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Lou P. master tech
Lou P. master tech, Mercedes Technician
Category: Mercedes
Satisfied Customers: 3736
Experience:  15 years master certified 100% fix rate and have access to factory radio codes, wiring, and instructions.
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2002 S430 fan stays on gh speed as soon as car is started,

Customer Question

2002 S430 fan stays on high speed as soon as car is started
JA: Sometimes things that you think will be really complicated end up being easy to fix with a Mercedes. The Mercedes Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so he can help you best.
Customer: coolant fans stays on high speed all the time and the ac compressor is on
JA: Are you hoping to fix this yourself?
Customer: yes
JA: Great! What have you tried so far?
Customer: change/replace coolant fan
JA: Is there anything else important you think the Mercedes Mechanic should know about your Mercedes?
Customer: also heater/ac control no working blower not coming on
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Mercedes Mechanic about your situation and then connect you two.
Submitted: 9 months ago.
Category: Mercedes
Expert:  Lou P. master tech replied 9 months ago.

Hello, there are only 2 reasons the fan will come on high,

  1. the engine control module is internally shorted
  2. the fan control module is internally shorted

the only test you can do without a scanner is to test the signal wire from the ecm to the fan to see if it has power, if the wire does have power that means the ecm is activating the fan , in that case you need to get a scanner to see if the ecm is wanting to activate the fan or not. if it is not wanting to activate the fan then the ecm is bad. if it is wanting to activate the fan then further diagnosis is required to see if the air conditioning control module is telling the ecm to activate the fan .

now if the you test for power on the signal wire and you get no voltage that means that the fan assembly is bad. the wire you need to check for power on, is on the big connector at the fan control module assembly.i will attach a picture of the location.

the yellow wire with the blue stripe is the ground signal to the fan so you want to use a meter and test from that wire to a positive source.

hope this helps. the fan module is the silver box in the picture which is under the passenger headlamp. you should be able to access it from under the bumper.

Please take a second and click the stars at the top of the screen to rate me so i may recieve my credit , 5 stars is ideal , please request me in the future. If you feel I have not been helpful please DO NOT RATE 1 or 2 stars AND WASTE YOUR MONEY , I will opt out to see if another expert can provide more or better assistance so you're not wasting your money!!. Thanks for choosing just answer. Also , if you feel i deserve one , BONUSES are GREATLY APPRECIATED ! Lou P.

Keep in mind then when you rate it does not end our conversation. you can still return here to me for follow up information if needed, Lou P.

Expert:  Lou P. master tech replied 9 months ago.

Please take a second and click the stars at the top of the screen to rate me so i may recieve my credit , 5 stars is ideal , please request me in the future. If you feel I have not been helpful please DO NOT RATE 1 or 2 stars AND WASTE YOUR MONEY , I will opt out to see if another expert can provide more or better assistance so you're not wasting your money!!. Thanks for choosing just answer. Also , if you feel i deserve one , BONUSES are GREATLY APPRECIATED ! Lou P.

Keep in mind then when you rate it does not end our conversation. you can still return here to me for follow up information if needed, Lou P.

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