Help for Coolant Level Warning
12-03-2021, 01:14 AM
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Help for Coolant Level Warning
Hi all,
I'm new here, so take it easy please. I recently purchased a CLK55 from 2004. When I received the car, it was showing the low coolant warning on the dash and as many other owners have found the coolant level is fine. So far my searching has not definitively pointed to a solution, so let me explain my findings and then maybe someone can add more.
On finding the warning and the coolant level was fine, I decided to investigate further. Initially I hooked up my copy of Star to see if there was an error, as usual the first pass revealed 10,000 errors (or so it seemed). After a quick review of the errors, I cleared them and on restarting the car, the low coolant waring immediately returned and now the error 2073-004 - Suction Fan Error (open circuit) was the only engine, A/C and instrumentation error - I thought great a way forward. Star then provided a test to operate the fan which passed, the fan can be controlled and works effectively at all speeds, but still I had the error.
Going back to basics, next I checked the resistances across coolant and washer sensors (they both passed), further unplugging the coolant level a sensor threw-up the sensor error which cleared when I replugged in the sensor - no issues here.
Continuing in the same approach, since the fan error is for an "open circuit", I tested the wires from the Front SAM and the engine ECU to the fan, coolant level and the washer sensors (as appropriate) - all passed, no line breaks were found. Now I'm getting frustrated.
With the hand held temperature probe I decided to run the car engine and see what was happening. With Star listing the fan requirements requested by the engine and the A/C I watched the fan operate exactly as requested and the temperature readings on Star and the instrument panel correlated with my temperature probe. Again the only error on the A/C, engine and instruments is 2073-004. That said during an earlier engine run, I did once experience the fan accelerate to full speed (default error operation) when the coolant reached around 100 degC and then quickly drop to 80 degC without the fan stopping, at this point I had opened the Star page for fan demand and noted both the A/C and the engine were posting zero fan demand. My guess is the fan has a built in temperature sensor and will default to high speed if a trigger point is reached.
I then decided to pull the fan to check it out and noticed it was new (replaced recently by the previous owner). Unfortunately as this was an auction purchase, I have no ability to contact or communicate with the previous owner.
More research has revealed several options:
- Back in 2004 MB released service bulletin P-B-20.40/26a which exactly describe my symptoms and requested the installation of a wiring adaptor between the fan an ECU (A209 540 56 35) to resolve the issue. My car doesn't exactly fit the chassis numbers but it may be a fix.
- For the 203 C class, I saw a post where it was being stated that a replacement fan may need to be coded to the car (instrument panel - from memory) - I can't see any options to adapt the fan to the car in Star (but I'm probably looking in the wrong place)
- The Engine ECU needs to be replaced - not sure why when everything works fine
- The fan needs replacing again - not sure why when Star states the fan is OK
To me there appears to be a communication issue between the fan and ECU. I haven't yet considered applying an oscilloscope to the fan controller line (as I have no idea what I'll be looking for). Has anybody able to comment on the solutions or should I be looking elsewhere.
Thanks,
Andrew...
I'm new here, so take it easy please. I recently purchased a CLK55 from 2004. When I received the car, it was showing the low coolant warning on the dash and as many other owners have found the coolant level is fine. So far my searching has not definitively pointed to a solution, so let me explain my findings and then maybe someone can add more.
On finding the warning and the coolant level was fine, I decided to investigate further. Initially I hooked up my copy of Star to see if there was an error, as usual the first pass revealed 10,000 errors (or so it seemed). After a quick review of the errors, I cleared them and on restarting the car, the low coolant waring immediately returned and now the error 2073-004 - Suction Fan Error (open circuit) was the only engine, A/C and instrumentation error - I thought great a way forward. Star then provided a test to operate the fan which passed, the fan can be controlled and works effectively at all speeds, but still I had the error.
Going back to basics, next I checked the resistances across coolant and washer sensors (they both passed), further unplugging the coolant level a sensor threw-up the sensor error which cleared when I replugged in the sensor - no issues here.
Continuing in the same approach, since the fan error is for an "open circuit", I tested the wires from the Front SAM and the engine ECU to the fan, coolant level and the washer sensors (as appropriate) - all passed, no line breaks were found. Now I'm getting frustrated.
With the hand held temperature probe I decided to run the car engine and see what was happening. With Star listing the fan requirements requested by the engine and the A/C I watched the fan operate exactly as requested and the temperature readings on Star and the instrument panel correlated with my temperature probe. Again the only error on the A/C, engine and instruments is 2073-004. That said during an earlier engine run, I did once experience the fan accelerate to full speed (default error operation) when the coolant reached around 100 degC and then quickly drop to 80 degC without the fan stopping, at this point I had opened the Star page for fan demand and noted both the A/C and the engine were posting zero fan demand. My guess is the fan has a built in temperature sensor and will default to high speed if a trigger point is reached.
I then decided to pull the fan to check it out and noticed it was new (replaced recently by the previous owner). Unfortunately as this was an auction purchase, I have no ability to contact or communicate with the previous owner.
More research has revealed several options:
- Back in 2004 MB released service bulletin P-B-20.40/26a which exactly describe my symptoms and requested the installation of a wiring adaptor between the fan an ECU (A209 540 56 35) to resolve the issue. My car doesn't exactly fit the chassis numbers but it may be a fix.
- For the 203 C class, I saw a post where it was being stated that a replacement fan may need to be coded to the car (instrument panel - from memory) - I can't see any options to adapt the fan to the car in Star (but I'm probably looking in the wrong place)
- The Engine ECU needs to be replaced - not sure why when everything works fine
- The fan needs replacing again - not sure why when Star states the fan is OK
To me there appears to be a communication issue between the fan and ECU. I haven't yet considered applying an oscilloscope to the fan controller line (as I have no idea what I'll be looking for). Has anybody able to comment on the solutions or should I be looking elsewhere.
Thanks,
Andrew...
