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PLEASE HELP - Golf 4 electronics [video]


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#1 metalc4mp

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Posted 26 September 2020 - 08:38 AM

Hi, I have a problem with my Mk4 --> when I press both brake and clutch pedals, the electricity supply lowers down.

 

By that I mean that for the time of pressing both pedals, the headlight, taillights, interior and dashboard lights all get dimmed, radio shuts down and I get ABS and battery lights on the dash for a second or two.

VIDEO: https://www.youtube....h?v=z6y_SjabkVQ

 

VCDS shows plenty of errors, but the fault solutions all point to common things (fuses, wiring or battery/generator) so it should be a common source.LOG: https://pastebin.com/WMkSrmp4

 

The fuses are fine, battery is charging when I measured, what else can I look into?

 

Help please!




#2 ttg4l

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Posted 26 September 2020 - 09:13 AM

Maybe a bad battery? Does it crank over slowly when you try and start it after it's sat overnight?

#3 Gti Fly

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Posted 26 September 2020 - 09:29 AM

You must have a problem with the wiring somewhere .

Seeing as it happens when you press those pedals, have you had a good up close look at the wiring above the pedal box ?

So underneath the steering wheel dash plastics, remove the lower dash plastics and inspect the electric power rail.

There's earth. 75x and 30. It's a row of power junctions. Check all is nice and tight , nothing loose or shorting .

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#4 metalc4mp

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Posted 26 September 2020 - 10:33 AM

@ttg4l It doesn't crank slowly, the battery is keeping a steady voltage while the engine is running and is being charged when you press the gas.

 

@Gti Fly Interesting, so a loose wiring can cause such loss of electrical current for the whole car?



#5 Gti Fly

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Posted 26 September 2020 - 11:40 AM

It's certainly worth checking as everything above the pedals is electrical.

And it seems to be pedal related.
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#6 adam-

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Posted 26 September 2020 - 08:02 PM

Do the revs drop?


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#7 metalc4mp

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Posted 28 September 2020 - 04:50 PM

@Gti Fly I checked everything I could reach underneath the dash...was all fine and tight.

 

@adam No, the revs are fine, but in the video below they drop because I pressed the clutch and stepped off the gas, because that's how I can turn the fault lights on.

 

Video: https://www.youtube....h?v=z6y_SjabkVQ



#8 ttg4l

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Posted 28 September 2020 - 04:56 PM

Just to clarify, it doesn't do it when you press only the clutch down and let the revs fall to idle, right?



#9 metalc4mp

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Posted 29 September 2020 - 02:19 PM

@ttg4l That is true.

 

I have an update: it has been 3 days without any major rain and there was zero problems with the car. I'm expecting them when the cold starts or some storm catches me while driving.



#10 ttg4l

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Posted 29 September 2020 - 05:46 PM

Take a look at the ECU wiring by the wiper linkage, the linkage can rub through the sleeving and only cause you an issue when the wiring gets wet.



#11 metalc4mp

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Posted 29 September 2020 - 06:11 PM

Before I open anything up I'd kindly ask you to confirm my understanding, you're talking about this clump of wires:

uhs4Uog.jpg



#12 ttg4l

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Posted 29 September 2020 - 06:35 PM

Nope, not that. Further over, there's this.

 

The wiring runs left and right, wherever it runs by the wiper linkage it can rub.



#13 Gti Fly

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Posted 29 September 2020 - 07:41 PM

Have u checked the condition of the main earth cable under the battery tray ?

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#14 GTMonster

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Posted 29 September 2020 - 10:38 PM

Random thought... How about the brake pedal switch located above the pedal. From recollection, it's removable below the steering wheel column in the dash.

I replaced mine a few years back after it failed. Got warning light in the dash and cruise control wouldn't activate.

There are 4 wires terminating into the switch for brake lights and connection to the onboard computer. Check these wires around the pedals for shorts. I don't remember if they pass near the clutch pedal, but I'd check around there in case.

If the radio is off, do you get the same issue?

Can you smell any electronics burning smells when it happens?

Possible alternator issue. Is the alternator turning smoothly and outputting power correctly? Do you get the same issue with only the ignition on, but the engine off?

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#15 GTMonster

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Posted 29 September 2020 - 10:45 PM

Also check for shorts in the brake light wiring and high level brake light wiring around the rubber boot between the body of the car and the boot door. That said, these should cause yh supplying fuse to rupture unless the wrong fuse has been inserted in which case the wiring would not be protected.



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#16 metalc4mp

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Posted 30 September 2020 - 06:36 PM

@ttg4l Alright thanks, I will look into that.

@Gti Fly Main earth cable looked fine, no rust or dirt present.

@GTMonster I have dis and reconnected both brake and clutch switches, VCDS shows them responding correctly (logical 0 or 1).

There are no burning smells present.

Regarding the alternator, I can't really tell you as I'm not that familiar the device, I only know that the battery is keeping a steady voltage while the engine is running and is being charged when you press the gas.



#17 adam-

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Posted 01 October 2020 - 07:24 AM

The switches wouldn't draw enough power to literally cause so much current draw the lights dim, you'd have melted something by now.

 

Does the battery voltage stay high (+14) when you do this?  If you're able to hold the revs up?  Use your left foot to clutch and your right foot to heel & toe (brake and hold the throttle).  With the revs up, does this happen?  Potentially the ECU isn't commanding a load increase from the alternator - remember it's got an excite wire and an ECU load reference.


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#18 GTMonster

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Posted 01 October 2020 - 11:28 AM

When you're engine is running, you will be reading the alternator voltage which will also be charging the battery. This is usually a couple of volts higher than the battery voltage. The alternator charges the battery to start the car and also powers the electrics in the car when the engine is running.

You appear to be describing volt drop/sag due to too much current being drawn from the cars power systems. Or that the power systems are not producing the required power to sustain the load.

What I can't understand is why when pressing both pedals... A short in any circuits around there or for that fact in the car should rupture fuses due to drawing too much current through them. Also to prevent any damage to the wiring.

I can't think of any other areas of the car where the clutch and break interface to cause this kind of issue.

Did you say that you have tested battery voltage without the car running? Have you watched the battery voltage when pressing the pedals in this state?

What happens when you turn the ignition and stereo on (engine off) and press the pedals?

How old is the battery?

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#19 GTMonster

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Posted 01 October 2020 - 11:38 AM

Have you tested the voltage at the battery while revving the engine with nothing else switched on in the car? It should be steady around 14ish volts. If it is varying wildly with revs, then the regulator on the alternator is playing up.

If your meter has peek voltage hold, see what the peek is when revving?

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#20 northpole

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Posted 01 October 2020 - 11:46 AM

I would start with removing the battery and cleaning all the earth points on the car than put it back... if that doesn't help than i would suspect the alternators circuitry at fault especially if you haven't burned any fuses...  



#21 GTMonster

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Posted 01 October 2020 - 11:47 AM

Have you tested the voltage at the battery while revving the engine with nothing else switched on in the car? If it is varying wildly with revs, then the regulator on the alternator is playing up.

Do the same with all lights on full, fan, A/C etc and stereo pumping. What does the voltage get down to?
It should be steady around 14ish volts with no load with a slight drop with everything on under load.


If your meter has peek voltage hold, see what the peek is when revving?

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#22 GTMonster

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Posted 01 October 2020 - 11:49 AM

Sorry I was editing my last message, but appear to have started a new one.

Agreed, clean the battery terminals first to ensure correct conductivity.

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#23 GTMonster

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Posted 01 October 2020 - 11:55 AM

One thing.... Is your serpentine belt running correctly?Any slippage, when A/C and significant electrical power is being drawn?

Also is your AC pump/ pump clitch running correctly as this could be stopping the serpentine belt.

Also check the belt tensioner as this can lock up.

The serpentine belt powers the alternator. So looking around there could also be helpful.

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#24 Gti Fly

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Posted 01 October 2020 - 03:10 PM

The thing is, the problems seem to stem only when he presses the pedals , even at stationary. So don't you think it's likely to be with something around the pedal box area causing the issues ?

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#25 GTMonster

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Posted 01 October 2020 - 06:06 PM

I don't think anyone is ruling that out, but what in this area draws enough current to cause volt drop/sag of this level without rupturing a fuse.

The dash panel displays engine warning light which can even mean anything from a brake switch fault (tested OK) to a load of other things... then the battery light would appear to indicate under voltage as it coincides with power loss.

Brake lights draw circa 3.5amps assuming 21W each @ 12V. Alternator drops to idle speed when clutch pressed so power output drips off. Possible thought that the alternator regulator isn't functioning correctly / calling for more power from the engine.

That's where my weird brain takes me.

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#26 adam-

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Posted 02 October 2020 - 07:46 AM

I don't think anyone is ruling that out, but what in this area draws enough current to cause volt drop/sag of this level without rupturing a fuse.

 

Nothing does - hence my suggestion...


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#27 GTMonster

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Posted 02 October 2020 - 10:05 AM

Nothing does - hence my suggestion...

I was responding to the previous post regarding the pedal box.

I'm very much with either battery failing or alternator issues. Possibly both.

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#28 metalc4mp

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Posted 05 October 2020 - 01:58 PM

OP here

@ttg4l I checked the wiring by the wiper linkage, seemed alright to me. Pics: https://i.imgur.com/6lC0HmF.jpg https://i.imgur.com/c2lGnLN.jpg

 

I can't answer all the battery voltage questions because I don't have a multimeter BUT I did replace the battery and the problem persists.

 

@northpole I did clean the earth points, although they didn't need much work.

@GTIMonster The belt tensioner was replaced a few months ago, regarding the serpentine belt itself I can't really tell by myself.

@Gti Fly While it is true that pressing the pedals triggered the dash lights, it only did when there was severe rain outside.

 

 

During this time there has been 5 days of dry weather and zero problems with the car. On the 6th day a bad storm came and while I was driving and all of the sudden the ABS light came on and off once.

I was curious so I slowed down and pressed the clutch and the break and the ABS + brake fluid lights came on and off (yellow). I repeated this 3-4 times until the both lights stayed on with beeping.

Next thing - I stopped the car and turned it off. The first ignition attempt light up the dash for a second, then shut off as there was not enough power to even spin the starter. The second ignition was just fine, no light since then.

 

Ideas? (crying)



#29 Imagewerx

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Posted 05 October 2020 - 09:27 PM

I think you need to measure for actual quantifiable voltage drops otherwise you're running round in circles here.Measure across the battery and at the terminals on the base of the relay rack.The battery should be just over 14 volts at engine idle,inside the car about 0.1 volts less and no more.



#30 metalc4mp

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Posted 06 October 2020 - 02:39 PM

>> UPDATE <<

Alright I bought a multimeter today and measured what you guys recommended. These were your voltage measuring suggestions:

 

▶ Car off voltage: 12,6 V

▶ Idle running battery voltage: 14,2 V

▶ Holding 2500 rpm voltage: 14,44 V

▶ Idle running + full fan A/C, stereo, long ligts etc. on: 14,28 V

▶ Idle running + pressing clutch, brake: 14,25

 

Please note: It was a dry day and my dash wasn't acting up if I pressed the clutch, brake nor did any of the lights dim. I will try this once more when it occurs again.

The voltage was not stable while measuring. I tried measuring another MK4 and holding at 2500 rpm showed me steady 14,3V while this one was all over the place bewteen 13 and 14,5 volts.

Should I try switching the alternators between the MK4's or is it the alternator's fault? 

 

adam- 

The switches wouldn't draw enough power to literally cause so much current draw the lights dim, you'd have melted something by now.

 

Does the battery voltage stay high (+14) when you do this?  If you're able to hold the revs up?  Use your left foot to clutch and your right foot to heel & toe (brake and hold the throttle).  With the revs up, does this happen? 

Also tried this, voltage stays high (varying around 14 as mentioned above).







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