[928uk] ABS Relay failures

[Paul R Smith]

The reasons I chose the "piggy-back" option were:
There was an empty space next to the ABS relay position on my CEL.
If the relay fails again, it's a simple matter to plug another standard 
relay in.

It's really what Porsche should have done in the first place, i.e. had a 
Zener diode (and heatsink) in one position and the relay in another 
position.

Smiffy

On 08/06/2024 17:46, jonathanrackowe--- via 928uk wrote:
> 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.
>>>