[ClassicRed]

Is the immobiliser (DAS) the culprit?
Probably not, because:

Your electronic ignition switch (EIS) is already accepting the key – it released the steering lock and powered the cluster.

With a DAS block you usually see “START ERROR” in the LCD (or a fast-blinking red LED on very early clusters) and the starter relay is never energised. You have no dash at all until you jumper the B+ lead, which points to a power-distribution fault, not authorisation.

When the alarm battery is flat or the PSE module loses power, the siren will trigger the instant you try to crank – exactly what you experienced. A failed PSE is common and unrelated to the immobiliser.

 

[ClassicRed]

Now, I have this follow-up question: You mentioned "PSE module" and a failed "PSE". are you referring to one and tha same component, tha pump, or a module to tha pump???

In Mercedes-speak “PSE” (Pneumatic System Equipment) is a single, self-contained unit that lives in the boot (trunk) of your SLK (R170). People call it lots of things—PSE pump, PSE module, central-locking pump—but they’re all talking about one piece of hardware

What’s inside the black foam-wrapped box (part N69/1)

Electric vacuum / pressure pump Multi-port air manifold with several solenoid valves	Makes pressure/vacuum for door, boot-lid and fuel-flap locking; supplies lumbar bladders on some models
Electronics board (power driver + CAN/LIN logic)	Talks to the body network, measures pressure, times how long the pump runs, and tells the ATA alarm if a door fails to lock / unlock

Because the motor, valves and control electronics share the same housing, the workshop literature sometimes calls it a pump (mechanical bit) and sometimes a module (electronic bit). In practice you replace or repair the whole assembly as one part.

but it is very rare or even impossible to repair, he prefers the ease of replacing it, and the maximum invoice

A couple of practical notes for fault-finding:

Power & fuse: The PSE has its own 30 A fuse in the right-hand fuse box; if that feed is missing the car may lock you out and the alarm siren will shriek the moment you disturb a door handle.

Common failures: water ingress (boot seal), overheated control-board resistor, or a broken pneumatic nipple. Any of those will disable central locking and confuse the alarm, exactly the symptoms you described.

Alarm siren ≠ PSE: The screaming piezo siren is a separate unit (under the wiper tray on an SLK). It just takes a “panic” line from the PSE/ATA to decide when to sound. A dead PSE often leaves that line in a permanent “alarm” state.

I had alarm problems in the past, and it came from the battery inside which was HS, I replaced this one with a second-hand one a couple of months ago and for the moment I no longer have any problems 🤞🤞

So when I wrote “PSE module” or “failed PSE” earlier I meant the same central-locking vacuum pump assembly—not two different components. If your pump housing, its plug pins, or the little PCB inside are corroded or cracked, replacing or rebuilding that one box will cure both the locking fault and the false-alarm behaviour.

then I wonder if the N10/3 module would not have its say


But some members of the forum are much more competent than me, and who I hope will come to help as much as possible, as they did for my starting problem. 👍

* Download the pdf, you will see why I am also going for N10/3, but be careful, my model is from 2002, yours is older, so there are differences.

 

[ClassicRed]

When you only turn on the ignition, have you checked that your ECU/computer is properly supplied with 12 volts?

 

[ClassicRed]

help? SLK 230 battery cut-off relay problem

Any help with the known K56 battery cut-off relay problem on 98 SLk230 ?? I replaced the batt and alt before realizing they weren't the problem so both test good. After I replaced the battery cut-off relay, nothing changed. The "G" post on the relay has 19+V and the "battery" post has 12.2V...

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