ABS/PSM-issues, again...

Last year my ABS/PSM started to interfere during normal driving conditions for no apparent reason, without setting of any lights. This was just before I parked the car for the winter. This weekend I got back at it by replacing the front left side ABS-sensor and reluctor ring (the old ring was badly corroded and cracked), but this didn't solve the problem. I'm tempted to replace the front right ring as well, since I ordered two replacement rings. The front right sensor was replaced during summer 2018, and has only a few hundred miles on it. I came across a thread here by Alex (?) which described how to measure the output of the sensors with a multimeter, so I tried that today. I'm not sure about the values (and I can't find the thread!), but all sensors gave a signal. Any help or advice appreciated!

http://911uk.com/viewtopic.php?t=127602 http://911uk.com/viewtopic.php?t=109245

Its a bit tricky to use a multimeter on each sensor and get an accurate reading .. A scope is best but unless you can get an accurate reading of the amplitude then again you won't be able to diagnose a reluctor ring . I find the best way is just a visual look at each one .. there should be a clear gap between each segment .. that's what the car sees .. If corrosion is obvious and staring to make there be no gap in places then the car thinks at that point the wheel is locking up .. hence it applies the abs . I tend to find driving at 10 mph and light braking is when this type of fault will be more obvious as the abs will kick in .

Alex, that thread was exactly the one I was looking for :mrgreen: Thanks, deMort. I think I'll go ahead and replace the right front ring as well, as it is every bit as ugly as the cracked one I replaced this weekend. Even if it turns out to not be the source of the problem, it won't hurt!

[deleted... solution I proposed was not for the issue described]

Just got back in from the garage after inspecting the rear reluctor rings and measuring resistance in the ABS-sensors. Both rings look intact, but the sensors read 1.54 and 1.55 respectively (both front sensors read >1.6). They both look like they have been sitting there for a while, and I suspect that they won't come out without some heavy persuasion. If working sensors should read 1.6 or above, is it plausible to believe that they are causing the trouble?

If all 4 sensors read about the same resistance then i would lean towards they are ok .. the way they work is by generating a voltage .. basically an on / off signal . The gaps in the reluctor rings have far more bearing on a fault or not .. these generate a voltage by having a lump of iron moved in front of them .. if the lump is big enough ( no gap ) then it sees a problem . 1.5K ohms and 1.6K ohms is pretty much the same ( probe multimeter contact can make a difference here ) .. a problem would be in excess of 3K ohms or 50 ohms short circuit .

That sounds logical. Tonight I'll have a crack at the reluctor ring on the right front shaft, as I have a spare one laying on the bench. As I mentioned, it looks just as bad as the one I just replaced on the left front shaft. If it's still working it it's current condition, it will probably just be a matter of time before it needs to be replaced anyway.

Front right reluctor ring... despite what I posted earlier, this was not as bad as the left one, but I'll still replace it tonight! It was actually sort of disappointing to find that it was intact, because replacing it will probably not solve the issues :roll: I might just go on and replace the rear ones as well...

I don't suppose you have any king of tester to read fault codes or see the values of the sensors ? It's just that you have replaced one ring and this ring doesn't look to bad so im thinking it might be something else . Just a thought but logically as the sensors heat up then one might intermittently fail .. you would have a fault code saying this .

I don't have immediate access to a tester, but I'll have my friend send me his! You are right. Perhaps an intermittent failure from one of the rear sensors or even the harness? As stated earlier, no lights of any kind.

My friend is sending me his Durametric, I'm itching to get some readings. In the mean time, I need to sort out my brake dust shield. Yesterday I figured I'd remove it to get some headroom when working on the reluctor ring replacement, but two out of three bolts snapped (of course). The shield is still (barely) held in place by the last bolt, but I want to drill out the broken ones and replace them. In order to access them and get a straight line for drilling, I need to remove the wheel hub. Firstly, is it a matter of simply undoing the four visible 13mm bolts holding the hub to the carrier? Secondly, I expect them to be seized up. Is there a risk of damaging the wheel bearing inside the carrier if I apply some heat to them?

If you remove the hub you will pull out part of the wheel bearing .. that would mean a replacement wheel bearing is needed. Video here of it being removed but if you look at the end of it you will see the bearing race is still attached to the hub . https://www.youtube.com/watch?v=Opa63-Fi_Ck

I just read an article about it on pelican the moment you replied. I do not intend to replace the wheel bearing just yet, so I'll have to think of something else :what:

There is no chance in h*ll to drill out those broken bolts without removing the hub from the carrier. It will have to wait until the wheel bearing needs to be replaced. I managed to keep it in place using a ziptie and the bolt that did not break. God, I feel like a redneck😣