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Discussion Starter #1
Hi Experts, My car's radiator cooling fan (suction fan) would not turn on as the car reaches beyond normal operating temp (used to be 80 degrees - now nothing even at 100+). The fan has integrated controller which is fine (at least based on what i have observed so far). This is what I did initially:

1) Tried 2 different fans, thinking the fan circuit was bad. The fan has power on red wire, ground was good and 3rd pin on the fan connector had 12v. No bad fuses.
2) When my AC used to work (now I am getting 1256 error), I used a code reader and found zero fan demand by engine demand and 20% demand by AC? Seemed like computer is detecting car being hot although temp gauge was showing 100 deg. No luck with either of the fans.
3) I then performed another test (should have done even before trying two other fans) - I disconnected PCM pin on the fan connector. The fan turned on at full speed (as expected because fan lost computer signal and protection kicked in). I confirmed and the other two fines behave the same way.
4) Next I wanted to check if Coolant Temperature Sensor was different from sensor Temperature Gauge. I disconnected the coolant sensor connect at the engine block. The temp gauge displayed zero and the fan immediately turned on at full speed (seems like computer detected open sensor and protection kicked in. This has established that there is one common temp sensor and the computer PCM driver works.

Now at this stage I am puzzled. Any ideas what I can try next (I have ordered temperature sensor for $10 - just in case).

Appreciate any clues. If things don't workout, I will create an alternate way to turn on the fan (of course it will run at full speed every time temp will reach 80 deg).

Thanks
 

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2009 E350 4M Avant Garde, My Mistress 2002 S600, Wife 2014 C300 4M Avant Garde with AMG
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NEVER, NEVER disconnect the fan plug at the radiator with the battery connected.
Been there done that and ended with a dysfunctional fan.
 

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Discussion Starter #3
Thanks. Didn't know this part. I have been careful not to disconnect when the car was on. BTW, even for testing, what i did was created a new harness which acted as an extension of the connector and gave me control over the 4th signal wire for PCM. My assessment so far is that computer is not signaling the fan to even turn on when engine is hot (the code reader specified 0 fan demand for the engine).
 

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2009 E350 4M Avant Garde, My Mistress 2002 S600, Wife 2014 C300 4M Avant Garde with AMG
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HHMMNN: The engine control unit supplies the PCM to the fan control unit.
The ECM checks itself for every engine start, so it should be ok, and should store some fault.
Using SDS????
 

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Discussion Starter #5
I used MB II iCarsoft to quickly run diagnostics. I have Xentry (using Win 7 laptop). Have some basic knowledge - used once to troubleshoot my suspension issue - without SDS, I would have been looking total wrong place).

What should I be looking at. Any particular path to the area with SDS?

Thanks
 

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Do the Fan Tests with SDS, see if you can make it run via "Actuations" at the various listed percentage speeds first, if not go for any guided testing available.
Also check that the ME2.8 is actually correctly version Coded for the Fan you have, for example "600W Temic" etc etc

HTH,
 

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Discussion Starter #7
Do the Fan Tests with SDS, see if you can make it run via "Actuations" at the various listed percentage speeds first, if not go for any guided testing available.
Also check that the ME2.8 is actually correctly version Coded for the Fan you have, for example "600W Temic" etc etc

HTH,
Thanks. I will try that. The fan installed have the same part number and power (600W). Will update my findings.
 

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Discussion Starter #8
I tried Xentry/DAS to test the fan. I was able to start the fan, increase/decrease the speed without any problems from the software. So that means:
  • ECU is to fan is fine circuit
  • Fan is good as it responds to PWM commands
  • Temperature Gauge reads fine
Any ideas, what else to look for to see why ECU is not detecting temperature above 100 degrees as hot is not kicking in?
 

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1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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NEVER, NEVER disconnect the fan plug at the radiator with the battery connected.
Been there done that and ended with a dysfunctional fan.
Being nitpicky (can you tell the confinement is getting to me yet?), you CAN disconnect a fan with battery connected. That's not a problem.

It's when you're CONNECTING the fan back on, with car on and ECU commanding 100% fan actuation? That's when you run into issues.

Same story with the fan control module.

My bet is a faulty FCM....or possible faulty AC control module somehow overriding the fan.

Try this, unplug the AC control module, then start car and let it warm up, see if fan kicks in.
 

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2003 S500
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Okay, I don't know...

Does the ECU use the same temp sensor as the instrument cluster on our cars? On most cars, they are different sensors - does anyone know that they are the same sensor on our cars?
 

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There is certainly only one ECT Sensor on the M112 / M113 Engines, I suspect the ICM get's Engine temp from ME via CAN Bus, but never looked at that ;)
 

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2009 E350 4M Avant Garde, My Mistress 2002 S600, Wife 2014 C300 4M Avant Garde with AMG
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Well, it happened when I was doing the darn oil cooler (many years ago), which required cylinder head pulls etc.
Definitely pulled the fan connector with battery on/ignition off.
Definitely connected fan with battery on/ignition off.
Would not recommend anybody to try this, as a fan is expensive on the S600.
 

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Discussion Starter #13
I will try disabling AC controller. My A/C stopped working recently so that 25% fan demand is gone. BTW, as I mentioned in the original post, it appears the coolant sensor provides input for both the Gauge and the fan because as soon as I remove the sensor wires, fan starts at full speed.
 

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Discussion Starter #14
Where is AC control module? Is it part of the console which has climate control display? Also, FCM was referred. The fan control module in my model is part of the Fan assembly. I have test 2 different fans. Both behave the same.
 

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Outstanding Contributor , SDS Guru
1998 MB E300TD, 1997 MB E36 AMG, 2001 MB E55 AMG
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Yes, it is the climate control display.
 

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Discussion Starter #16
Thanks. In the meanwhile, I got brand new coolant temperature sensor this afternoon and tried it using the near boiling water. Same results, the gauge went up to 90 degrees, No fan. Disconnected the sensor connector and it turned on.

Next I will try removing the climate control unit.
 

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I think he's fired up the parts cannon...not SDS...
 

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Discussion Starter #19
SDS gives some instructions, however, I have been using guidance provided through this group and other internet discussions.
 

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Discussion Starter #20
I performed following additional steps without any luck:

a) replaced the Climate Control unit and completely reset it.
b) verified no error codes
c) tested the fan with engine at 90 degrees. Fan did not start
d) I removed the climate control unit and restarted the car. No fan startup
e) remove the coolant sensor plug, the engine runs at full speed

Any other ideas of what might be causing ECU not to turn on the fan?
 
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