Bad reading. You should get between 145 to 185 ohms at the sensor connector with the cable pulled off for a full tank.
The measurement towards the harness connector, 647 ohms is meaningless, especially if the ignition is on (it carries sense power from the cluster).
You always must make these measurements with the ignition OFF.
You may have some stray resistance on the harness to ground.
Typically you need to remove the connector at the back of the instrument cluster and make a measurement from that connector.
mrboca, thanks. Since I have cleared the code, all is good, I am not getting any messages on Instrument cluster.
I believe the way system is design is that when IC sees the low resistance in the system, it create code B112B and display on IC the message Coolant Low Level. So look like the logic in instrument cluster is that on low resistance or Mercedes call it short circuit, it will display the message Coolant Level Low.
One other observation is that when I removed the connector from washer fluid level sensor, I was getting no message. It means if there is open circuit, the instrument cluster doesn't display any messages.
Anyhow, all the connectors are connected as normal for washer fluid level sensor and coolant expansion tank level sensor. I have been driving the car and no more message.
When I get some time, I am just going to remove the instrument cluster and quickly read the resistance on IC connector IB terminals 4 and 12. This will give me full loop resistance when Coolant Expansion tank is full and windshield washer reservoir is full also. I will keep you posted.