Having done lots of work on all four corners, having put everything back on the car, i am getting warning lights for 1) pads 2) ABS 3) Diff control.

I had a quick look at the ABS fuse and relay, and they look OK.

I am thinking i may have an issue with a sensor (or the connection to a sensor) in one or more corners. But I have had a look and I cannot see any visual sign of an issue: the cables all look ok; the connectors all look ok.

I have not seen a procedure to detect which (if any) of the sensors are the issue.

What i wandering about is to get the car back up on axle stands, remove all 4 wheels, remove ALL ABS sensors, and then add one back on at a time until i get the warning message.

But I am guessing if you remove a sensor, it will initiate the warning message. Do i have to mimic a sensor by having a wire run from one pin on the sensor connector socket to the second one?

Is there a procedure described somewhere to do all this or a procedure to follow?

 

In what condition is the battery of the car?

 

PSD diff control warning can also cause the ABS warning, while nothing might then be wrong with either any ABS sensor nor the ABS mechanics nor the ABS ECU controller (which is a shared ECU that also controls the PSD).

Check your PDS fuse and relay first before going after all things ABS related, both are hiding in the spare wheel well - have a read "here": https://rennlist.com/forums/diy-928/...procedure.html

 

Thanks for your reply. The battery is pretty new and full charged, so i don't think that is causing the issue,

 

Hi. thanks for your reply. I have just finished installing and commissioning a rebuild PSD. As part of that work, i did have to replaced a blown fuse, but once that was sorted, the PSD behaved correctly, allowing me to prime the reservoir and bleed the slave.

 

So, i have taken all the wheels off and examined the sensors. They all look OK. I did a check on them with a multimeter. ALL of them behaved the same - i measured the resistance, and it showed "1" i.e. no connectivity, but when i spun each of the wheels, i got a small voltage.
I put everything back together, and retested, but unfortunately i have got the same messages.
What do i do next, what checks can i do?

p.s. the warning light comes on when i start the engine, but before i have moved off (i haven't tried moving off yet!)

 

Ian,

A wild *** guess to nothing here but have you accepted the alarm by flicking the stalk on the steering column? As I understand the system [and that is not saying much] if an alarm displays on the digi dash annunciator the system stays in the alarm condition until the alarm is accepted. Now, because the sytem has been in disarray during your workover, I am wondering if the brains thinks an alarm condition exists and has thus been annunciated, if so maybe that alarm will stay active until it is reset. Given alarms on the digi dash are quite rare, maybe you have simply not experienced such before and possibly not aware of this.

Heck it is so long since I had an alarm I am not sure I know what I am talking about in this instance- I think you have to pull the stalk towards you to reset the alartm and I am not even sure of that due to brain fade!

Last time I had an alarm driving was when the motor threw the ac belt and that derailed the power steering and alternator belts and the panel lit up like a Christmas tree with seemingly several alarms going off and I seem t remember flicking that stalk to cancel the alarms- hopefuly someone will correct me if I have this wrong as could well be the case.

 

Hi Fred.
I got very excited when i saw your note, as i wasn't aware of this feature. I looked in the instruction manual and followed the instructions. It does clear the error but only temporarily. If i turn the engine off and turn it back on, the error reappears.
More investigation needed

 

The latest is
1) I have retested all 4 ABS sensors with a multi-meter. All of them behave the same, all with about the same level of resistance.
2) I have tested the connection from the ABS sensors. All of these have the same level of resistance, which implies no broken/shorting cables
3) I have swapped the ABS relay in the CE board with a borrowed one.
After all this, i still have the same ABS error and the same Diff Control error.
I am having trouble getting access to the ABS pump relays (the cover will not come off, which makes no sense). I have borrowed some of these relays to try swapping those.
I am really struggling to know what to test or investigate - as the car cannot get an MOT until the errors are sorted, so the car is not legal to drive.

 

Regarding your latest:
1 and 2) What was the value as you measured? Should be around 1024 ohm, while infinite when measured to ground (IIRC: if any of the ABS sensor wires are connected to ground, the ABS/PSD ECU will shut off).
3) Although in your 1st post you did mention that your ABS fuse look OK: have you swapped the fuse for a measured OK and new one? As looks can be deceiving (I once had a distributor cap that looked and even measured OK, while it was not...A very long Rennlist thread I had ongoing due to that, trying to root cause fault find stumbling under acceleration and idle...).

Do you have access to an ECU testing tool, like the official Bosch "hammer" or a 3rd party aftermarket tool (as I have and use), thereby being able to read out the error codes of the combined ABS/PSD (and all other) ECU? As that would be my next point of action...

 

Well if nothing else that possibiity has been eliminated so the field of possibiity narrows a little.

Arnaud has beaten me to my next suggestion- an alarm on the digi dash will trigger a log in the fault history and the next obvious step is to analyse such- if you have a good contact in your local Porsche dealers maybe they would be kind enough to put the diagnostic scanner on and read out any fault codes but given they probably would charge you a tenner to take a leak these days a freebee scan read is probably not in their vocabulary unless you are a valued customer.

Hopefully Alan might just see your thread and chime in with one of his gems.

Rgds

Fred

 

hi

1) the sensors all measured around 1025. I have not measured to ground
2) i have noted 19.5 measurement on the connector pins (the pins that the sensor connects to). I can't tell you what units that was - but it was consistent. I need to try again to see what units. However, that is certainly not 1025. Does that imply a specific issue? From the wiring diagram, it looks like each pair of wires each have connectors to the Central ABS "Computer".
3) I have checked both fuses (ABS in CE Board and PSD in battery compartment) with multimeter and they have continuity

From talking to my local 2nd hard Porsche parts dealer, local Porsche dealers don't think a 928 is a real Porsche! There are some independent and mobile Porsche specialists, but none nearby. If i could get my hands on a diagnostic tool, i am sure that would tell me what i need to know, but i can't see how to get to buy or borrow one without parting with an awful lot of cash.

So, on my list to try next:
1) test to ground from sensors
2) what are the units of the 19.5
3) acceleration sensor under seat - does it rattle, give it a clean
4) ABS pump relays (i have borrowed some others)
5) I might be able to borrow another ABS computer from 2nd hand parts dealer, so i could swap that out

anything else i should try?

 

I measured the sensors again today and i found one sensor was connected to ground (!). Having taken it off, there is a bit of damage, so i have ordered a replacement. I am keeping my fingers crossed. The other 3 sensors had no connection to ground. The "19.5" measurement was 19.5 k Ohm connection on the cable i.e. very different from 2025 Ohm (no "k"), but i am hoping that is not an issue.
Until i get the replacement, i will leave this issue for the moment.