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87 300 D Turbo, 95 E 300 D, 96 E300 D, 98 E300TD, 00 C230 Compressor, 02 C 320 Wagon, 2010 C300
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130 Posts
Discussion Starter #1
I replaced the timing injection device on my car, so now the auxiliary fan is always on. As soon as I put the ignition on the fan starts working and never turns off. I did not touch any electrical wires that I'm aware of.
Any advice will be greatly appreciated.
 

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'95 E300 DIESEL, '91 600SEL, '92 600SEL
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17,388 Posts
Fan temp sensor has failed or engine wiring harness problem (if you still have the original engine wiring type).

Do note that this engine uses multiple engine temp sensors (gauge, fan, ECU, etc.), so be sure you get the correct type.

Also, you will most likely need to remove the intake manifold to replace this sensor so be sure to get a new intake manifold gasket (there are 2 versions based on engine #).

Lastly, make sure you remember where everything plugs into (vacuum & electrical wise) as there are a lot of connections underneath that manifold.
 

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94 E320
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209 Posts
check one thing before you do anything else

Before you do anything else make sure the wire to the sensor on the thermostat housing (it is actually a two prong connector with two wires going to it) is connected. IF this is not connected the fans will run as you described. Good Luck.
 

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87 300 D Turbo, 95 E 300 D, 96 E300 D, 98 E300TD, 00 C230 Compressor, 02 C 320 Wagon, 2010 C300
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130 Posts
Discussion Starter #4
Thank you for your advise, I checked the connector to the sensor on top of the engine and noticed that the insulation of the 2 wires were gone and they were touching each other, I separated them, put some insulation tape and the auxiliary fan doesn't turns on when cold.
Amazing!
Thank you guys for your cooperation.
 

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'90 124.128
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241 Posts
If you're not already...

Start saving up for a new engine wiring harness.

(Although,with a couple of cans of "Liquid Electrical Tape" and lots of patience
you can re-cover the Pre-Bio-Degraded insulation!)
 

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7 Posts
Thank you for your advise, I checked the connector to the sensor on top of the engine and noticed that the insulation of the 2 wires were gone and they were touching each other, I separated them, put some insulation tape and the auxiliary fan doesn't turns on when cold.
Amazing!
Thank you guys for your cooperation.
I had the same exact issue with the insulation gone and wires touching. I cut the two wires about an inch away from the plug end and slid tubular shrinkwrap on them as far as I could. Then I soldered the wires together, slid the shrinkwrap up and shrunk it with my heat gun. Then I wrapped the wires back up with that same cloth material that was on there. Now fan operates great.
 
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