Nikola T.

Rear window electric defroster on W211 E220 CDI Avantgarde Station Wagon (kombi) failed without special reason at 350.000 km (217.000mi). SAM controlling rear wind defroster-heater is located left of trunk. Open left cover with emergency triangle label and remove sound dampening material to uncover the rear electronic modules holder.

Check relay (E) operation by listening the click sound on rear SAM, following the »defrost« button operation on air condition panel.



Check on rear SAM the nr.10 fuse 40A. If voltage is present only on one side (closer to relay) replace the fuse.

Check if voltage come to rear window. Open covers around window and measure voltage on red/yellow wire on filter located near defrost traces on right side of window. If voltage is very low. Less than 1-2V disconnect BLACK faston with red/yellow wire from filter and measure voltage again. If voltage is then 12V or same as on 40A fuse (nr.10) the problem is in connector nr.20 located behind of rear SAM.



Over heated faston, connector and wire

connector melted


clean pin 5 within connector nr.20 with sand paper


While defroster properly working the current is in region of 15A. Contact from rear SAM via connector nr.20 is not properly designed for such a current!!.
Operation of rear defroster is limited by SAM to 20min operation, depending on outside temperature.

There are two ways to fix the problem.

If plastic around the last male pin in connector nr.20 is not totally burned you can clean the contact and replace connector and overheated wire. Prepare new wire 10cm long 1,5mm2 (4˝, AWG 15) and crimp new contact. Old wire will be too short for repair because copper became brittle if over heated. Connect new wire with red/yellow wire.



Connect new wire first and then connector. I made a mistake when making bigger hole in connector. You should just clean connector plastic and make hole just big enough for new faston.
Insert faston directly on pin 5 without connector first.
Of course you can replace connector with new one, but you saw the result with original.



For second solution follow next picture.


I inspected SAM internaly, but for this fix it is not necessary.
I have Xentry, but this was very simple repair and you don't need it.



Excessive heat melted plastic distance holder.


Hope to help you to repair your rear window defroster.

IMPORTANT !!!
After rear defroster repair now also BOOSTER HEATER (also called AUXILARY HEATER) STARTED TO WORK AGAIN !!
Most probably they are somehow functionally related.

Nikola T.

Nikola T.

FUSES and RELAYS in REAR SAM N10/2 (located on left side in trunk)

F001 30 A Driver Seat Power
F002 30A Passenger Seat Power
F003 7.5A Navigation
F003 7.5a Parktronic
F003 7.5A Tire Pressure Control
F003 7.5A TV
F004 20A Fuel Pump
F005 20A –
F006 40a Audio GateWay
F007 15A Emergency Light T model
F008 7.5 Antenna Module
F009 25A Roof Unit
F010 40A Window Defroster Rear
F011 20A Tailgate Control Unit
F012 15A Plug Socket Trunk
F013 15A Plug socket Rear
F013 15a Pneumatic Adjustable seat
F014 5a –
F015 10A Fuel Tank Locking
F016 20A Heated Seats Rear
F017 20A Trailer Power Supply
F018 20a Trailer Control Unit
F019 20a Electronic control unit for additional rear light
F019 20A Pneumatic Adjustable Seat
F020 7.5A Window Shade Rear
F020 30A 3rd Stop Light
RELAY:
Relay kA Fuel Pmp
Relay kB Relay 2 Circuit 15R
Relay kC Reserve 2
Relay kD Rear Wiper
Relay kE Rear Window Defroster
Relay kF Relay Ciruit 15R
Relay kG Fuel Filler Cap Polarity Change 1
Relay Relay kH Fuel Filler Cap Polarity Change 2 Relay

FUSES ON DRIVERS SIDE OF DASH
F021 30A Door Control Unit Rear Right
F022 30A Door Control Unit Passenger
F023 30A Passenger Set Adjustable Memory
F024 25A Keyless Go
F025 20A Additional Heating with/without remote start
F026 7.5A CD Changer
F027 Reserve –
F028 5/15A Radio
F029 7.5A Steering Column Module
F029 7.5A Steering Column Module
F030 7.5A Diagnostic Socket
F031 5A Switch Off Relay
F031 5A Top switch panel
F032 30A Door control unit rear left
F033 30A Door control unit driver
F034 30A Driver seat adjustable/memory
F035 5A Weight sensoring system
F036 25A Heated seats front
F037 5/15A Conrol unit Height Adjustment
F037 5/15A Airmatic F038 – Reserve
F039 5A Bottom Switch Panel
F040 10A Steering wheel heating
F041 5A Central Gateway
F042 7.5A Engine Control Module
F042 7.5A Fuse and Relay Box Driver

FUSES and RELAYS - FRONT (in engine area on left side)
F43 15A –
F44 15A –
F45 7.5A –
F46 7.5A –
F47 5A ESP,SPS,PML &BAS control unit N47-5
F48 7.5A Restraint Systems Control Unit N2/7
F49 7.5A –
F50 5A –
F51 5A –
F52 7.5/10A Rotary light swich S1, Cluster, Glove Compartment
F53a 15A Fanfare horn relay N10/1kO
F53b 15A a side always powered b side no power with ignition off
F54a 15A Cigarete Lighter
F54b 15A a side no power with ign. Off b side always powered.
F55 7.5A – F56 40A Wiper Motor
F57 25A –
F58 15A Ignition Coils
F59 15A /20A Starter Relay
F60 10A Oil cooler fan
F61 40A Electric air pump
F62 30A/20A SEQ Pump Control relay N10/1kM
F63 15A Circuit 87 relay, engine N10/1kl
F64 7.5A Rotary light switch, more
F65 20A EIS EZA Unit N73 Steering lock unit N26/5
F66 7.5A Right/left front lamp unit E2, E1
RELAYS:
Relay kI Circuit 87 relays, engine
Relay kJ –
Relay kK Circuit 87 relays chasis.
Relay kL Starter Relay
Relay kM SEQ ASG Pump Control Relay
Relay kN Circuit 15 relay
Relay kO FAN Relay Module
Relay kP Cirucit 15R relay
Relay kQ –
Relay kR Air pump or oil cooler fan relay
Relay kS AirMatic Relay K67
Relay kT Cutoff relay to interruptible loads K75

FRONT PRE-FUSE BOX F32 (under front passengers footwell - right)
F70 150A –
F71 150A M4/7 Electric suction fan with integrated control
F72 50A A7/3 Traction system hydraulic unit
F73 40A A7/3 Traction system hydraulic unit
F74 40A K67 Airmatic Relay
F75 40A N10/11 Passenger SAM P
F76 40A N22 Air Conditioning Control Module
F77 – Reserved

REAR PRE-FUSE BOX F33 (in trunk in front of battery)
F78 200A N10/1 Driver SAM D
F79 200A N10/2 Rear SAM-R
F80 150A N10/1 Driver SAM D
F82 150A N3/10 Control Module
F83 10A Reserved
F84 5A N82 Battery Control Modle
F85 5A N112 Communcation Platform and A35/11 VCS
F86 5A x58/1 Interior Socket
F87 40A M40/1 Fneumatic Pump of Dynamic Seat Control
F88 30A N121 Trunk Closer Module

hex87

Your guide saved me a lot of time on figuring out whats wrong by myself. I was able to locate the issue very easily and for me the heat damaged the SAM so I bought a 2nd hand one with same part code. Now before installing it Im thinking... dont you think it would be beneficial to add an additional fuse like 20A maybe in the area where I connect the old wire with the additional 10cm extension? The fuse that is placed on the front of SAM is 40A which seems... quite a lot considering it normally operates around 15A. Im just thinking how to prevent same thing from happening again.

Nikola T.

HEX87, glad to help.
40A fuse for rear defrost seems a lot, especially because normal consumption is cca 15A, but you have to take into account that for a split of second when you switch ON heater element, resistance is very low and in that first moment high current peak occur. Therefore higher value fuse is necessary to cope with that.
If connection within SAM unit from + via relay "E" to 40A fuse is damaged and can't cope with that current this signal can be used to energize auxiliary relay. Do not forget to use auxiliary fuse of 40A in series with relay contacts too!

hex87

Thanks a lot for your replay! It came in exactly when I was working on the rear SAM That makes a lot of sense what you said, now I understand why it's 40A. I ended up having 3 rear SAM units trying to fix my rear lights issue and Im pretty sure the one I installed now is fine (I did the measurements like you suggested) so I used your method 1: removed the damaged wire part, done an extension + new connector and plugged back into pin 5. So far so good (in terms of the defroster, not lights ), it switches on and heats the window. I'll test it in action soon when colder days come ❄☃

Thanks a lot