MB Medic Mercedes-Benz Repair Guides, Service, How To DIY
How to troubleshoot the Mercedes-Benz air conditioning system, read sensor data, and reset the control unit.
Troubleshooting Instructions
Entering Diagnostic Trouble Code (DTC) Display Mode
1) Turn the ignition on. Press the down arrow push button until “LO” is shown in the A/C-heater control panel temperature display window.
2) Within 20 seconds, simultaneously press the REST and defrost push buttons for over 2 seconds. The Light Emitting Diode (LED) in the recirculated air push button will blink, and the display window will show “di R”.
3) Press the AUTO push button repeatedly, recording each DTC, until all DTCs are displayed. Permanent malfunctions are displayed first. See DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION tables.
4) If no permanent malfunctions are stored, the display window shows “End.” Press the AUTO push button again. Intermittent DTCs will be displayed. Intermittent malfunctions are recognizable by the degree (°) symbol displayed along with the DTC (example: “04 °”).
5) If no intermittent malfunctions are stored, the display window shows “En° d.” Proceed to erase DIAGNOSTIC TROUBLE CODES.
Erasing Diagnostic Trouble Codes
1) After the display window shows “En° d,” press the AUTO push button again. The display window should show “dE L” (delete).
2) To erase DTCs, simultaneously press the down and up arrow push buttons for over 5 seconds. The display window should show “- –.” If not erasing DTCs, press the AUTO push button. The permanent DTCs will again be displayed. Proceed to exit DTC DISPLAY MODE.
Exiting DTC Display Mode
Simultaneously press the down and up arrow push buttons until the pre-selected “72 °F” temperature setting is displayed. Turn the ignition off.
DCT error codes list:
B1226 – In-car temperature sensor (B10/4)
B1227 – Outside temperature indicator temperature sensor (B14)
B1228 – Heater core temperature (B10/1)
B1229 – Heater core temperature (B10/1)
B1230 – Evaporator temperature sensor (B10/6)
B1231 – ECT sensor (B11/4)
B1232 – Refrigerant pressure sensor (B12)
B1233 – Refrigerant temperature sensor (B12/1)
B1234 – Sun sensor (B32)
B1235 – Emissions sensor (B31)
B1241 – Refrigerant fill
B1416 – Coolant circulation pump (M13)
B1417 – Duovalve (Y21y1), left
B1418 – Duovalve (Y21y2), right
B1419 – Electromagnetic clutch (A9k1)
B1420 – Idle speed increase
B1421 – Pulse module (N65)
B1422 – Series interface (K1) connection to instrument cluster (A1)
B1423 – Switchover valve block (Y11)
B1424 – Activated charcoal filter actuator (A32m2) open
B1425 – Activated charcoal filter actuator (A32m2) closed
B1432 – Non-USA DTC
B1459 – Series interface (K2) connection to instrument cluster (A1)
B1462 – Wide open throttle (WOT) position signal: diesel engines
Climate control as a diagnostic tool
READING SENSOR VALUES
1) Turn the ignition on. Simultaneously press the down and up arrow push buttons until the pre-selected “72 °F” temperature setting is displayed. Press the AUTO push button.
2) Press the REST push button for more than 6 seconds. The display window will alternately show “01” and an in-car temperature of “72 °F”, or “LO” if there is an open circuit or “HI” if there is a short circuit.
3) The next ascending test step is displayed by pressing the windshield air distribution push button. The next descending test step is displayed by pressing the footwell air distribution push button. See the SENSOR VALUE DIAGNOSTIC TROUBLE CODE (DTC) IDENTIFICATION table. Press the REST push button to exit reading sensor values mode.
01 = In-car temperature sensor
02 = Outside temperature sensor
03 = Left heat exchanger (heater core) temperature sensor
04 = Right heat exchanger sensor
05 = Evaporator sensor
06 = Coolant temperature
07 = Refrigerant pressure in bar
Refrigerant pressure changes with ambient temperature, engine speed, airflow, and compressor operation. One pressure value does not confirm the correct refrigerant charge. Do not add refrigerant without checking for leaks and measuring the charge with approved A/C service equipment.
08 = Refrigerant temperature sensor (23*9 = 23.9deg C)
09 = Nothing
10 = Blower control voltage (great for evaluating blower controller problems)
11 = Emissions sensor (B31) e.g. 3.1 = 31.v
12 = Sun sensor 4.2 = 4.2v
20 = Auxiliary fan control 6.1 = 6.1ma (max 10ma)
21 = Engine speed
22 = Vehicle speed
23 = Circuit 58d e.g. 99 = 99% of battery voltage
24 = BATTERY VOLTAGE e.g. 12.5 = 12.5v
30 = Left rear air conditioning heat exchanger temperature sensor (not all vehicles; obviously)
31 = Right side
32 = Rear evaporator temperature sensor
33 = Blower control voltage rear 0.8(MIN) – 6.0(MAX)
34 = Left rear temperature selector
35 = Right side
38 = Software status e.g. 37 rear air conditioning
38 = Hardware status e.g. 37 , rear air conditioning
40 = Control module version software status (?)
41 = Control module version menu hardware status
42 = Control module variant code 1st number
43 = Variant code second number.
Record all fault codes and sensor readings before clearing the climate control memory. Clear the codes only after completing the repair, then operate the system and scan it again.
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Just got price for ac condenser $3200 for a 2003 SL500 (42,000mi) Mercedes 42,000 mi
need earlier version 2002 without digital readout
Having 3 different MB models – all of them start displaying sensors after pressing REST, but here is where the different scrolling applies. (when you have climatronic with no REST button, you need to use advanced scanner, or replace climatronic with one having REST)
-on single zone R129 you scroll by pressing fan buttons
-on dual W210 you scroll by pressing left and right Auto
-on 4-zone W211 you scroll by pressing left temp adjustment.
4 zone displays more sensors
00 has to be inside cabin per my observation, so my guess 00 and 01 are front and rear of the cabin, but could never find official data.
Good info, but does not explain how to use the data.
Per my experience you need to read the sensors at least twice in different conditions.
1 on cold car before engine start and before sun can warm the cabin. All the temperature sensors should show the same, usually with +- 3F differences. Very common evaporator sensor failure will show temperature very high
2 a minute after restarting car that was sitting on hot parking lot. This will allow to see if compressor is building the pressure and how the cores work.