boxsey911

There are lots of threads about ABS problems on here but not so many where the problem got fixed. There has been limited success with cleaning the sensors (I've done this in the past). But it doesn't seem to be a definitive fix.

So, has anyone fixed an ABS problem by actually changing a sensor? And can a sensor be tested with a multi meter to see if it's working correctly?

My C2 has developed the problem whereby the ABS light and buzzer comes on a few seconds after driving off. Sometimes, before this happens, I can feel the ABS triggering under very light pedal pressure (wheels are from locked). It feels like a rear wheel is triggering. Often if I stop the car, turn off the ignition and re-start, the problem goes away.

And, if anyone has successfully changed a wheel sensor to resolve an ABS problem, did you buy Porsche original or the Bosch version (who I guess makes them for Porsche anyway)?

ras62

Hi Steve. I replaced a rear sensor and solved similar issues. They do have problems due to corrosion around the sensor body and the hub carrier which makes them a pig to replace. My ABS still refused to work properly afterwards, I thought it was a ABS pump problem so bypassed the ABS relay to get the pump running. Not had a problem since...
Individual sensors should read about 1000Ohms but it is worth disconnecting/cleaning the ABS unit connector and also the ABS unit relays under the black plastic cover before taking wheels off.
Give me a call if you want a hand. Rob

Page 409 in the Enthusiast Companion by Streather

HiWind

Hey boxsey - make sure the relay is ok before you do the sensors.
Threads shd explain the way to bridge points on the relay safely.
If that's ok - was my problem - no need to worry re the abs sensors or their wires
Or the teeth (which the sensor uses re wheel speed) inside the hub being damaged.
You can test the ohms with wheels off the ground and spin one at a time
- also described in one of the many but scattered abs threads.

https://rennlist.com/forums/10144969-post17.html

boxsey911

Thanks so far guys. I'll take a look at that thread.

I bought a new relay a few months back (50 quid from Porsche!) to eliminate it. My experience with a bad relay is that the light and buzzer come on as soon as you start the engine. My issue is that the warnings come on shortly after moving off.....most recently as I was exiting the pit lane at a very wet Donington Park! Those were a few entertaining laps.

KaiB

Steve, I had the same problem - same symptoms.

Bought a relay, no. Bought two new sensors, no.

Only after the entire car (including the electrical harness) was stripped during the race build, and the subsequent re-wire of some of the harness did the ABS return.

No clue where the problem was.

I don't use the ABS now as it remains switched off, but it does work when the button is pulled.

(This post is actually meant to be a help, perhaps a connection beneath the relay box is snafu)

perelet

Logic in ABS controller is folowing:

1.Once unit gets out of reset it performs self test and resistance test on sensors, if error you get ABS light and buzzer right after start.

So if you have broken sensor wire or totally busted sensor, you'll get buzz right away.


2. If no error during step 1. ABS controller waits till car will reach 5mph and compares readings from all 4 sensors.

If there's significant mismatch in reading between 4 sensors - you get ABS light and buzzer. Typically mismatch in reading is because of dirty ot bad sensor. Also a lot of dirt on and around abs wheel can trigger false reading.

Oleg.

boxsey911

Thanks Kai, your ideas tie in with a harness problem I found in another thread where the guy found the harness wasn't connected to the rear sensors (a plug that is near the fuse panel). I'll look for the plug and clean up the pins.

Thanks Oleg. Any recommendations for cleaning inside the hubs?

boxsey911

I'm about to start checking the speed sensors but noticed this morning that the spoiler light is not illuminating at start up. It used to come on and then go out just after moving off as it should. Spoiler is still working fine in automatic and manual mode.

Does anyone know which speed sensor supplies the spoiler warning light? I'm wondering if there is a coincidence i.e. could the speed sensor that is firing the ABS warning also be the one that supplies the signal to the spoiler warning light?

NineMeister

The speed signal for the speedo and spoiler is an output from the ABS ecu which is a converted signal from the front wheel pickup. I think it uses the left one but not 100% sure.

HiWind

to clean up inside the hub, remove wheel (obv) and place tray under neath then liberally apply brake
cleaner spray into the hole where the sensor sits while turning the wheel (to get spray on all the teeth).
Might be able to see in with a well placed flashlight - looks for broken teeth or gunge. Drip dry and repeat.

But you've bridged your relay and that didn't work I take.

Just a random post-race-day-3rd-dram thought ... hic ... but could this be a symtpom of the mysterious "clock solder problems" ?

boxsey911

First Update.

Checked the resistance of all the wheel sensors today:

Front left = 1038 Ohms
Rear left = 1037 Ohms
Front right = 1029 Ohms
Rear right = 997 Ohms

On spinning the wheels the first three above oscillated between 1010 and 1060 Ohms (as best as my memory could could cope with whilst spinning and watching the multimeter at the same time). The rear right oscillated between 986 and 1010 Ohms.

I don't know if those values for the rear right are significant (I don't know much about electronics) but I'm tempted to replace that sensor first based on the findings.

While I was at it, I pulled the rear sensors. They were very clean. The teeth in the hubs looked in good shape (nice and shiney) but I vacuumed them out for good measure. That had no effect because the ABS light/buzzer came on a few seconds after setting off.

ras62

Those numbers are ok Steve. Did you check the connections on the ABS controller? Is this a new problem after having the floor done?

boxsey911

No, it's an ongoing one. It was intermittent for a long time. I bought a new ABS relay but that didn't solve it. It's no longer intermittent and happens every time I drive off.

HiWind

deja vu Boxsey?

https://rennlist.com/forums/7090417-post8.html
https://rennlist.com/forums/7091228-post9.html

oh, and here's another I checked .... https://rennlist.com/forums/2345228-post13.html

boxsey911

Thanks H, I checked the tail lead to the battery earlier today (looked OK) and will put the others on the list for next weekend.