Hi Everyone,

Any help on this fault, would be gratefully received.

It's a 450 cabrio mid 2000 edition, with the old gear-stick (golf-ball) and a ZEE unit. 87kkm LHD.

Symptoms:

About a year ago, it started doing the following, while driving;

Yellow ESP light goes hard on and stays on.
Engine cuts to 1000 rpm.
Clutch disengages.
No other warning lights.
Pressing accelerator has no effect.

Pull over. Stop. Switch off engine. Restart engine and all is well.

This fault occurred randomly, with weeks or months between events. However, gradually the frequency increased until finally, one could start the car, leave it ticking over and 30 seconds later the fault occurred having not moved the car or placed it in gear.

Furthermore, with a poorly charged battery the fault occurs almost immediately, and if the revs. fall with a poor battery fitted.

My attempts at Corrective Action:

I have;

Changed the battery (new).
Checked and refitted the Earth straps in Engine bay and battery compartment.
Changed the Brake pedal switch (with new unit).
Changed the Lateral Accelerometer (with 2nd hand unit).
Checked the cables and connectors to the instrument panel.
Checked the multi-connector to the ZEE.

Diagnosis:

After much head scratching and interpretation of the circuit diagrams on a copy of WIS, I determined that there are 4 units which communicate via a CAN bus with each other;

Instrument Panel
Central Electronics Unit (ZEE)
Engine ECU (MEG)
ABS ECU (Bosch ABS controller)

Sadly, the CAN bus does not speak to the outside World. As this car was made just prior to the Jan 1st 2001 EU Directive on OBD-II it seems the sole way to communicate with it is via proprietary use of pins on the OBD connector and a Mercedes box.

So, I ordered up a STAR C3 and hard drive for a Dell D630 laptop, from our Asian friends, it has the release date 07/13.

And here are the results of the runners and riders, codes;

On the N10 (Central Electronics) = ZEE

B1000 - General internal control unit hardware fault
B1030 - Immobilizer counter overflow or CAN communication is faulty
B1016 - CAN message 'Diagnosis' from instrument cluster is missing
B1010 - Status 'Fault' of CAN controller
B1014 - No CAN message from control unit N3/10 (MEG motor electronics control unit)
B1015 - CAN message 'Kilometre reading' from instrument cluster is missing.
B1400 - Left turn signal lamp defective
B1111 - Unlocking operation failed due to short circuit

N47-7 (ABS Control Module):

C1025 - CAN bus signal No CAN message from control unit N10 (Central Electronics).
C1025 - CAN bus signal No CAN message from control unit N3/10 (MEG motor electronics control unit).
C1104 - B24/2 (Lateral acceleration sensor).

N3/10 (MEG motor electronics control unit):

39 - B24/2 (Lateral acceleration sensor)
46 - Load fault in monitoring module

The instrument cluster unit and the restraint system unit, have no faults listed.

I have not cleared/erased any codes, I am tad unimpressed that there is no time/date stamp on the stored codes !

In my initial primitive fault-finding efforts, I did disconnect the lateral acceleration sensor, so that's the stored code.

The car is always garaged and there is no obvious water ingress in any of the connectors, even the lateral acceleration sensor was pretty clean.

My best guess:

SO.... I reckon it's the N10/Central Electronics/ZEE and precisely the CAN bus Controller chipset therein.

BUT..... why does it work at all ?

I am an electronics engineer by training, and in my world when a chip fails, it fails, so I find it odd that a CAN bus controller can fail after a period of time, yet work after a reset.

I am about to extract the ZEE PCB module and carefully open it up to check the electrolytic capacitor on the board, which I am guessing is across the 12v rail or internal voltage regulator.

If I have to replace the ZEE unit, the STAR software (XENTRY-DAS) is saying "Special function 'Immobilizer' must be performed after exchanging control unit N10 (Central Electronics)"

I have a nasty feeling that this 'special function' will require a "TAN Code" pin-code and therein lies another issue.

Also, I am concerned that the alarm-immobiliser key-fobs will need to be 'teached-in' if the ZEE is changed.

Has anyone had direct experience of changing a ZEE and if one can obtain a 'clean' or re-manufactured ZEE which can assume the identity of the failed unit ?

You will notice I have studiously avoided involving a Mercedes Stealer, thus far.

Cheers, and thanks for your input.

Arkon.