Jfrahm

Hi, I have the dreaded 'Antilock' warning on my 1987 928S4. The light comes on right away, so I know it is not a gunked up sensor. It might be a disconnected or bad wheel sensor though. I could ohm the sensors and/or look for AC voltage from each at the brain if I knew which pins on the brain went to the sensors. Does anyone have this info handy?

Thanks,
-Joel.

Jfrahm

*bump* is this info in the service manual? I could dig it out of there I suppose.

-Joel.

Greg86andahalf

6 4 -LF
21 23 -RF
8 9 -LR
24 26 -RR

Jfrahm

Thanks Greg!
-Joel.

athenian

Joel,

Please post your test results here and let's us know of the progress...My '86 has the same ABS problem and I have cleaned the sensors, changed the relay (used a good ABS relay from another car) and traced all the wiring....The ABS light is still on but the ABS functions work well!

Regards

VK

Jfrahm

Working on this now. I'm Having some trouble with Greg's pinout, I think the right front wheel sensor might be 11 and 21, and not 21 and 23, but my .pdf manual is not clear enough to be sure. I've found around 1k ohm beween the other wheel sensors and 1k ohms between 11 and 21 also. Off to try to see AC voltage while rolling.

Jfrahm

OK I think I have the pins right and I got voltages:

1987 928S4 AT rolling at 5mph or so (iding in Drive)

Pins wheel Volts

_6____4__LF___.73 volts
21___11__RF__1.0
_8____9__LR___.76
24___26__RR___.75

Voltages go up to around 1.4 VAC at 10mph

I seem to have connections and acceptable output from my wheel sensors. Anyone have a known-good ABS relay I can borrow or buy? Is there a diagnostic procedure for said relay?

Thanks,
-Joel.

jon928se

I'm about to do this but I can't seem to see pin numbers on either the ABS ecu or the Connector/plug ? or do i have to take the cover off the connector to see the rear of the pins ?

Edit - yes you have to take the cover off and it helps to read the whole thread !!! . I also concur with Joel's assertion that 21-23 are not the RF pins (as originally stated by Greg - probably from the ABS testing plan for 86 up to PSD equipped cars ) - nothing connected to pin 23. However WSM page 97-299 indicates 11 and 21 as per Joels assertion. Now to start testing .

mattipuh

quite stupid question, but being a newbie on this thing, it's open to me.
Do you measure the wheel Volts from the unit connector with pins defined, running car slowly?

is there somewhere defined the required Volts from sensor which is required to ABS to work? what are limit values for Volts?

John Speake

With the sensors disconnected you also need to check if either pin of each sensor is shorted to chassis. This can happen when the sensor is crushed by corrosion. The output volts may look OK, but the short to chassis will result in the warning light.