500 SL Alarm............or not?

[stats007]

To be honest you may be better off going to a friendly independent who will do this for you for beer money. I'd at least speak with the chap who sold you the car or last serviced it.

If you're competent with electronics then you can retrieve the codes yourself by grounding the LED to the socket you want to get codes from:

 

[Hartzpartz]

Thanks for that stats007. My diagnostics socket appears to be of a square design (4 holes in a square formation next to a load of others).

Perhaps this was the fore runner to the round socket?

 

[stats007]

There are different diagnostic sockets on the car - do you mean the 16 pin connector? There is a further 4-pin connector in the passenger footwell purely for the soft-top and roll-bar.

 

[Hartzpartz]

This is what I mean..................under the bonnet on the near side.............

http://i179.photobucket.com/albums/w304/Hartzhorne/SLDiagnosticSocket.jpg

 

[stats007]

Yep - that's the 16-pin diagnostic socket:

 

[Hartzpartz]

I knew you'd have the right diagram!

Thanks again to stats007! Where do you get all this stuff from? Do you have the WIS thingy?

 

[stats007]

I used to have WIS but most of the info I've collected comes from various forums etc. The US is a good source but their cars differ slightly.

 

[Hartzpartz]

It's been a while but I finally got round to making the "code reader" (see previous wiring diagram supplied by stats007).

When I connect the black earth wire to pin 1 of the diagnostics socket and the red wire to pin 16, the LED illumintaes when the ignition is switched on.

If I operate the momentary switch, the LED goes out and comes back on again when I release the switch button.

So far, so good.

When I connect the yellow wire to the circuit to be checked (i.e pin 6 - SRS system) what should happen?

At the moment, the LED stays lit, even when I press the switch. The dash SRS light is also lit.

I assume the LED should flash a number of times to designate a fault? Maybe the dash warning light should flash?

Any idea what the correct check prodedure is?

Thanks in advance.

 

[miro]

Seems like you should be using Pin 3 for LED DIAGNOSTIC.

 

[Hartzpartz]

I see what you mean but I think the reason you have all those pins is so each circuit can be interrogated individually? I could be wrong though!

 

[Hartzpartz]

Just looking at that wiring diagram again, I think the correct momentary switch should be "off" until pressed. The one I'm using is "off" when pressed, hence the LED is lit all the time.

 

[stats007]

d'oh.

 

[Hartzpartz]

That's better. It works now I'm using the correct switch!

With the ignition on, a quick press on the switch lights the LED. After a second or so, the LED flashes a sequence.

So all I need to know now is, what these flashes mean.

SRS circuit flashes:

3, 4, 8 and then 9.

Soft top circuit flashes:

28.

Any ideas guys??

 

[stats007]

28 I believe is no speedometer signal for the roof.

SRS:

3: Driver airbag squib
4: Front passenger airbag squib
8: Voltage supply interrupted
9: SRS warning lamp

 

[Hartzpartz]

What's a squib? Is it related to the octopus I wonder?

I was hoping the SRS fault code might point to a problem at the steering wheel contacts as the lamp comes on when the wheel is turned (when stationary).

The roof works fine but does stops halfway up. It resumes when you release and then re-press the switch! Perhaps this is normal?

On the original theme of this post, there didn't appear to be a code stored for the alarm system so I'm still non the wiser as to why that doesn't work.

 

[stats007]

It's not normal that the roof stops halfway - I believe it's related to the lack of speedometer signal.

 

[Hartzpartz]

If I drive off whilst operating the roof (at very low speeds) the warning "bong" sounds and the operation stops. I would assume from this that the control unit must be sensing a speedo signal??

 

[stats007]

That seems like a sensible assumption - however the fault code may indicate that the signal may be intermittant or invalid at a certain point.

 

[Hartzpartz]

I suppose it's a problem I can live with but has anyone heard of a cure for this problem or possible cause?

 

[NuisanceValue]

Interesting thread this

I have a '97 SL500 which in addition to the factory fitted alarm/immobiliser (with the LED's in the door handle/mirror), also has a Clifford Concept 400 alarm. Quite popular at the time apparently but many broke and screwed up the electrics and so were disabled.
This is noticeable by a red LED in the centre console and some black internal (motion?) sensors on each A pillar. I didn't try this at all until I had it checked over, but when the Clifford is armed this locks the doors etc, and gives two beeps and flashes the lights. The Mercedes fob locks the doors and I have no idea if it arms any alarm or immobiliser as there is no beeps or indicator flashes (as is described in the manual). The alarm can be set off, so is obviously armed when the Clifford is set.
The thing is, you have to lock the car with the Mercedes fob first then arm the Clifford. Other way round will set the alarm off. Similarly unlocking, Clifford first (disarmed) then unlock with remote fob. Anyone have any idea if this is correct?

I also seem to have the same airbag problem, but am going to get some independent diagnostics done, and sort it that way.

Just thought I would mention it!