Jun 25, 2010 (10 years ago)
This should give you the info required .
Wed 17 Aug 2005 15:00 Peugeot 406 cooling fans - P 2501
This is a very common problem. The two fans at the front should always run together, first at slow speeds with 6v and then if the temp stays high, they will switch to 12v and run fast.
Your non working fan has either a blown motor, or more likely, a bad relay.The other fan then compensates by always blowing on fast speed when the temp sensor actuates it.
The fans are turned on at approx 92 degrees for slow speed and 97 ish for high speed.The actual temps will be marked on the temp sensor which is screwed into the top right hand side of the rad (as viewed from the front of the car).
I had this exact problem and it turned out to be a corroded relay.On my 306 these were located in a triangular plastic box behind the front plastic grill in full view of road spray,rain,salt etc.No wonder they rusted! a bad bit of design really.
Something to get you started.
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Wed 17 Aug 2005 15:52 Peugeot 406 cooling fans - RichardW
"The fans are turned on at approx 92 degrees for slow speed and 97 ish for high speed.The actual temps will be marked on the temp sensor which is screwed into the top right hand side of the rad (as viewed from the front of the car)."
It won't be quite as simple as that on a 98 2.1TD - the fans are controlled by the Bitron unit (although this only handles the switching feeds to the relays which are still present as far as I know).
What should happen is that both fans come on slow at around 85°C, then both on high at a higher temperature (might be 100°C or so). When you switch the air con on both should come on on slow and stay on all the time the A/C is switched on. If the system detects high pressure or temperature in the A/C system then it should give high speed. Likewise of the coolant goes to the high speed temp you should get high speed.
If one fan is kaput, or there is a fault with the relays etc, then you may get only one fan on high speed when the high speed condition is reached. You should get nothing at all on low speed condition (fans are connected in series in that case).
If you are getting one fan on high speed when it should be low speed than someone's messed with the wiring.
The Bitron takes its feed from the brown sensor in the water outlet on the front of the head - if you unplug the sensor you should get both fans on full - even if the ignition is off.