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Re: 164 Q4 ABS problem (warning light on)

PostPosted: Sun Feb 18, 2018 8:05 pm
by Alfan
I went for a short test drive in the Q4 yesterday and the ABS error code reappears after being erased. I will probably try and put the other unit back in later, to see what that will bring.

I took photos of the error codes from the Marelli tester.

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ABS error 1

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ABS error 2

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ABS error 3

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ABS error 4

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ABS error 5

Re: 164 Q4 ABS problem (warning light on)

PostPosted: Tue Feb 27, 2018 4:02 pm
by Alfamuppet
Looks like the front right and rear left solenoid valves have a problem ? These would be part of the ABS unit probably controlled by relays

Re: 164 Q4 ABS problem (warning light on)

PostPosted: Mon Mar 05, 2018 3:58 pm
by Alfan
As mentioned earlier, I have had the welded relays replaced - before that it gave *pump motor' failure. I think this is a problem within the mechanical unit, so I will try and replace that with another one and see what comes out of that.

Re: 164 Q4 ABS problem (warning light on)

PostPosted: Sun Sep 02, 2018 6:36 pm
by AlfaWhiz
Long time has passed but I will be posting an extensive update on the thread very soon.

I did a lot of measurements which will be helpful for everyone here (for example I've mapped all components from the schematics to the actual physical unit, so I know what is where exactly and how to measure it from the top).

At this point I'm pretty sure that my pump motor is shorted to ground thus causing issues on both relays, but I will ask you guys for your analysis here as well, so stay put, I'll post the details soon. :wink:

Re: 164 Q4 ABS problem (warning light on)

PostPosted: Fri Sep 07, 2018 12:32 pm
by AlfaWhiz
So here are the mappings I've done between the N51 group and schematic. You can see which diode is where in reality, diode labeled by me as 4 and 7 are not visible. There is also my crude hand drawing, where you actually can see what is connected to what, I will try to digitize it when I have time. :)




Hopefully this is helpful to everyone.

I'll be posting my measurements soon, as something does not add up in my case unfortunately. :mrgreen:

Re: 164 Q4 ABS problem (warning light on)

PostPosted: Fri Sep 07, 2018 1:09 pm
by AlfaWhiz
- I am measuring ground when the screw leading power to the pump motor is screwed down (this I suppose is short to ground, it's not supposed to be shorted, but I may be wrong)
- Because of this the measurements are split into 2: with the screw in place (would be normal operation, but I fear it's shorting to ground), and without the pump motor connected at all (no screw in place)
- After 10 or 15 seconds the solenoid valve relay disengages on it's own, I assume N51 group CPU is ordering it to shut off, this is measured as +10,8V on both pins 85 and 86
- I've marked in orange what I think is wrong on the measurements
- Battery voltage is measured at ca. 11.2V, drop to 10.8V on relays may be due to loss on the diodes
- I don't understand why the voltage on pin 87, 30 and 86 (as they are all connected) drops from ca. 10,8V to 0,7V when the relay is engaged (this is only on key ON)
- I don't understand why pin 30 of pump relay is getting 10,6V after 10-15 seconds when solenoid valve relay disengages, it should get it's current through pin 30 of said relay
- Even with the pump motor (and potential short to ground) disconnected, I don't understand why voltage on pin 87, 30 and 86 drops to 0,7V as it's taken directly from the battery via pin 87


Will be extremely grateful if anyone more experienced in electric circuits could help out here and diagnose why am I seeing what I am seeing here.

Many many thanks. :oops:

Re: 164 Q4 ABS problem (warning light on)

PostPosted: Wed Sep 12, 2018 2:06 pm
by AlfaWhiz
I was not expecting to say this, but... I FIXED IT :!: :!: :!: :!: :!:

Finally, after many years my ABS light is going off after initial checkup! I could not believe it when it first worked. :D

The diagnosis turned out to be somewhat misleading. What was ultimately the culprit was relatively straightforward: bad connection on the G416 60A main supply fuse for the ABS. :!:


What was misleading, was:
a) Diagnosis reporting error as "faulty solenoid valve relay" which was indeed not the case, but after one understands how this is verified (looking at the diagram you can see where the ECU takes it's inputs from)
b) No G416 fuse on the main ABS schematic, it's only included in the "hot wiring" section of the manuals
c) Loss of voltage only after the relay has been engaged

But nevertheless, it was suggested to me that I should check the supply voltage on pin 2 of G272 and go upstream from there, checking if it reads reduced voltage all the way. I had a look at the schematics to see where this wire leads to and ultimately found the "hot wiring" diagram, where G416 is mentioned.

The fuse (at least in Q4) is located right on the firewall, next to the coolant reservoir and next to the G56 junction (sort of screwed in and sticking out to the side of it). The two connectors holding the 60A fuse were completely covered in oxidation...

Cleaned it up and presto, ABS light goes off, voltage measures as it should everywhere!

ABS - solved. For the first time I have no warning lights on my dashboard! :mrgreen:





Re: 164 Q4 ABS problem (warning light on)

PostPosted: Thu Sep 13, 2018 9:59 am
by Alfan
Awesome!!! :D :D :D

I need to investigate this on my Q4, when I get time to start working on it again. Hopefully, it will have the same impact...

Re: 164 Q4 ABS problem (warning light on)

PostPosted: Thu Sep 13, 2018 12:01 pm
by alfa east
Wow, we all rejoice because you were on to this for quite a while!

Re: 164 Q4 ABS problem (warning light on)

PostPosted: Thu Sep 13, 2018 1:56 pm
by AlfaWhiz
It's tears of joy let me tell you. :D

I've just been testing the system with my Marelli tester, ran the pump motor test and the solenoid valve actuation test a couple of times to flush the old fluid out, and the system is blocking and releasing the wheels and pulsing as it should. Very satisfying :!: :)

Fingers crossed that you can sort out your issues as well, the main fuse should definitely be the first on the list.

Re: 164 Q4 ABS problem (warning light on)

PostPosted: Fri Sep 14, 2018 8:43 pm
by Alfamuppet
Great news and it’s brilliant when the fix is that simple!