Here’s a DIY to ‘fix’ this issue. Please note that this ‘fix’ is only for areas where Adblue will never freeze at -11 degrees. Here in Sydney, Australia, this car will never experience those temperatures.

Symptoms:
- 2013 W166 ML250 Orange Check Engine Light comes up.
- Blows a lot of whit exhaust smelling like ammonia
- Adblue consumption high. Uses remaining tank within 3 days of light appearing.

Diagnosis:
- Error Code 205B98 Adblue Tank Temperature : Excess Temperature
- Error Code 205C16 Adblue Tank Temperature : Short circuit to earth

The proper fix:

• Replace Adblue Preheater assembly Part No. A1664710775
• This includes the heating element, level sensor and temperature sensor.
• Aftermarket Part costs AUD$1700
• Wreckers selling used ones for AUD$1000
• Did not enquiry with Dealer

Background information:
From research this issue is common in these Bosch units. There are detailed DIYs for VW Golf TDIs and BMW X5s, but not Mercedes ML250 which has slightly different wiring.

The temperature sensor (and level sensor) use resistance to feed information to the control module. This DIY can be applied to the Adblue level sensor issue which also seems to be quite common.
It seems that a 10K resistance is the normal temperature level. From my research, I was able to find this info.

• Resistance value at a temperature of -10°C: 55 k
• Resistance value at a temperature of 0°C: 32 k
• Resistance value at a temperature of 10°C: 20 k
• Resistance value at a temperature of 20°C: 12.5 k
• Resistance value at a temperature of 25°C: 10 k
• Resistance value at a temperature of 30°C: 8 k
• Resistance value at a temperature of 40°C: 5 k

As I live in Australia where the temperature never will never freeze Adblue (-11 degrees), I figured that feeding a 10K resistance will solve the issue.

This site provided a wealth of information, for the BMW X5. https://www.bimmerfest.com/forums/sh...667126?page=24

DIY - Sorry for the lack of photos, didn’t think about writing this up at the time. But was frustrated with the quoted cost of repair and thought the community could benefit from this.

Step 1
Remove the rear right side (driver side in Australia) wheel.

Step 2
Remove the wheel arch cover

Step 3
Remove the plastic cover under the Adblue tank

Step 4
Remove the two right side bolts holding the Adblue tank. This will allow the tank to drop a few centimeters to allow access to the harness. I didn’t remove the tank as I’d just filled it with 28 liters of Adblue.

Step 5
You can now see the Adblue tank harnesses. The two you need sit next to each other at the rear of the tank. One has 4 wires, the other has 3 wires. It is a little tight, but I managed to unclip the connectors from the tank. One clips by pulling to the right direction of the car, the bigger one unclips by pushing to the left direction. Disconnect the connectors.. you need the connections that connect directly to the heating element in the Adblue tank, not the connection that runs to the car.



** This image is of a BMW X5 harness. Note that on the W166, the black thin wire is missing, so the white thin wire needs to be connected to a resistor and jumpered onto the grey base wire. **

The temperature sensor wire is the white third thin wire on the three wire connector. (The other wires are thick). I measured 0 ohm resistance between this wire and the grey wire base on the other connector. This was the cause of the “short to ground” error.
Cut this white wire and connect a 10K resistor to the short wire from the connector. The other side of the resistor needs to be connected to the grey base wire on the other connector.
I tried soldering, but couldn’t maintain the connection after bending the wires, so I ended up using a screw terminal to connect the resistor to the wires, and heat shrinking, then some silicon to seal it against the elements.
After retesting the resistance and confirming that there was now 10K Ohms between the white temperature sensor wire and grey base wire, I reassembled everything.

The Check Engine Light went away after two restarts of the car.

If you’re getting the Level Sensor Error, you can use this method to connect 10K resistors to the shorted connections, but need to be sure to top up Adblue as you will lose the ability to monitor Adblue Levels.

If you live in a climate where it reaches -11 degrees, XModex say they are working on the kit for the W166.

Hope this helps people stuck with this issue, and don’t want to fork out $1.5k+ for the fix.

Total cost for this fix was under $10, and 45 minutes of labour.

 

 

Similarly, the other W212 E350 BlueTEC?
A2124710575
https://mbworld.org/forums/m-class-w...r-failure.html

Temperature Sensor and Level Sensor both in disable
Connection method please me

 

May I know which wire suppose to connect with 10k ohm resistance for level sensor?

 

Hi GL350,
Just a confirmation please For ML250 W166 with only temp sensor short circuit. Cut both thin white and base grey and jumper with 10k resistor OR should i keep base grey and just have thin white jumperd on it (T JOINT)??????

Thanks

 

Or you can just buy the parts to fix the problem.. if you don't like spending money on cars then go buy a Camry

 

What wattage resistor did you use please?

 

hi, Did you get the answer. Wanna know too

 

hi. did you get the right wire for level sensor
?

 

did you figure out the answer
I done the temperature sensor and also have the level sensor as error