Help! F355 ABS Gremlins (one for the electrical gurus)

This assumes the ECU is providing power, but not enough to light a lamp, right? Thanks I'll go and try all of the above now.

Fuses are fine. That was the first thing I checked. Fingers crossed.

 

OK so it lights a lamp no problem. Tried tapping it, no go. Not a sound.

I havent actually fed it live power yet, but that's a bit tough for me as I don't have a reliable 12vdc power source for it...

 

OMG.......

OK so I hunted through my old batch of electronics testing gear and found and old DC power supply. One of those bench units that can provide between 0-30v and 0-30a of power.

Connected up some cable to it, set it to 12.6v unlimited load (so 30A max).

Connected the wires to the pump.

And it ran.

The jumper on the car side measures voltage and enough curent to light a side indicator bulb.

I tried reseating half a dozen times, no joy..... I might just be dealing with a bad connector here fellas.

@m.stojanovic are you sure if it lights a bulb it's supplying enough feed? The relays are definately triggering, when I pull the ABS pump power relay out I can hear it click and the 12v to the pump dies.....

Surely not just a connector.

Pump pressure is definitely coming up because I'm getting a softer pedal as it primes.

 

Yes, same location but a totally different setup.

 

I'm going to put some more load on it. I used an indicator bulb, I'll try a headlight bulb. The indicator bulb is only 0.4a (5w) whereas the headlight bulb is 65w (5 amps).

 

Oh boy, oh boy....

OK here we go fellas...

12v from the car. It won't run the pump, but it lights a side indicator bulb (5w). So I assumed power from the car was OK.

Connected this to the pump. no go.

Put 12vDC manually into the pump. It ran.

So a bad connector I'm thinking... Cleaned the connector. Was that it?

No.

Put a 65w high beam headlight into the same output from the car. Nothing. @m.stojanovic was spot on. It was ECU power I was seeing, not 30a from the relay.

All relays click when inserted as they should....

So here we go.... Ready?

Pulled the one relay I couldn't get out before (the green one below). Reseated it. Turn on ACC, pump ran and all error warning lights went OUT.

This is what the mechanic did last week, thinking that the clean fixed it - when in fact it was a reseat that fixed it. Why would a re-seat fix a relay?... Wiggling it didn't help, it had to be pulled and re-seated.

Who knows, but tell me this guys - do these relays look OEM to you? Has somebody put the wrong ones in sometime during its history?

I'm gonna kill this car. But we're getting _really_ close now!

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Black one is ATE, green is Siemens, yellow is hella. I’ll check more closely tomorrow. The sockets all look the same so who knows maybe they were put back in the wrong way?

I might just order a new set of genuine ones to be sure and will squeeze down on all spade connectors with my crimp tool.

I’d rather be sure and not have to pull the damn carpet liner out again! That’s getting real old...

 

Nope. Once I reseated that relay, the pump came on and both the ABS and brake warning lights went out. Pedal went softer as it should, 6 pumps and the pump came back on - so accumulator also ok.

 

I concur it's highly likely however with all of this, if there's one thing I've learned and that's never to say the word obvious

The blown diode I think accounts for the years of issues with the ABS light that the previous owner had. The pump failure, brake light and ABS light is something completely unrelated and co-incidental I think.

I'll take a look at all the spade connectors and may actually go to the effort of replacing them. I'll also follow the power supply chain for that pump further up and ensure all the upstream connectors are also cleaned. The fact that particular circuit is relatively simple should hopefully make it easier to pinpoint.

 

OK guys I have a resolution.

First a super shout-out to @m.stojanovic for all his help. After a heap of diagnosis we've finally figured it out.

For future generations and googler's out there, here is what fixed it... But first, a bit of a diagnostic path to help explain what was going on.

So the black pump relay was clicking when being inserted into its holder, but the pump was not activating. I removed the pump power lead and tested voltage, 12.6v. This has me stumped until we then figured out it was delivering 12v, but not enough current. How did we know this? It could light a 5w bulb but not a 65w bulb. Genius test huh!

So after a bit of mucking around with the other relays to determine they were OK, attention then turned back to the black pump relay.

I took the relay out to bench test it. Connected 12v to the switch circuit, and it activated just fine (click click click) when supplied 12v.

Next logical step was to test resistance on the load circuit in the relay. When the relay was open, it measured infinite resistance. When closed, 0 resistance (Ok well 0.001). So logic would dictate the relay is fine, right?..... OK well this is where the story gets interesting.

Before I started pulling the wiring loom apart to clean up the spade connectors on the underside of the relay's socket, I thought I'd just humour myself and do a couple more tests.

First I removed the power connector to the pump and verified there was still 12v to the pump. Yep, still has power. Enough to run a 5w bulb, but as before, not enough to run a 65w bulb.

Interesting.

The next obvious step is to pull apart the spade connectors on the socket right? Ugh what a ball ache... Before I did that I thought to myself screw it, I'm just going to jumper the socket manually. Bridge the load circuit like the relay would.

So I put a test wire across the load circuit on the relay's socket, and BAM the pump came up... A fluke in the connector perhaps? No. Each and ever time I tried in a multitude of different points on the connector's spade connection - it came up. No lose connection there.

So this is where my brain go into a while(1) loop (you programmers will know what I mean)…. Que? This makes no sense.

On one hand there's a relay that opens/closes on command and measures no resistance on the load circuit once closed - YET it doesn't work when inserted and everything runs 100% when you use a simple jumper wire on the socket.

At this point I'm working on a theory that the relay can test zero resistance on the multimeter BECAUSE there's next to no load going through it. Once significant load is introduced (ie pump load), I'm theorising, resistance goes up.

Co-incidentally, after all my testing I've noticed this relay is getting DAMNED hot.

So although I'm convinced it's the relay I'd love to be able to conclusively prove it... That's just how my mind works I'm afraid.

I break open the relay and look inside. Like most relays it's fairly simple. I locate the switch (circled below) and gently file it with a small automotive file.

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Back in car. Turn on the key and BAM it works straight way. Pump the brakes, it comes back on again after about 6 pumps.... Keep trying, all good.. Key out, pump all the pressure out - key back on and on she comes.... All dash lights out, all good

The internal contacts of the relay that bridge the load were obviously oxidised or whatever. The light filing fixed it up. Issue is 100% fixed. The relay is now only slightly warm as opposed to hot.

Just in case anybody wants to know, @m.stojanovic is the man.