[928uk] ABS Relay failures

Sat Jun 8 16:46:17 UTC 2024

The failure mode of 928 ABS relays that I have observed is one of the coil wires coming away from its connection point internally.

Unfortunately, repair is very difficult because access to the connection point is blocked by a solid metal connection strip, and disassembly of the relay is prevented by the plastic moulded base that seems to have been moulded around the contacts at a late stage in the manufacturing process. Because these relays often fail, and can't be easily repaired, even used replacements are expensive to buy.

As Smiffy mentioned, they are special in that they contain a Zener diode, and it's not just any Zener diode it's a high power one on a big metal heatsink. The Porsche electrics designers obviously expected that Zener to have to work hard for its money.

The long and short of this is:
               a) get hold of a spare ABS relay any time you see one at a reasonable price, or consider buying a new one from Porsche before the price goes up even more!
               b) I would welcome receiving any failed ABS relays in order to investigate the issues further, with a view to one day either finding a cost-effective way to repair them, or creating a new replacement relay. So if you plan to bin an old failed 928 ABS relay please get in touch with me.

BTW, for those that aren't aware, I can repair faulty S4/GT/GTS headlight double relays (actually 4 relays in a double case) because I painstakingly worked out the control circuitry inside them. The brand new replacement Porsche headlight relays (928 618 107 63  & 928 618 107 64) had a poorly specified component in them, which caused issues for some 928 owners in the past. I wrote a report on the problem and sent it to Porsche, but whether they have fixed them now is anyone's guess.

Best regards,
Jonathan

1991 928 GT Amethyst Metallic

-----Original Message-----
From: 928uk <928uk-bounces at lists.928.org.uk> On Behalf Of Donald Peach via 928uk
Sent: 07 June 2024 16:55
To: 928uk at lists.928.org.uk
Subject: Re: [928uk] ABS Relay

Many thanks, Smiffy and Vince. The same fault occured on mine last year, 
but on bench testing the relay, it functioned and the fault didn't occur 
again after placing it back on the car.

I have just phoned the OPC and they quoted £86.36 with delivery for 
Tuesday, so as you say, Smiffy, with 10% discount, worth buying new. 
With confirmed availability and delivery, I have now broken into the 
relay housing and it is indeed not closing with 12v feed.

This has all happened with just one week until MoT due, but I would 
rather not try and fool the tester, as I have good rapport with them and 
the 928.

Many thanks for your advice.

Regards,

Don.

On 07/06/2024 16:22, Paul R Smith via 928uk wrote:
> 03 is the correct replacement, at £86.83 list price (you should be 
> able to get 10% off for club membership at the OPC).
>
> It's just a normal relay but with a Zener diode and heat sink added, 
> presumably because the ABS solenoids generate lots of voltage spike 
> when they operate. If you want to save money you can connect in a 
> socket for a standard relay, leaving the existing relay containing the 
> Zener diode. A second hand one would need to be significantly cheaper 
> than the new one to be worth the risk that it will go soon.
>
> On 07/06/2024 16:08, Donald Peach via 928uk wrote:
>> Hi.
>>
>> I have an ABS warning and before I jump in and possibly create more 
>> problems I thought I would ask for help. My ABS light is on from key 
>> in ignition and doesn't go out on start up. I believe that this 
>> indicates a relay fault; on bench test I have connected a 12v supply 
>> and it is not switching in and out.
>>
>> I haven't been able to pull the cover off - it would need 
>> considerable force or manipulation, so I am looking at a replacement. 
>> Part No. 928 615 124 01. There are several secondhand relays on offer 
>> at £50+, and I can't find new, except with 928 615 124 03 (Ci. 
>> £80.00). Has anyone had a similar issue and can say that this an 
>> acceptable replacement, please?
>>
>> The date on my relay is original for the car, 22.01.88.
>>
>> Many thanks,
>>
>> Don.
>>
>> 1988, Manual S4.
>>