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Discussion Starter · #1 ·
Hi guys,

My 04 MDX seems to be turning on the radiator fan as soon as I turn off the vehicle. I am under the impression that something other than the radiator is overheating even though the correct amount of coolant is flowing. Any ideas on what the issue may be?


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Discussion Starter · #3 ·
A stuck-closed radiator fan relay or A/F sensor relay could cause this problem. See attached wiring diagram.



good luck


Thank you so much for the feedback! I am unable to find the A/F sensor relay on rockauto or ebay. Can you please provide the part number? I would rather switch both.


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AF relay is a normally open type A relay. It is identical to many relays (Main Fuel Relays 1 and 2) on the vehicle. I don't have a part number.

Note, the PCM could be the problem if driver transistor were failed closed.

A good test of AF relay is to simply remove relay and test for power/ground. Power should be available on control power and fan feed lines (see relay cover to know which pins). Ground should NOT be available on control ground line w/ keyswitch OFF. Fan power delivery line should be open (no ground).

good luck
 

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And don't forget that the easiest way to test for a bad relay when there are several identical ones next to it is to swap 'em out... if the problem follows the relay, you've found your problem. If not, at least you've eliminated it as a possibility.
 
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