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Posted (edited)

Thanks @Rick150. I feared this was the case...there appears to be a plastic cover under the chassis directly under the bolt. Do you know how to remove this cover at all?

 

Just a couple of extra questions if I may:

 

1) Do any sensitive electronic equipment need to be removed prior to welding (e g. ECU)?

2) What type of welding would suit this joint: MIG or ARC? (Bearing in mind I need someone to come to me instead of driving the car to a garage)

3) Can I just buy a normal M6 nut and weld it as a captive nut from under the vehicle or do I need to buy a special nut? Does the manual say what length the nut is?

4) Which wires terminate into this junction? Could it relate to my problem?

Edited by Willow5
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They are welded, need to grind it off from below, drill 8mm hole, fit the replacement by welding it underneath to the body. Stud should be M6, normally that would be 10mm socket for the nut. Tightenin

Check the high current connections, they are to thick ones from the battery under the seat to the starting circuit and to ground.   Now that you know it's a corrosion problem then unbolt and

You would be better served to run a voltage drop across each of the primary cables, none of them should drop more than 0.5V across their length after the connections are clean.  Any greater voltage dr

Posted Images

MIG welding is recommended.

I would buy a genuine stud but it's up to you.

 

Here is an option that will save you from welding but it has to be done right!

 

WWW.EBAY.COM

Find many great new & used options and get the best deals for 1x Ground Connector Tip Negative Earth Stud for Car Dent Repair Welding Machine at the best online prices at eBay! Free shipping for many products!

 

Remember that wiring corrodes on the Porsche because it has a galvanised body and when two dissimilar metals have a current path like moisture or even high humidity air the wires get eaten away. So, if you fit anything to a Porsche body make sure you use a paste to stop this action.

 

 

This is from the body repair instructions.

 

To protect electronic control units from over voltage during electric arc welding, the following work regulations must be observed:

  •   When performing welding work: Remove plug connections on the engine, transmission and airbag control units.

  •   Remove clamp from negative terminal of battery and cover the battery.

  •   When welding work is extensive, electronic control units in the immediate vicinity of the welding point

    must be removed.

  •   Connect the ground connection of the electric arc welding equipment as near as possible to the welding point on the part to be welded. Ensure that there are no electrically insulated parts between the ground connection and the welding point.

  •   Do not touch electronic control units or electric cables with the ground connection or the welding electrode.

Attached is what connects to MB26.

 

 

MB26.png

Edited by Rick150
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  • 2 weeks later...
Posted (edited)

Hi @Rick150. Well it seems that the original problem I had with the central locking has been resolved by re-doing various earth points around the car and in the boot. The strange thing though is that there is no audible warning when the alarm goes off and the motion detector detects movement inside the car (I tried this by having the window down then putting my arm inside once the car was alarmed). The only warning is the hazard lights flashing. 

 

That aside, I am left with 2 main problems:

 

1) starter motor is very slow to start the car, always starts on 2nd attempt not on 1st

2) I still cannot open the tailgate from the keyfob or the driver door button (but I can open the tailgate glass if I keep my finger pressed on the keyfob tailgate button for more than 2 seconds)

 

Do you know where the central locking module is located? Perhaps there is a fault with this unit?

 

Can you please let me know the exact locations of MB20, MB21, MB22, MB23, MB30 and MB31 please?

 

Other than this idea, I am now running out of options other than the engine bay area and the ground straps there....

 

Any other ideas?

 

 

Edited by Willow5
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Check the CCA of the starter battery, better still plug in a diagnostic unit that has the voltage curve when starting.

After starting the car put your hand on the terminals related to starting and if they are warm you have a bonding problem, can be + or -

Here is what you requested.

Grounds1.png

Grounds2.png

Overview.png

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Hi @Rick150, the CCA of the starter battery is 900A and the battery itself is brand new so I can eliminate any battery related issues. Unfortunately I don't have a diagnostic unit that can read the voltage curve when starting.

 

Where are the terminals you mentioned related to starting? Happy to put my hand on them but not sure if they are under the bonnet or near the battery fuses.

 

I forgot to say that I also have a 3rd fault which is:

 

3) Air Suspension Faulty Workshop error message appearing on the screen when I switch the car on

 

Is there any way of testing this ?

 

Today I will re-do the ground points in the roof (MB42 and MB43) and any others I can locate. Will report back later.

 

Thank you for all your help

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Battery connections to the starter is where you feel the heat.

Clear the suspension warning, in fact all warnings now you have fixed most of your problems and see if they re-appear.

 

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Posted (edited)

Sorry for the additional clarification but do you mean the connections near the battery (i.e. under the seat area) or under the bonnet please ? slightly confused :S

 

Will try to clear the warnings but have no diagnostic reader, will try to get hold of one and see what happens.....

 

Anyway, today I cleaned up MB42, MB43, MB20 and MB21. Nothing appeared to change from before so then I decided to pop the hood and looked at GP11, GP12 and GP14 and I must say that they looked visually awful with white surface corrosion to the terminals as they are directly under the windshield wiper cowl (not really sensible from a design point of view). I have yet to clear these terminals up and try again but in the meantime, please can you kindly let me know what is connected to these points?

 

Also, I tried looking for MB1 and MB5 but couldn't locate them at all - even after removing the headlight. Any ideas where I should be looking for these points? I think I have found a smoking gun 🙂

Edited by Willow5
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Check the high current connections, they are to thick ones from the battery under the seat to the starting circuit and to ground.

 

Now that you know it's a corrosion problem then unbolt and clean them, don't just look. Check any connectors you can get access to as well.

 

Grounds3.png

 

Grounds4.png

Edited by Rick150
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You would be better served to run a voltage drop across each of the primary cables, none of them should drop more than 0.5V across their length after the connections are clean.  Any greater voltage drop is a sign of corrosion inside the cable creating resistance and the voltage drop, which can only be corrected by replacing the cables.

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Thank you both. 

 

@Rick150, I will be cleaning them tomorrow because I simply couldn't get in the small opening with my drill attachment. Do you have any images that show what connects to GP11, 12, 13 and 14 in terms of wiring diagrams?

 

@JFP in PA, good idea. Which wires should I test? There are an awful lot of them. Also do you know where the negative ground strap to the starter motor is physically routed inside the engine bay so I can feel for any heat?

 

Thanks both, this is a lengthy process but hopefully will pay off soon

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9 minutes ago, Willow5 said:

Thank you both. 

 

@Rick150, I will be cleaning them tomorrow because I simply couldn't get in the small opening with my drill attachment. Do you have any images that show what connects to GP11, 12, 13 and 14 in terms of wiring diagrams?

 

@JFP in PA, good idea. Which wires should I test? There are an awful lot of them. Also do you know where the negative ground strap to the starter motor is physically routed inside the engine bay so I can feel for any heat?

 

Thanks both, this is a lengthy process but hopefully will pay off soon

 

The wires you need to test are the primary cables, the large battery cables.

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Hi @Rick150 and @JFP in PA. Please can one of you kindly point out where MB23 is located? I see from the diagrams that it is the left side of the dash but what I don't quite know is whether it is buried under the footwell carpet or whether it is actually somewhere to the left of the centre console? 

 

The reason I think it is important to trace is because it is linked indirectly to the rear comfort systems module via the signal horn and this is one connection I haven't addressed.

 

On another note, I tried cleaning the joints under the wiper arm cowls but this has not has the desired effect. I have yet to test a volt drop over the cables so that will be my next option.

 

Finally, please can you kindly advise where the rear comfort systems module is physically located? 

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Posted (edited)

Hi @Rick150, hope you are keeping well during these times.

 

Can you please dig out thr wiring diagram for the interior tailgate release button as I think I am getting close to resolving this issue but need to identify where this button routes. In the past you send me some diagrams but nothing with the interior tailgate release button so far.

 

Just out of interest, I read somewhere that this button is disabled if the cayenne thinks it has a towbar fitted. Question is how do I disable a towbar if the cayenne thinks it is installed? Can't see anything visually near the rear bumper but I am no expert on the settings yet. Thank you

Edited by Willow5
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Just to put my mine at rest did you check fuse 31? when you try and open the tailgate it will make noise but not open if 31 is blown. It's under the left side dash cover.

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Posted (edited)

Hi @Rick150, no need to check the fuse as the tailgate opens and closes perfectly when I use the handle at the rear.

 

Please can you kindly send me all the wiring diagrams for the interior lights circuits as that is where the switch for the tailgate release is located.

 

I have this diagram but it makes no sense to me as both the fuel flap and tailgate lid switches are connected to the same wires. Can you explain it at all as I am baffled by it. 

 

Also I have 4 wires going into my tailgate switch, not 2. The other 2 are VIO/WHI and Brown which are not shown here....this is a complete mystery to me

 

 

 

Screenshot_20200330-112021_Drive.jpg

Edited by Willow5
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The wiring for the lights is quite extensive and quite difficult to put into a format to post. I recommend going to eBay and purchasing a manual.  Not all models comply with the wiring diagrams I have as they are mostly for the 957 although 955 is pretty much the same.

 

This shows the lock and light combination.

Rear Interior lights.png

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Thank you @Rick150. Is there a diagram similar to the one I posted above that shows the "tailgate switch" and the "tank cover unlocking switch" which routes into the "driver door control unit". I am only interested in this now as those controls are on the drivers door and that is where the problem is

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There is no direct wiring from the drivers door to the tailgate, it goes to the Driver identification control unit that decides if all the conditions are met to open or close it then passes it on. As you can see from the circuits of the Tailgate that it all terminates to the CAN BUS which talks to the control unit. Could be that one of the conditions to activate is not true, which one I have no idea.

 

The Cayenne has an electrical system that relies on LOGIC that's present on the CAN lines and in the control unit there will be a 'Truth Table' that decides if to let you activate anything. If you had a scanner it might point to what seems like an unrelated fault code that could help.

 

 

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