996 C4s PSM Failure / ABS Failure drive to workshop

Bought a 2003 C4s Manual back in May. Bought it from a local Irish independent dealer who sourced the car for me. On the test drive it had a PSM/ABS fault, I was told that it was an ABS sensor, that would be replaced before I picked it up. Sounded fair enough, it needed some paint touched up too so a deal was agreed with thos things fixed. Collect the car a week later and within a mile, PSM ABS fault shows up. Call back and he agrees that obviously it needs to come back in to get fixed. PITA but no big deal he will get a new ABS sensor. Oddly the fault seems totally intermittent, light goes off on restart and returns every couple of days. No stored codes, i had it scanned to see. Car goes back and gets another new ABS sensor, they test drive it, no light no stored codes. When I get the car back the day after a get a loud beeping on startup. Really loud. ABS/PSM light not on and he informs me that they are not connected as they run off a different system. Reading on here, the alarm is a brake pressure alarm. No ABS/PSM fault at the time, so I keep going. PSM ABS light comes back, so it goes back to dealer for inspection, they change some more ABS sensors and agree to look at front suspension. which is making noise. They never get the alarm but chase the ABS sensor issue and claim to fix it. They get the car 3rd July keep the car for nearly 10 weeks (I owned it it 6 weekswhen it went in) mostly waiting for suspension parts (i have a wanted ad on here looking for front spring washers). Since the parts are unobtanium I take the car back until we can get hold of them. At least the other issue is fixed.................... Pick up the car this afternoon and within 10 miles, ABS/PSM fault comes back. Obvoiusly i'm raging, but apart from wanting to set fire to the thing, I just want it fixed. Problem is I think my warranty option just doesn't know how to fix it. So can anyone think of a cause of the fault that isn't just ABS sensors cause I have to believe in 3 attempts and more than 10 weeks the garage in question have tried sensors. Errors seem to only come on for me. Still intermittent, still really annoying. Many thanks Rory

The wiring looms to the sensors can break in the wheel arches giving intermittent faults, it often happens after going over bumps. Porsche do repair kits. I wonder if the garage has checked the wiring for continuity while waggling it in the wheel arch area?

Could be umpteen different things. First job is to measure the resistance of each and every wheel speed sensor and make sure they are all in spec. Reluctor rings. Then check your brake and clutch pedal switches and make sure it's not that. Could also be your steering angle sensor. Also check for vacuum leaks, PSM hydraulic unit, weak battery, even a dirty air filter. After that you're in to suspension parts, etc. Have you identified what triggers the lights to come on, eg: hitting 15mph, turning right or left, going over uneven camber, braking, changing gear, etc?

Just to point out that I had an intermittent ABS/PSM fault from a weak alternator...

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Get your self a cheep obd dongle and app and graph the live data from the wheel speed sensors . I use diag zone and the porsche sware for it was like 7 quid .

Please post the link for the software that enabled you to do that.

Thanks for all of the advice. It's a huge help. Unfortunately I seems like a long list but I will start working my way through it. Light came on again on way to work, light right hander without touching the brakes. I'll keep a note of what triggers it. I had a full inspection done while under warranty elsewhere for peace of mind about Bore scoring and had a look through thew report to see if it corresponded with anything mentioned above. The only overlap is a reported rubbing on rear driveshaft reluctor rings. Pic attached below. Might not be it, but reluctor rings were mentioned. Other as i mentioned its getting new front suspension once I find the missing parts, current set up is aftermarket and too low, so it's going back to standard.

My C2 had an ABS issue on the rear, It needed a new sensor & reluctor ring. The opposite side ring was also shabby and benefitted from replacement.

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Diagzone.com - Diagnostics for everyone diagzone.com I usee a golo dongle . I use it on all my cars without issuse . Worked better than durametric for me .

To me this looks to be cut and shut case and iv no idea why it wouldn't be the first thing they changed . It needs a new drive shaft . That picture you posted would 100% screw up the abs .

The reluctor ring is separate from the driveshaft. You'd just need a new ring.

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Learn somthing every day . It looks like it would crumbed trying change it though.

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I know this might sound a bit daft but have you checked your tyre pressures? For it to be ok and then come on after driving a mile or so, I'd guess it's actually something wrong with the car and not the ABS/PSM monitoring. If it was a bad sensor or reluctor ring it would be on all the time. The sensors all feedback back to the system their readings. There is a parameter window for the data. If any of the data goes out of the parameter window it will chuck up an error. When my front shocks were beyond help, everytime I went round a bend with an adverse camber it would throw a fault up.

Just skimmed this very quickly, but if it comes on after a while it is the cable, Porsche a repair cable for £100, takes 45 mins to fit. It resets every time you turn the car off and will only come on again when you turn the wheel and the wire internally break circuit again when it is looking for a signal, could be after 100m could be after 10 miles, but it will come on again. You need to know what side though, so read codes.

I’ve changed both rear and front sensors, I can honestly it’s the worst job I’ve ever done, an absolute PITA. Took about 3hrs each wheel. Maybe they just didn’t do it. They can be reset with a reader so when you pick up the car it looks like it’s fixed. It needs to be sorted as it’s an MOT failure.