Peugeot 405 GL 1991 (carb) - Engine Cooling fans not working

Honest John Back Room » Technical matters
What is life like with your car? Let us know and win £500 in John Lewis vouchers | No thanks
View Threaded
Fri 1 Apr 2011 22:24
Peugeot 405 GL 1991 (carb) - Engine Cooling fans not working - kumah
I've been driving my 405 GL since its manufacture. It is a model fitted with air-con. 5 years ago I was forced to replace the entire engine. Since then I have had problems with the cooling fans. Due to a leakage I have also not been able to restore my aircon. Because of the shoddy work done, I had to download a Haynes Manual in order to get things right again. When the new engine was installed, it took me some time to get the engine temperature gauge to work again. I found out that there are some single pin sensors at the back of the thermostat head. One lead was connected there initially, but it wasn't showing the temperature. It took me an inordinate amount of time to find out that there are three sensors there and find the right one. Unfortunately, the cooling fans do not work when they should (from various fora and the manual I have concluded that they should work from around 88 to 90 degrees).
I realised that some wire leads had been cut irrespective of their connections to the engine. There are three plugs hanging unused in the engine area. I was also given what seems like a thermistor with the new engine. I cannot tell whether it was part of the old engine or was part of the new engine setup. I tried connecting it to any of the 3 unused plugs and even used hot water to simulate the hot radiator. It did not work. I have therefore concluded that it cannot be part of the radiator setup as I was led to believe by some info I saw online. The only info I have seen as credible is this:
You have 1 sensor for the fans & Bitron unit

1 sensor does the temp gauge & ECU (if petrol injection )

The other sensor does the "STOP" & "High temperature" warning lights

Thats why Peugeot 405s have 3 temperature sensors.

Obviously I have found the temp sensor. I attached a wire each to the remaining sensors and connected the "open" wires to the sensors whenever the engine was hot enough but there has been no response form the fans. The info I found did not say whether the sensors were single pin or double pin. But most fora spoke of double pins which is why I was initially ignoring it.
I have to add that I checked the fan relays, and they are all in proper working condition. I also read somewhere how to make the fans work fast or slow speed and tried it out using a piece of wire. It worked. All that I need now is for the fans to be triggered when the temperature gets to 88 degrees. I think because of the differences in Peugeot engines, I cannot entirely relate the diagrams in the Haynes manual to my car. For now, I have inserted a wire from under the dashboard with a switch attached to run the fan manually when the temperature approaches 80 degrees. I am an Electrical Engineer by profession, that is why I have been able to delve into the practical of the engine myself. I also cannot locate the Bitron sensor - if my car even has it.
For your information, I live in Ghana. We have a Peugeot dealer here (PRESTIGE Motors), but I live far away from them and cannot take the car there each time there is a fault. I have therefore had to rely on roadside mechs to help me out. Fortunately, the Haynes manual has provided me with much info, so I'm able to read and verify things for myself before I go to my usual mechanic. He has also seen that I know enough for him to trust my judgment - even though he does the work! Hope you can help me out with this!
Reply | Report as offensive | Link
Fri 1 Apr 2011 23:36
Peugeot 405 GL 1991 (carb) - Engine Cooling fans not working - Peter.N.

The fan arrangement is a bit complicated, it has a series - parallel arrangement depending how much cooling is needed, but I expect you have already worked that out. I f you can find the sensor that controls the fans, assuming its a switch not a thermistor, you should be able to wire it so you get some cooling when when it closes.

I have a similar arrangement on my Citroen XMs and have never been able to fathom it out - and I'm a retired TV engineer!

Reply | Report as offensive | Link
Sat 2 Apr 2011 23:02
Peugeot 405 GL 1991 (carb) - Engine Cooling fans not working - kumah
Yes, I've seen a thread somewhere that describes the Citroen fan system. It's similar. Really I just need to find the right wire, because there are only two sensors to chose from, unless it's located elsewhere at the back of the thermostat housing. That place is really hard to get at or see - even if you take the battery out.
Reply | Report as offensive | Link
Wed 4 Jul 2012 22:10
Peugeot 405 GL 1991 (carb) - Engine Cooling fans not working - dome

This is late but might help. My 405DL and S US model fans ran at normal engine operating temperature, ie all the time when warmed up. The problem was the Bitron sensor changes resistance as it gets older. I put a 100 kilohm potentiometer across the 2 contacts and kept dropping the pot resistance till the fans turned on at about 190 degrees F as they should.I think the pot resistance was about 45 K then. The Bitron 2 pin sensor is on the rear of the engine just above the exhaust manifold in the head. You have to use a mirror, get under the car, or get on top the engine with you head back against the fire wall to see it. The computer uses the bitron sensor to determine to when to turn on one fan or two. If I remember right, if you use the AC both fans might run all the time. My AC went out a couple years ago and I haven't fixed it. Hope this helps if you still need it.

Reply | Report as offensive | Link

We give you the low down on how to save on insurance, little-known tricks and tips, what insurance groups mean and how to use insurance aggregators to beat insurers.

Insurance group finder and how to save on insurance

Will you have to pay the low emissions charge?

Use our ULEZ checker to find out if your vehicle is subject to ULEZ charges. Simply enter your number plate into the Honest John ULEZ checker to see if you will have to pay to enter the London Ultra Low Emission Zone.

Check your vehicle