1990 porsche 928 s4.

[happyhenry]

I have just removed all 4 standard wheels and refurbished them. After replacing them on the car and driving off the ABS warning display came up followed by the PLD warning display.I then took off each wheel to inspect the sensers and look for any damage i may have done but could not see anything. I have obviously done something any ideas?. I had 2 new tyres put on the the front whilst the wheels were off. Could you tell how the ABS works, does the 2 plastic diamond shaped objects fitted to the inside rim of the wheels have anything to do with it.Where do i find the ABS unit and relay? Hoping you can help. Thanks.

[nuc]

If the ABS light comes on after driving a small distance it would be a sensor. If it comes, and stays on after starting car but not driving, look to a relay. A quick way to check for a possible bad sensor is to ohm them out. They should all show "some" continuity, all within a narow range. If there is no continuity then check the wires up to where they go into the sensor. If you find the break in the circuit you found your problem. May be a broken wire under the insulation. If the wires are ok then you have a bad sensor. Replace and problem should be taken care of.


ABS relay is on the CE panel. Along with 2 relays on ABS pump, itself.

[happyhenry]

Thanks for the info. I am not clear what Ohm it out means Would you describe the procedure as this is new stuff to me. Thankyou.

[harborman]

Originally Posted by happyhenry

Thanks for the info. I am not clear what Ohm it out means Would you describe the procedure as this is new stuff to me. Thankyou.

I think he means to put an Ohm meter on the sensors/wiring and read the resistance (ohms). You can buy a meter at Lowes, Radio Shack, etc. Usually a combination Ohm/voltage/amp meter maybe around $25 or so for a cheap one.

[Maleficio]

Amazon.com: How to Test Almost Everything Electronic (9780830641277): Delton Horn: Books

[nuc]

Hey Henry,

Definately learn how to use a multimeter if you plan on doing repairs/maintenance to these cars. They were ahead of their time and over engineered. It seems as they get older more and more electrical gremlins pop up. Usually it is something relatively simple, but does require diagnosis.

If your up to a gratifying challenge, these cars are it.


'84 Euro 5 sp.

[happyhenry]

Hi,
I think that is good advice,i will buy one tomorrow. However how will i be able to test the senser cable when the senser head appears to be a sealed black plastic unit held on a metal bracket behind the brake disc at one end, the other end is ok as it unplugs and a metal contact is available? Or am i missing something. Your advice is much appreciated.

[SeanR]

You said you replaced the tires on the front, did you replace them with the same sized tires or go different? Changing the rotational size can upset the ABS system.

[nuc]

Unplug the connector and verify there is continuity between the two ends coming from the sensor. Do this for all 4 corners. You should see a reading which is similar for all 4 sensors.

If one of the sensors shows an open circuit (no continuity) that is a problem. Take your DVM probes, they have sharp tips, and probe through the wires insulation, as close to the sensor as you can get. If you are still showing an open circuit, the sensor is bad.

If you do show continuity when checking at the sensor, then there is a break somewhere in the wire frome the sensor to its connector.

Do some further probing on each individual wire until you find the break. Then buy a new sensor $$$$$, or cut the wire before the break and solder/shrink tube a new piece of wire. You can reuse the connector.

HTH


'84 Euro 5spd.

[happyhenry]

Hi,
I am now off to buy a multimeter that is if the store is open we have a public holiday today due to the Royal Wedding.
In answer to SeanR yes the new tyres are the same size as the old ones.

Thanks again,i will keep you informed.

[Landseer]

Thanks for the procedure. I need to do this, too.

[happyhenry]

Hi,
I now have my new Multimeter. I have unpluged the short lead from the magnetic senser at each wheel and placed a probe on the end of each wire inside the plug.
The readings are
front wheels, 10.52 and 10.30 and rear wheels, 9.99 and 10.28
I take it that the sensers and their short cables and end plugs are ok as the four readings are quite close?. Does this mean that the problem is further up the line? Thanks again.

[Mrmerlin]

you may have damaged the wheel sensors when the tires were replaced or in the painting process