bruciebonuz

Hi all,

My 1990 928 GT occasionally flashes up the "Differential Control Off" warning on the dash display.

PSD Fluid has been flushed and changed. PSD is working as it should. Green lights also come up on the dash.

No ABS warning messages at all.

The wheels have had the RDK sensors removed.

Any ideas what the culprit could be??

Thanks

Jonathan

FredR

Does this alarm illuminate when you go over a sudden sharp bump and then reset without accepting the alarm? Mine does this occasionally and I put it down to a faulty contact somewhere but have not fathomed out exactly where. If it was a genuine alarm I doubt it would reset itself like mine does.

928 at last

Could possibly be the "Lateral Acceleration Sensor" under the driver's seat. Mine was acting up a few years ago, and a flushing with DeOxit resolved the problem.

928 GT R

My 90 GT flashes the "Differential Control Off" on startup and I have to clear it every time I drive. The differential was serviced and re-sealed by Drooman, works properly and the green light comes on when it intervenes.

I will also check the contacts on the lateral accelerometer and see if that works.

Thanks for asking the question!

FredR

The accelerometer generates a measured output that is fed to the ABS computer that considers this variable and other factors to generate a control output to the PSD unit proportional to the computed need. Considering that fact I would be surprised if the accelerometer functionality is the cause of the OP's issue if the unit is working.

It will be interesting to see if anyone can actually identify the likely culprit whatever or wherever it may be.

SeanR

This is one of the bits on the car that is most difficult to diagnose and fix as there are so many items interconnected. Costs can get pretty high on them too.

Kevin in Atlanta

Remove and shake the Lateral Acceleration Sensor - if it clicks it is OK, continue with cleaning the connector. If not you can separate the housing and use DeOxit to clean it.

Edit: You can get to the Lateral Acceleration Sensor by moving the DS all the way to the front.

Mark Anderson

Or just replace it with a new one They're only $2097

FredR

Or 250 quid + vulture tax from John Speake for his offering.

bruciebonuz

I removed the sensor, shook it, it clicks. Opened it up, cleaned it with contact cleaner....will see if it makes any difference!!

worf928

Where are you? Does anyone near you have access to a Bosch Hammer (factory diagnostic tool)?

It will read the code from the PSD/ABS ECU and that might point you in a useful direction.

EGDUSA

Same issue on my '90 S4 AT. No ABS lights light -but do get the green pdk light when spinning a wheel, purposefully on a tight corner.. Trans & rear diff fluid flushed -no change. I found this which was informative. -http://www.nichols.nu/tip588.htm - Have not gotten further with it... didn't find Bosch Hammer in San Diego.

Erik
'90 AT <91K FS
'86.5 AT <115K
'88 AT 121K sold
'84 AT 110K sold

worf928

bruciebonuz

We flushed the PSD fluid, tested the PSD - all ok.

The sensor is moving freely and has been cleaned.

The green PSD light comes on and goes off.

And yet the warning on the dash comes up just during regular straight ahead driving on the highway. I can clear it with the stalk, and it doesn't come back on immediately.

FredR

Note the colour "Green"- this is an "advisory" telling the driver that the system has detected a need for some degree of lock up and is applying a calculated degree of lock up to correct the situation. It will do this in a straight line if it detects different wheel speeds as can and will happen if traction is lost.

"Bad things" like timing belt warning light tend to have red flags!