF Bay Area with this part or car that might be willing for me to plug in and test to validate the CM is indeed the problem B) take the car home first and start the search for the right part.

Back to getting those questions answered... I will be back!

dlpalumbo

When I had my ABS/PDAS lights come on, the tech told me it was the lateral accel that had failed. I bought a used unit, and used it to replace lateral accel.

Bottom line is that after I drove a bit the ABS/PDAS lights came back on which sounds like what you're describing. I feaked out at first as next step was either wiring or control unit.

I ended up in desperation replacing longitudinal accel with old lateral accel and lights stayed off much to my relief. I know ABS is working as I tested it under hard breaking. Dont know why the tech told me lateral accel. The longitudinal accel is used for ABS and PDAS so it makes sense this could be cause of both lights.

I opened failed longitudinal accel and the pendulum was covered in metal filings (old accels used a pendulum to sense acceleration). I have learned this is common failure mode. You can clean the filings with appropriate spray. Search the threads.

The failure of diagnostic tool to talk to ABS/PDAS control unit may not be control unit's problem. I suggest pulling the long. accel. and opening it up to inspect it before going after control unit.

If you see metal filings you know you have at least one problem. I bought a used accel. for $400USD several years ago. New solid state replacements are available for about same cost.

The great thing about maintaining an old Porsche is that parts are available. The bad thing is how much the parts cost.

Good luck.

kta

Thanks @dlpalumbo and @spartansix. Sorry for the late replies.

So both the accels have been replaced. All sensors cleaned, which leads the mechanic to believe it is indeed the ABS/PDAS Control unit - since the diagnostic tool cannot communicate with it.

No luck finding someone who would be willing to quick swap for testing, but I may have found the next best thing. When I searched the PN# which was 96461812600 - I came across some refurbished units http://www.autoecmstore.com/products/96461812600 for $1k (if you return the replacement, they'll credit back $100 > better yet, if you misdiagnose, you get a refund - however there will be a $75 restocking fee)

OR some other sites that will repair for ~$500.

Does anyone have experience w/ going the repair/refurbished route? Or thoughts? The deal sounds really good overall as opposed to buying a unit used for 3x.

Here's an image of the ABS/PDAS Control Unit - if I'm correct, the blue box is the actual PN# I should be validating to match the right part, do you know what the other two are? I searched the # in the yellow box as well, and the same company that offers repaired units even has a unit for $400 less. (0265106014 - http://www.autoecmstore.com/products/0265106014)

I'm assuming the green box # is the SN#.

2000m2

I'm curious how this turns out as my same lights come on sporadically. Sorry I don't have much to add. The codes my C4 puts out indicate the speed sensors are bad, but they've been replaced and same codes appear when the lights come on. Nice find on the parts!

cajonfan

Hi Kevin,

There are still many possible faults besides the ABS/PDAS Controller you may want to consider before swapping parts. These cars are all more than 25 years old and anything is possible.

Your last posts implied that your mechanic could not communicate with the ABS/PDAS Controller through the car's diagnostic port. Perhaps the controller is not getting reliable power and ground connections. A powered off computer works about as well as a fried one. The computer gets its power through a relay circuit that has the potential for failure. 25 year-old grounds are always suspect.

You and your mechanic need to validate that the interfaces (power and signals) between the car and the ABS/PDAS Controller are reliable and working. This is one of the big reasons that I developed the C4 ABS Test Set and its test procedure, (the other is to exercise the abs hydraulics that are never tested). Your mechanic doesn't need my unit to do this job, (he can test by schematic), but the job needs to be done.

I still have parts on hand to assemble more C4 ABS Test Sets. Please pm me if you would like additional info.

Michael (cajonfan)

2000m2

Hi Michael,

Is there someone in the Bay Area with the C4 ABS Test Set?