W209 convertible roof issues

[crippo2]

Hi Guys

I have a 2008 A209 CLK convertible.

The roof is locked in the open position. Pushing the console switch down, drops the windows a bit and brings up both the 'roof in operation' and the yellow 'roof is doing something' symbol in the Instrument Cluster.

Previously I have had intermittent operation marked by codes B1928 (Limit switch 'INTERLOCKED' of soft top compartment cover remains in switched condition; Check switches S84/13 and S82/23: If they are good, then check the pump relay. I believe I have sorted by changing/adjusting relevant switches and relay) and B1942 (switch 84/3 remaining in switched position, which is a sign of the soft top not collapsing completely into its housing, thereby preventing a complete closure of the convertible roof, until the offending excess is pushed firmly into place)

I have put the car onto STAR, read and cleared B1942, then ran car for a bit, but still no roof movement or pump noise on attempts to close the roof.

On retesting, STAR tells me all is good and no roof related fault codes, whether from switches or relay actuations on attempts to close the roof.

All the micro switches are said to be in the correct position, the console switch works, the roof is seen as being locked in the down position.

I have theW209 Soft top Operation Diagnostic Aid, and it looks from that, that the pump and or 40amp fuse (both in left side of boot) may be the likely culprits. This is also confirmed by Klaus at Top Hydraulics in USA and on UTube.

Anyone have any other thoughts for investigation before I put the car into the tender (but expensive) hands of the Mercedes repair industry?

 

[Uncle Benz]

Have you checked that the gas struts that press the load compartment seperator are in good order, and are keeping the seperator pushed firmly into the microswitch? I’ve seen plenty where the folded roof touches the seperator and if the struts are weak it moves off the switch, preventing closing.

 

[crippo2]

Have you checked that the gas struts that press the load compartment seperator are in good order, and are keeping the seperator pushed firmly into the microswitch? I’ve seen plenty where the folded roof touches the seperator and if the struts are weak it moves off the switch, preventing closing.

Indeed I have. When not engaged by the separator and the console switch is depressed, the instrument panel display says words to the effect of 'close boot separator' When engaged by the separator, and the console switch is depressed, that message is substituted by 'roof in operation' (or something similar).
I will try to test the pump motor tomorrow by shorting the relevant relay pins together. If it runs then it may be the relay itself (was a 2nd hand purchase there are no new OEM parts either in UK or Germany!). I will also look at the 40a fuse, although if blown it indicates a pump motor issue (excessive current draw)

 

[crippo2]

Following on from yesterday's posts, today I looked into the relays, fuses and the pump.

All this is made more difficult because the roof is stuck down, but do-able.

Using WIS electrical document: pe7739-p-2102-99ba I was able to identify the main pump fuse (coming from prefuse F34 and situate in its own box adjacent to the pump. Opening the top and testing the battery power to chassis showed the fuse (40amp) to be fine, with the output voltage avaiable for the pump relays.

Next I removed the relays ( (A002 542 14 19) sitting immediately to the left of the pump and tested them for primary (energising) function and also for low resistance across the secondary (power) common and NO contacts. Both relays seemed fine (between 76 & 80 ohms for the relay coils, 165ma primary current and effectively zero resistance across the common and NO contacts once closed and when fed into an 8 ohm 20 watt resistor (say 1.6 amps).

Next check was to confirm that the relays had 12v power from the 40amp fuse to the relay sockets for NO connection.
finally I tested the resistance to chassis from the common contact in the relay sockets. This was infinite. Ah-ha. A quick check of the WIS wiring circuits will now reveal all.

Not so. The pump unit is a magic box marked A7/5 and, frankly is of no use for further circuit tracing.

Finally, having put it all back together, I tried the roof raise press on the console switch & F*** me the roof goes up as good as gold.

Perhaps all the disconnection/removing/cleaning etc before putting it all back has made a difference, but for the moment the roof is staying up whilst I travel to Le Mans for the Classic next weekend!

 

[00slk]

Sometimes that's all it is, dirty contacts somewhere in the vast miles of wiring

 

[crippo2]

Sometimes that's all it is, dirty contacts somewhere in the vast miles of wiring

I fear you might be right.
To check this our properly I will have to disconnect everything (including all relevant earth points), add a touch of Deoxit to everything and put it all back together.
The really really annoying thing is the fact that WIS, for all its uses fails absolutely to identify the insides of these magic boxes. Finding an apparant open circuit between pump motor input and chassis output is disconcerting and without any information, frustrating.
Still 3 good things:
1) I now know a lot more about the convertible roof than I did a few days ago
2) I am also a more effective user of STAR and understand actuations etc better
3) It was all free - no visits to MB for mega bucks of diagnostice and (possibly unnecessary) parts

 

[00slk]

I fear you might be right.
To check this our properly I will have to disconnect everything (including all relevant earth points), add a touch of Deoxit to everything and put it all back together.
The really really annoying thing is the fact that WIS, for all its uses fails absolutely to identify the insides of these magic boxes. Finding an apparant open circuit between pump motor input and chassis output is disconcerting and without any information, frustrating.
Still 3 good things:
1) I now know a lot more about the convertible roof than I did a few days ago
2) I am also a more effective user of STAR and understand actuations etc better
3) It was all free - no visits to MB for mega bucks of diagnostice and (possibly unnecessary) parts

Once you own or have owned old British automobiles you learn all about Lucas electrical and failing operations