Audi A4 Cabriolet - Roof warning light flashing 10x

[whiffin]

I have a 2006 A4 3.2 FSI Quattro S-line. - B7.

Anyway, the roof works perfectly. But when I turn the engine on I get 10 flashes of the warning light.

Originally I had these errors via a generic handheld device:

02000 - Switch position inplausible
01986 - Convertible top frame position sensor (G356) - electrical fault in circuit
00532 - Supply voltage B+ lower limit exceeded
(top frame poition for G356 was 237)

I had it reset, and then it worked for a few weeks, then it came back and I had the following (via VCDS)

02000 - Switch position - 008 - implausible signal - intermittent
01986 - Convertible top frame position sensor (G356) - 012 electrical fault in circuit
01988 - Convertible top operation switch (E137); Close 012 - electrical fault in circuit - intermittent

So yesterday I had reset via VCDS again, did a manual reset as well.

Tried the roof a few times - perfect.

Then it's come back again! with with just this warning

01986 - Convertible top frame position sensor (G356) - 012 electrical fault in circuit

The G356 sensor looks OK, the whole roof looks in good condition, and it all works.

Ideas?

Thanks

[whiffin]

SOLVED (I think):

As above the sensor in question was G356 (error code 01986), but as roof was working I assumed sensor couldn't be completely shot. Linked to VCDS and looked under section 26 (auto roof), cleared code, then plotted real time graph of output from G356. It went down lots, slightly up, then down (as it should) but didn't look smooth, and every cycle or so it spiked down to 0.

So I figured that as it's a variable resistor that doesn't get used much, and only moves a little, it could be dirty tracks giving bad connection.

So took it off (1 screw & 1 connector so 30 seconds), it felt a little rough, so squirted wd40 in the gap, and wiggled end to end about 200 times. Much smoother.

Reassembled, manually reset roof. And opened VCDS again.

Graph for G356 when roof opening and closing is perfectly smooth, with no spikes up or down.

Done 10 cycles so far, no error code.

Fingers crossed