Question about Mercedes-Benz C200

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Fault finding hi, this seems to be a comman fault on c200 merc, the cooling fan system, the fan is in perfect working order so there is nothing wrong with fan itself. the electronic relay pack that fits under the wheel arch as been replaced and so as the engine sensor, if you disconnect the sensor the fan will run, if you turn on ac the fan will not run,when the engine is at high temp it does not work,i do believe that the temp sensor works on resistance and not voltage sending a signal to the electronic unit which i assume is behind the dash board if there are any other main electric mechanical type relays that bring in the fan i don't know where it is located.i also realize that the fan runs at different speeds depending temp and ac basically what brings the fan in?

Posted by Anonymous on

4 Suggested Answers

6ya6ya
  • 2 Answers

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Posted on Jan 02, 2017

Tech Jenkins
  • 359 Answers

SOURCE: Radiator fan problem

Call up the dealer and ask what commands the fans to come on once the car reaches operating temp, on alot of imports, there is a fan control box of some sort that actually sends the sig to the fans to come on.

If it's the temp sensor and the computer tells the fans to come on you could be looking at a faulty computer.

This would deffinetly be worth taking to the dealer to diagnose so that you don't keep wasting your time and money chasing a ghost.

Posted on Sep 02, 2008

drsinister69
  • 2317 Answers

SOURCE: Electric Radiator Fan Does Not Come On

DTC P0480 - COOLING FAN CIRCUIT

Circuit Description

The cooling fan is controlled by PCM through the fan relay based on inputs from ECT sensor, IAT sensor, A/C selector switch, A/C refrigerant pressure switch and vehicle speed sensor. PCM controls cooling fan by grounding cooling fan control circuit which turns on cooling fan relay.

The fan relay will be commanded on when ECT reaches 223°F (106°C) or greater, A/C is requested or vehicle speed is less than 38 MPH. Cooling fan relay will also be commanded on regardless of vehicle speed when a DTC is set requesting cooling fan to be on, ECT is 304°F (151°C) or greater, or A/C refrigerant pressure is high. Cooling fan may also be commanded on when engine is not running, on certain conditions.

Conditions for setting DTC:

Battery voltage greater than 9.5 volts.

Cooling fan fault line detects a malfunction for 6 seconds.

1. Check the cooling system. Ensure coolant level and belt tension are correct. Adjust/repair as necessary. After repairs, go to step 23). If no adjustment or repairs were required, go to next step.

2. Turn ignition on, with engine off. Using scan tool, check if cooling fan is operating with ECT at less than 209°F (98°C). If cooling fan is off, go to next step. If cooling fan is on, go to step 4).

3. Command cooling fan relay on. If cooling fan operates, go to step 23). If cooling fan does not operate, go to step 5).

4. Turn ignition off. Disconnect PCM harness connector. If cooling fan turns off, go to step 23). If cooling fan does not turn off, go to step 6).

5. Disconnect cooling fan relay harness connector. Using a test light connected to ground, probe battery feed circuits in relay harness connector. If test light illuminates on both terminals, go to step 7). If test light does not illuminate on both terminals, go to step .

6. Disconnect cooling fan relay harness connector. With test light connected to ground, probe battery feed circuit in relay harness connector. If test light illuminates, go to step 9). If test light does not illuminate, go to step 10).

7. Connect a jumper wire between cooling fan relay battery feed and cooling fan battery feed circuit. If cooling fan operates, go to step 11). If cooling fan does not operate, go to step 12).

8. Repair open in battery feed circuit. After repairs, go to step 23).

9. Repair short to voltage in cooling fan battery feed circuit. After repairs, go to step 23).

10. Connect test light battery voltage and probe cooling fan control circuit. If test light illuminates, go to step 13). If test light does not illuminate, go to step 21).

11. Connect test light to battery voltage and probe cooling fan control circuit. Using scan tool, command cooling fan on. If test light illuminates, go to step 14). If test light does not illuminate, go to step 15).

12. With jumper wire still connected, disconnect cooling fan harness connector. Using test light connected to ground, probe cooling fan battery feed circuit. If test light illuminates, go to step 16). If test light does not illuminate, go to step 17).

13. Repair short to ground in cooling fan control circuit. After repairs, go to step 23).

14. Check terminals to cooling fan relay. Repair as necessary. After repairs, go to step 23). If terminals are okay, go to step 21).

15. Check cooling fan control circuit for open or poor connection. Repair as necessary. After repairs, go to step 23). If circuit or connection is okay, go to step 22).

16. Connect test light to battery voltage and probe cooling fan ground circuit. If test light illuminates, go to step 1. If test light does not illuminate, go to step 19).

17. Repair open or poor connection in cooling fan ignition feed circuit. After repairs, go to step 23).

18. Check for poor connections at cooling fan harness connector. Repair as necessary. After repairs, go to step 23). If connections are okay, go to step 20).

19. Repair open or poor connection in cooling fan ground circuit. After repairs, go to step 23).

20. Replace cooling fan motor. After replacing cooling and motor, go step 23).

21. Replace cooling fan relay. After replacing relay, go to step 23).

22. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.

23. Turn ignition on, with engine off. Command cooling fan on. If cooling fan operates, system is okay. If cooling fan does not operate, repeat step 1).

Posted on May 16, 2010

SOURCE: blower fan low speeds dont work just runs on high....is it the resister...check the relay seems ok

Hi Dean, I don't really know what you mean by the register, but I believe your problem is to do with the resistor which is built into the fan housing. It consists of three wire wound resistors and is fitted into the fan housing to take the benefit of the fan to cool the resistor pack. The climate fan at full speed runs directly from the battery voltage. The lower speeds run through the relevant resistors (which are of different values) and thereby run the fan at decreasing speeds. Remove the covers from the both sides of the fan housing and on one side you will see a small panel held in position be one or two screws. The panel will have cables plugged into it, which are those for the fan. To confirm you have the correct panel, turn on the ignition and the fan at full speed and disconnect the plug from the socket. the fan will stop and bingo! you have it! Remove the unit and either repair the unit or better still go to a breakers yard and buy a replacement from there before they wreck it! Fit it in, connect the plug, put back the paneling and enjoy. Regards John

Posted on Feb 18, 2012

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