VW Beetle Cabriolet Power Roof Incorrect Operation

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Steve Smith
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Joined: Sun Aug 25, 2013 7:22 am

VW Beetle Cabriolet Power Roof Incorrect Operation

Post by Steve Smith »

I hope this post will help someone out there when it comes to power roof operation as fitted to the the VW Beetle Cabriolet (2005 MY)

The vehicle in question suffered with a complaint of power roof inoperative.
The bottom line with this vehicle was the roof would attempt to raise off the front windscreen header rail but stalled in operation.
If the driver offered some manual assistance by pushing against the roof, it would start to open but again would stall. (The hydraulic pump continued to operate throughout)

Long story short, the manual hydraulic release valve located at the power hood hydraulic pump was not fully closed and so oil was allowed to "return to tank" rather than contribute pressure to the roof linkage rams.

Whilst this was an easy fix, I wanted to share the operation conditions of the roof when functioning correctly and whilst the release valve remained partially open.

Given the lack of product knowledge and in the interest of speed, rather than trying to locate the hydraulic pump fuse or wiring, battery support was applied to the vehicle battery with the ignition on but engine off.

A current clamp was then placed around the positive lead travelling to the fuse distribution board at the battery positive terminal and zeroed to discard any current flow to the various consumers drawing current with the vehicle in this condition.

Here we have adequate and stable current available at the battery flowing in one direction only. (Unlike with the engine running and alternator charging)

Once the roof switch is operated, any additional current flow is captured via the current clamp and only relevant to roof and window operation. Remember the current clamp was zeroed around the cable with ignition on engine off prior to roof operation.

The waveform below contains the battery voltage and current during the operation of the power roof from fully closed to open and latched.
After approximately a 2 second pause the roof was then closed from fully open and secured at the windscreen header rail.
Also included in the capture is a reference waveform (Magenta) highlighting the current drawn from the battery during leakage of the hydraulic release valve
Roof operation good and bad
Roof operation good and bad
We can clearly see the time differences between open and closure with the hydraulic release valve sealed and weeping
What really impresses me (I know I should get out more) is the detail available via current draw from the battery once all other consumers are zeroed out of view.

The operation of this roof requires the driver to release the locking handle in the roof where all 4 electric windows lower by a specific amount. (This is seen in the initial inrush current offending the trigger)

Next the power roof console switch is held to open the roof from the closed position where we can measure the full operation time and also capture the moment the roof is latched into position as both latching motors momentarily draw more current during their inrush stage.

After a 2 second pause the roof is closed from the open position where we see the latches release the roof and the roof travel to the closed position.

The final locking of the roof to the windscreen header rail is a manual process where the electric windows (that were automatically partially opened during "roof open" ) have to be manually closed via the electric window switches

This window close event is missing from the reference waveform (Magenta) as the roof required manual assistance to close and so exceeded the capture time.

The psdata file can be found below and I will add this to the waveform library.
Good power roof with bad reference waveform
(1.85 MiB) Downloaded 297 times
I hope this helps, take care........Steve

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