Avoid costly ECU replacements by first attempting a repair of the malfunctioning ECU. Not all ECUs can be repaired depending on the severity of the malfunction, but diagnosis is free, and no charge is levied for fault diagnosis.
If the ECU cannot be repaired, or another used ECU needs to used to replace the original, we can copy the version coding from old to new. If the EEPROM has become corrupt, as they are known to do, a fresh coding can be written using the Mercedes SDS tool.
Central to the climate control system in your vehicle is the N22 or Climate Control Module.
Faults with this system typically present themselves as being faulty inputs, however depending on the severity of the system failure, the N22 may have been damaged as well.
Catastrophic failure of the blower or regulator can damage the N22, as can failure of servo pumps or other external switched devices.
Debugging the system :
Ensuring the blower and regulator are inspected and repaired, or replaced with the correct replacement parts.
Many different spec blower regulators have been used over the years, so the correct replacement is vital to correct operation.
Starting in the eighties with electronically regulated blowers, the N22 generates a signal to the blower regulator.
This signal is generally in the 1V to 6V range, and can be probed at the regulator harness when working correctly.
Power and ground can be checked at the same time to ensure they are getting through.
N22 modules typically have diagnostic modes which give you error messages and sensor input data.
Determine the correct button input sequence to activate your diagnostics mode.
It varies from model to model, so check with your dealer, or check online.
The N22 module contains several output solid-state relays.
You can't hear them click, but they control many output devices which active switches, external solenoids, devices signals.
When these are not working, the N22 must be repaired!
When sending in your N22, include the blower regulator as well. We'll test both parts to ensure the whole system will work correctly when you plug it back in.
Removable Softtop Module (RST)
Opening and closing problems associated with the convertible roof can mostly be traced to mechanical malfunctions such as faulty micro switches, hydraulic pumps, and electric motors.
For example, if your early SL has an instrument cluster failure, the RST will not operate, as the VSS signal comes from the instruments.
However, the ECU can also succumb to electrical malfunctions, and then must be replaced or repaired.
Our test bench equipment can quickly diagnose ECU problems and help trace your main source of problems.
Multiples versions of the RST module exist for the R129 :
A129 820 00 97 : MY 1990 - 12/93, three electrical connectors
A129 820 24 26 : MY 1993 - 1994, three electrical connectors
A129 820 31 26, A129 820 39 26 : As of 09/95, two electrical connectors
When diagnosing a convertible top issue, a schematic of the opening and closing sequence is helpful. The micro switches involved in the process are critical to correct operation. The following diagrams show switch timing, and DTC errors.
A video showing the operation of the RST module, using correct timing of micro switches can be seen below.
Diagnosing a faulty micro-switch using the built-in diagnostics can be seen below.
Module Cloning and Version Coding
Starting in the mid 90s, Mercedes slowly started introducing version coding to its ECUs, which customized the vehicles options to the ECU. The correct coding was critical towards the operation of the ECU, because it would rely on other systems and components to transfer data for proper operation. Thus parts became tailored for the vehicle they were intended for.
Swapping out another ECU, in the event of failure, now requires the Mercedes SDS tool to version code the new part. Alternatively, aftermarket microchip readers were developed which didn't require any diagnostic equipment, and were able to read and write data from specialty automotive EEPROMS and MCUs. These tools are a more low-level approach to coding chips, and require PCB and soldering experience, which is not recommended for the novice DIYer.
MBCluster has both the Mercedes SDS tool, and aftermarket chip readers and can implement either tool depending on the situation. The chip readers we use are latest versions of the XPROG, CARPROG, and UPA readers. We can clone the data from one ECU to another, using chip readers, and program clean version codes to the ECU aswell.
Copying the version coding and DAS2 information from a 1996 W210 can be seen below. If the chip cannot be talked to directly from the PCB in situ, then it needs to be removed, which was the case here.
Sending In Your Unit
Fill out the online Repair Form, and include it with your unit :
International customers, ex. United states, Europe, must fill out the customs documented, and follow the shipping instructions available here.
Bundle the unit up in ample padding and place it in a sturdy box. Address is located at the bottom of the Repair Form. Please note : Only USPS may be used for American shipping! Canadian shipments may use private couriers such as UPS, FedEx, etc., all other countries must use their federal postal services.
Once we have received the unit and diagnosed the fault, we will e-mail an update. If you are satisfied with the diagnosis, we will begin repair accordingly. Final payment is done using the easy PayPal system, with Invoice sent in the email exchange. If for whatever reason, you have decided to decline service, or service is not possible for your unit, a shipping charge is required to send it back.
ECU/ECM Repair, Module Cloning and Version Coding
Pricing is in Canadian Dollars (CAD).
Note: All Canadian residents must add their province's applicable taxes (HST or GST).
United States and other foreign countries do not add taxes.