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Piwoslaw 05-14-2009 03:08 AM

Radiator relay/sensor question
3 Attachment(s)
While fooling around under the hood yesterday I found a relay/sensor(?)
It's a plastic box with a metal cage on one side. Inside the cage are a spiral and a resistor(?). The module is mounted in a hole at the top left of my radiator, with the metal elements facing (almost touching) the rad. Two cables connect to the box, one with 4 wires to the top and one with 2 thicker wires to the bottom.
I didn't have time to open the box, but I did check resistance between the wire tabs:
between bottom '1' and top '4' is 1000 ohms,
between top '1' and top '2' is 150 ohms,
between top '1' and top '3', and between top '2' and top '3', are both 75 ohms.
Bottom '2' doesn't appear to be connected to anything. I believe that when hooked up, the bottom '1' connects to the '+' of the battery (the mass in my car appears to be '+', not '-').

Can anyone help me understand what this is and how it works? Is this the thermostat for my fan? BTW, my fan is supposed to be 2-speed, 1 turns on at 95*C (or 85*C with A/C on), 2 at 105*C. The fan has a 2-wire connector, but doesn't hook up directly to this module.
I'd like to know how this works, hoping I can tap into the right places for a cabin LED and grill openning motor.


vtec-e 05-14-2009 05:06 AM

That is one trick looking piece of kit there Adam! It almost certainly is for your radiator fan. How it works is beyond me however. You could try talking to someone from peugeot or citroen but i doubt they'd tell you anything. I doubt even the mechanics know how it works, only if it does or not! If it's sending an analogue signal to the ecu, as you imply, then hooking it up to an LED etc. is going to be more difficult. Well for me anyway....! But if it switches on at a given temp then you are in luck. All you need is a circuit diagram...........


vtec-e 05-14-2009 05:25 AM

I found this site after a search using the part no. in your picture. It may or may not be of use to you. Strona 189 - Katalog części - Auto-Szrot - używane auto-części pochodzenia zachodniego

Best of luck!


Piwoslaw 05-14-2009 05:53 AM


Originally Posted by vtec-e (Post 104194)
I found this site after a search using the part no. in your picture. It may or may not be of use to you. Strona 189 - Katalog części - Auto-Szrot - używane auto-części pochodzenia zachodniego

Wow, and it's in Polish:) Thanks, I'll have a look:)
I put something up on the Peugeot Klub forum, maybe someone will know.

Piwoslaw 05-18-2009 05:16 AM

I got only one partial answer from the Peugeot Klub forum, but I did find some electrical schematics for my car, and it appears that this module only regulates the speed of the fan. The coil is a thermoresistor, while the little 'resistor' just above it is supposedly a diode (though when checking resistance it was the same both ways).
The diagrams aren't exactly easy to understand, so it may take me a while to grasp everything.
If anyone want a crack at it please PM me.


vtec-e 05-18-2009 08:00 AM

So it would appear to regulate the fan speed with the use of a variable resistor. This could be used to regulate how much a grille block opens. I'm not sure how so i'll leave it to the electrical experts here.


Piwoslaw 06-05-2012 02:47 AM


I still haven't found out the workings of the speed controler from the first post:( I did find out that the fan's speed may not be 2 step, but a smooth increase between min and max speed.
Shortly after starting this thread I hooked a pair of small wires to the fan's socket, and the other end to an LED on the dash to indicate when the fan is on. The LED was always on, which means that there is always voltage in the fan's supply. I checked that when the engine is running there is 14V between the fan's leads. Apparently, not enough current to get it going, though.
So my new question is: Can I wire the LED to the fan's supply so that it is on only when the fan is spinning, ie only when there is enough current to make it spin? And can it be done so that the LED doesn't burn out when the fan goes to a higher speed? Ideal would be changing the LED's color depending on speed, but that may be too much.

drmiller100 06-05-2012 11:38 AM

wow. talk about an interesting way to run a fan.

so my guess is the magic black box measures the resistance of the coil as a function of temperature.
The hotter it gets, the more amperage it sends to the fan (like you said).

The "problem" is there is no "On" or "Off" state for the fan. The fan is variable as a function of temperature.

You COULD put an amperage gauge in series with the fan motor. Or you could put a temperature gauge next to where the relay gizmo is located - the temperature shouldn't really change that much.

Or, you could just put a temperature gauge on the engine to make sure the engine doesn't get too hot.

Piwoslaw 06-07-2012 05:54 AM

3 Attachment(s)
Today I opened the magic black box and found that there's not much magic.

It's wired up more or less like this:
  • There are two relays, let's call them R1 and R2,
  • R1 is wired to top inputs 1 and 3 (see post #1 for input numbering), and there is a ~65ohm resistor in parallel,
  • R2 is wired to top inputs 2 and 3, and there is a ~65ohm resistor in parallel,
  • Top input 4 connects to bottom input 1 (B1) through a 1000ohm resistor,
  • Closing R1 connects B1 and B2 (bottom inputs 1 & 2), resistance between B1 and B2 is ~0.1 ohm,
  • Closing R2 also connects B1 and B2, with resistance ~1 ohm.
The only magic part is that I couldn't find a connection between R2 and B1. R2 connects B2 to the diode next to the big coil in the external housing. There are four tabs in that housing, only two actually connect to the internal workings, yet all seem to be connected to each other (according to my multimeter) and to B1, but I couldn't visually see any connections.

When hooked up, B1 connects to the radiator fan's + input, B2 connects to the battery's + output.

So my guess is that when the coolant temperature exceeds 95C the ECU sends a signal (via top pin 2) to close R2 and engage the radiator fan through the big coil resistor. When coolant temp exceeds 105C the ECU closes R1 (via top pin 1) to run the fan at full speed, bypassing the resistor. Top pin 4 is probably for the ECU to check whether the relay closed and whether there is voltage in B1 going to the fan.

Question: The difference in resistance between B1 and B2 is either 0.1 or 1 ohm, depending on which relay is closed. Is 1 ohm enough to noticibly slow the fan, or maybe does the coil in increase its resistance when the radiator gets hotter (when installed, the external housing is right up against the rad)?

This gives me a new way to get a signal for a fan indicator LED in the dash: tap into the top inputs 1 or 2. I'll have to test that when I get some time.

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