W124 Cab Roof Problems

[Andy_C]

The roof on my W124 Cab has stopped working correctly: the soft top cover will not go down.

The hydraulic reservoir is full , all operations done with the engine running, fuses checked.

The roof will retract normally until the point where the soft top cover should shut. It then ceases to function. At this point there are no faults on the diagnostic port ( read with a blink reader). If I reverse the process, the roof will shut correctly ( including the soft top cover shutting ). Still no faults on the diagnostic port. If I manually intervene and close the cover by hand, it will lock in place, but the roll over bar won't raise. I then get fault code 8 ( soft top bow locked switch s84/8)
The solenoids on the valves measure the correct resistance (5 to 15 ohms) and have power going to them at the right time in the roof movement sequence. I have measured the action of all the switches: they all change from low ohms to open circuit when they should. I am having difficulty measuring a voltage going to the switches as the plug to the soft top controller (124 820 4526) precludes me from measuring there and I can't gain access to all of the switch terminals. However, as the resistance on the switches change when they move, I'm pretty sure the switches won't be at fault and if I can measure power to solenoids Y56, Y5 and Y4 at the correct time in the sequence the controller should be working.

Any help/advice gratefully accepted.

Andy

 

[Scott_F]

Have you checked all of the fuses ? There are at least two for the roof mechanism on a W124 and one of them is not in the main fuse box.

 

[Andy_C]

All 6 fuses checked and are working.

Thanks,
Andy

 

[WDB124066]

It does sound like the controller is not receiving a signal to say that the hood is fully retracted into its well, or that the signal it is sending isn't being received by the hydraulics to close the lid.
Is there a code reading port for the hood & rollbar that is separate from the engine e.t.c. code port...?

 

[boomtings]

It does sound like the controller is not receiving a signal to say that the hood is fully retracted into its well, or that the signal it is sending isn't being received by the hydraulics to close the lid.
Is there a code reading port for the hood & rollbar that is separate from the engine e.t.c. code port...?

under the passenger footwell is a seperate roof 2 pin test connector for the roof (you need to supply your own 12v for the tester)

it does sound like the controller is not getting the correct signal.

OP: if your in London your welcome to try swapping controllers with me.

 

[Andy_C]

Thanks for the reply. That was the position I was using to measure the codes.

Andy

 

[WDB124066]

You'd have to be thinking of checking the micro that sends the signal to the controller to tell it the soft top cover is ready to lower - the bow is stowed, or the one that activates the hydraulic rams for the cover.
You have tried the main OBD codes too, and nothing shows at all - anywhere...??

Try resetting the roll bar by pressing the down button for a good 30 seconds or more until it lets you know it has mechanically reset itself...??

Apart from that it may well be try another unit.

 

[WDB124066]

Top center in front of the master cylinder are some fuse boxes in black - including a big strip fuse... All good?

 

[WDB124066]

This may help....

 

[Andy_C]

Thanks for the reply. All fuses are good. If I remove one of the fuses associated with the roof, the sequence doesn't even start. I've measured ( to the best of my ability) all of the microswitches: when I move them, they change state. There is power going to the valves ( measured at Plug X on the controller). I can only conclude that my controller is playing up.

Regards,
Andy

 

[Andy_C]

Thanks for the codes: those are the ones I've been reading. I get no codes ( apart from 1: no fault) until I manually make the soft top cover: I get them fault code 8 but have put this down to the fact that I'm manually doing this operation.

Regards,
Andy

 

[WDB124066]

Well code 8 would make sense. Here is its location - easy to get at too.

 

[Andy_C]

All the switches are easy to get to at the moment. The car is in it's component parts!
The switch illustrated makes and breaks, exactly as you'd expect it to: when closed it measures 5 ohms, when open it measures open circuit: the hydraulics cause it to change state when it should as part of the roof opening sequence.

Regards,
Andy

 

[WDB124066]

Well, is it a matter of changing the controller then...?

 

[WDB124066]

A dry solder joint in the control unit where the wires connect or a breakdown in insulation/conductivity [e.g. corroded plug/s] on the wire/s to from the micro 84/8...? But then you arranged for that fault manually... So maybe take a good look at the hood bow ones instead..?

 

[Dee-124CAB]

Probably the most uneducated suggestion of the lot..... but if the car has been in hibernation over the winter, make sure the battery has enough juice to power the whole roof mechanism in its entirety as it does require a fair old bit of power from the battery and as you been putting the roof through its paces it could be a little flat..... sometimes its the simplest things...

Best of luck..

 

[Andy_C]

Thanks, but I've been investigating with the engine running. Cost me a fortune so far!

 

[bolide]

I had an interesting fault with one of those flat fuses. MB used them for additional factory kit like the heater fan on a climate control car

The fuse had split but the two halves were still making contact. I got 9 volts at the fan which started me thinking. Because the contact between the two halves was poor, it was high-resistance and, despite there being volts present, the fuse would not pass any current so the fan would not work

Worth a look!

Nick Froome

 

[WDB124066]

Yep, I've had that too!

 

[boomtings]

Andy came over this evening and we tested his roof controller. We found that his controller is bad and my car had the same symptoms as his.

Interestingly it nearly worked the first time but then froze while the windows went up. After that it would fold the roof back but the lid would not shut.

Sorry Andy , I forgot to offer you a cup of tea or a bite to eat.