Thermo fan on radiator not working

The fan is controlled by a thermo switch . It's located on the radiator and has power going to it always and when temp goes up it grounds circuit and fan come on.

check the 25 amp fuse that had fan rad on it . Check the fuses under the dash. Finally replace the fan switch in the head as it may not be communicating with the CPU to put power through the fan relay

There are several reasons why a Maxim-X fan might not run. One reason might be that the fan fuse has blown. The fan has a 10A fuse all its own which is located under the cover for the indicator lights by the ignition keyhole (there are four #2 Philips screws that need to be removed before the cover can be removed to access fuses and indicator bulbs).

If the fuse is OK, then the next possibility is that the 'Thermo Switch" which trips the fan isn't making a connection. The Thermo Switch is threaded into the thermostat housing and has a push-on wire connection. Actually, the temperature sensor is also threaded into the thermostat housing but it is the smaller of the two sensors/switches. The larger of the two, which I believe is accessible from the left side of the thermostat housing, is the switch that trips the fan. Often the push-on connection gets oxidized and needs cleaning. Often the wire connection becomes loose and can simply be tightened and pressed securely back into place to restore the connection.

Another reason the fan might not spin is that the power connector has a bad connection. From toward the right side of the fan you'll see a short length of wire (maybe a foot) with two conductors leading to what I seem to recall is a red plug. Like all the other plugs, that can oxidize and create a bad connection. The plug can also come loose if someone before you has broken the locking tab or maybe didn't plug the two halves properly together again. You'll find the plug end up around the right side of the thermostat housing.... between the thermostat housing and the right frame rail. That's also where one white and one yellow plug are tucked away (the yellow is the power plug for the left coil and the white is the power plug for the right coil). It's a pretty tight cluster of wires and plugs but finding the red one for the radiator fan power is fairly easy because tracing the wire back to the fan is fairly easy.

So, if the fuse is OK and the thermo switch is working, and the connection from the thermo switch is a good one, and the power connection for the fan is solid.... then the fan might be burnt out. If so, they come up on eBay often enough so it shouldn't be too difficult to find a replacement.

But, from my experience, my money is on the fuse first, the bad thermo switch connection second and possibly a failed thermo switch third. That's what I've seen most often. Whatever it is, it's a reasonably easy fix.

check the obvious first, water level, check the fan is switching on at temp, by removing the wires for the thermo switch,( a large brass "nut" with 2 wires attatched, on either the thermostat housing or the radiator) and connecting them together with the ignition on. If the fan kicks in then you know the fan and other electics is ok. To replace the switch, simply unscrew and replace with a new one.They are quite cheap to buy.
If the fan doesn't kick in the check the fuse, wiring for loose wires/connections/breaks. check the relay and if it has a fuse on check that also.

Here are the cooling system diagnostic steps...First does the cooling fan kick on (with engine hot)? If not, check the fuse, if good then check the thermoswitch in the radiator (it's about an inch and a half in diameter located on the lower part of the radiator with two wires ) by disconnecting the wires and touching them together (again, with engine hot...at least 190 degrees) if the fan comes on, you have a bad switch. If not connect a 10 gauge jumper wire from the battery to the fan itself (there are three terminals,,, one high, one low and ground). With power direct from the battery (and a ground wire, if necessary) fan should run... if not replace the fan assembly... if it does run then you have a bad cooling fan relay. It will be located above the fuses on the fuse block... Hope this helps...;-)

Check the fluid level in the radiator - after it cools down !

It sounds like you should replace the temperature sensor that controls the fan. This is usually located in the radiator and has electrical wires connected to it. Trace the wires from the radiator fan ( not the air conditioner fan!) to the sensor.

If the radiator is aluminum you may need special anti-freeze to prevent damage.

This really sounds like your radiator fan is working. Slow speeds under 20MPH the fan is needed badly. Over 20MPH there is enough ram air to sufficiently cool down the radiator. You should find a fuse for it in the Power Distribution Center under the hood. Check big and small. If the fuses are good and you're convinced the radiator fan isn't coming on, try swaping the rad fan relay with another in the PDC. As far as the "Check engine" lite goes, a transmission fault can turn on the lite. However if your radiator fan is not working that will also turn on the "Check engine" lite.
Good luck with that and let me know if you still have issues.

The most likely cause of this is the fan not kicking on... and the best place to start looking is the fuse for the rad fan (under the dash). If this is good check radiator thermo-switch... Observe the engine as it comes up to operating temp... if the fan does not kick on by about 200 degrees, disconnect the terminals at the switch and connect them together briefly. If the fan comes on then the switch is faulty, if not then suspect the cooling fan relay. If the fan runs normally but vehicle still overheats, the next thing to check is the T-stat. Feel the upper hose when at operating temp... it should be warm... if not remove the T-stat and reassemble... if the problem goes away it was your T-stat, if not it is either a bad pump, or a restricted (clogged) radiator. If the pump is not noisy or weeping coolant, it's probably OK... Hope this helps...;-)

there are actually 3 temp sensors. 1 is on the top of the engine that goes to temp gauge in dash has 1 wire. next to it is a 3 wire sensor for engine control and choke. on the bottom of the radiator next to the hose is a 2 wire sensor. loosen all 3 but leave connected. get engine hot past halfway point on dash gauge. with ac off disconnect 1 sensor at time. start with 2 wire under radiator. it takes the most abuse. fan will come on when you disconnect broken sensor. 2sensor must agree for fan to stay on till engine cools when turned off. note this is solution i used after verifying fuses, fuseable links and relays worked.WOO HOO! make sure you check both the fuse box under hood and fuse boxleft side of steering wheel my ECU fuse was inside my bros was outside.ECU B on my car goes to nothing and is under hood. Had it confused with ECU on wiring diagram.DOH!

P2181 is a overheating engine.  
Can be:
Bad fan themoswitch, temp sensor themostat water pump impeller fan motor or fuse on battery
check to see if fans work by turning on Air Conditioner (fans should run with A/C on). Turn A/C off, warm engine, check to see if fans come on, if they do NOT it may be thermo switch on radiator on lower left side, has 3 wire plug, takes 1-1/8" wrench/socket to remove.  This thermo switch controls fans when temp reaches 195F, if fans do not come on at engine temp 190-195F try  replace switch VW part number: 1J0-959--481-A  You can verify if the switch is bad by shorting wire 1 and 2 (fans should come on when jumpered).